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EUROCONTROL

EUROCONTROL EXPERIMENTAL CENTRE

CONTROL TOWER OPERATIONS: A LITERATURE REVIEW OF TASK ANALYSIS STUDIES

EEC Note No. 10/06

Project MMF

Issued: July 2006

The information contained in this document is the property of the EUROCONTROL Agency and no part should be reproduced in any form without the Agency’s permission.

The views expressed herein do not necessarily reflect the official views or policy of the Agency.

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Reference: EEC Note No. 10/06

Security Classification: Unclassified

Originator:

Originator (Corporate Author) Name/Location: DeepBlue s.r.l Via Basento 52/D 00198 ROMA ITALY Telephone: +39 06 85 54 801

Sponsor: Marc Bourgois Deputy Manager Innovative Research Area EUROCONTROL Experimental Centre

Sponsor (Contract Authority) Name/Location: EUROCONTROL Experimental Centre Centre de Bois des Bordes B.P.15 F – 91222 Brétigny-sur-Orge CEDEX FRANCE Telephone: +33 (0)1 69 88 75 00 WEB Site: www.eurocontrol.int

TITLE: CONTROL TOWER OPERATIONS: A LITERATURE REVIEW OF TASK ANALYSIS STUDIES

Authors Monica Tavanti (DEEPBLUE)

Date 07/2006

Pages x + 47

Figures 23

Tables 6

Annexes -

References 47

Project

MMF Task No. Sponsor

C61PT/20004 Period 2006

Distribution Statement:

(a) Controlled by: Marc Bourgois (b) Special Limitations: None

Descriptors (keywords):

Tower operations, Task analysis

Abstract:

This document constitutes an input to a larger project that aims to propose and evaluate Augmented Reality (AR) tools for Control Tower. The AR project intends to provide support to enhance the tasks carried out in the tower which, nowadays, can be limited or/and negatively influenced by poor visibility conditions (e.g. bad weather, occluded areas, etc.)

This document was essentially written for students and for readers with little knowledge of the topic. This report presents an overview of task analysis studies of the Air Traffic Controllers operating in tower, as identified by past research. In order to comply with the general aims of the AR project, this document focuses on the tasks entailing the look outside the window.

Control Tower Operations: a Literature Review of Task Analysis Studies EUROCONTROL

Project MMF – EEC Note No. 10/06 v

FOREWORD

The increasing demand for higher levels of safety and capacity require the exploration of new technologies, especially at bottlenecks in the air traffic system, such as airports.

The Augmented Reality for Tower Control project has selected a specific innovative technology (Augmented Reality), a specific ATC setting (the Control Tower), and an approach that combines the technological push with the final users’ needs and the operational constraints.

We believe that Augmented Reality (AR) could be a valuable technology to support and enhance the controller’s view-out-of-the-window. However, how can AR be applied and tailored to this specific domain?

The present note provides a literature review on task analysis studies entailing tower operations that focus on the view-out-of-the-window. The aim of this note is to identify what tasks could benefit from the introduction of AR tools.

Marc Bourgois Deputy Manager Innovative Research Area

EUROCONTROL Control Tower Operations: a Literature Review of Task Analysis Studies

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Project MMF – EEC Note No. 10/06 vii

TABLE OF CONTENTS

LIST OF FIGURES .......................................................................................................... VIII

LIST OF TABLES............................................................................................................ VIII

ACRONYMS AND GLOSSARY ........................................................................................ IX

1. PURPOSES AND STRUCTURE OF THE DOCUMENT ...............................................1

2. CONSIDERATIONS ON PAST RESEARCH ................................................................2

3. METHODOLOGICAL PREMISES ON TASK ANALYSIS ............................................3 3.1. DEFINING THE WORDS: “TASK” VS. “ACTIVITY” ....................................................... 3 3.2. TASK ANALYSIS ........................................................................................................... 3

3.2.1. Hierarchical Task Analysis ................................................................................4 3.2.2. Method for Usability Engineering.......................................................................4

3.3. COGNITIVE TASK ANALYSIS....................................................................................... 5 3.3.1. Integrated Task Analysis ...................................................................................5

3.4. ACTIVITY THEORY ....................................................................................................... 6

4. COGNITIVE MODELS ..................................................................................................8 4.1. ATC AS COGNITIVE ACTIVITY..................................................................................... 8

4.1.1. Some Concepts .................................................................................................8 4.2. STRUCTURAL COGNITIVE MODEL OF ATC............................................................... 8 4.3. THE COGNITIVE MODEL OF THE CONTROLLER’S TASK ........................................ 9

5. LITERATURE SOURCES ...........................................................................................11 5.1. CONTROLLERS’ ROLES............................................................................................. 11

6. PAST STUDIES ..........................................................................................................12 6.1. INTEGRATED TASK ANALYSIS ................................................................................. 12

6.1.1. Controller Tasks and Cognitive Processes......................................................12 6.1.2. Sub-processes.................................................................................................13 6.1.3. Control Process ...............................................................................................16 6.1.4. Tasks Process .................................................................................................16 6.1.5. Cognitive and Behavioural Profiles..................................................................18

6.2. TASK ANALYSIS FOR DESIGN .................................................................................. 20 6.2.1. MANTEA..........................................................................................................20 6.2.2. ATHOS ............................................................................................................30

6.3. INTEGRATING TASKS AND TASKS CHARACTERISATION..................................... 34 6.3.1. Task Characterisation......................................................................................35 6.3.2. “Direct Observation” Tasks..............................................................................37 6.3.3. TWR AND GND Tasks ....................................................................................37

7. GENERAL DISCUSSION............................................................................................42 7.1. OUTSIDE VIEW ........................................................................................................... 42 7.2. MENTAL PICTURE AND TRAFFIC EVOLUTION........................................................ 42 7.3. MONITORING .............................................................................................................. 42

7.3.1. Areas of interest ..............................................................................................42 7.3.2. Checking clearances .......................................................................................42


viii Project MMF - EEC Note No. 10/06

7.3.3. Operational experience ...................................................................................43 7.4. SAFETY AND CONFLICTS.......................................................................................... 43 7.5. VERBAL COMMUNICATIONS..................................................................................... 43 7.6. TRUST AND TIME ....................................................................................................... 44 7.7. VISIBILITY.................................................................................................................... 44 7.8. COLLABORATION BETWEEN CONTROLLERS ........................................................ 44

8. REFERENCES............................................................................................................45

9. ACKNOWLEDGMENTS .............................................................................................47

LIST OF FIGURES Figure 1: Structure of an activity system ....................................................................................... 6 Figure 2: Structural cognitive model of ATC (After Kallus, Barbarino & Van Damme, 1997) ........ 9 Figure 3: Cognitive model of the controller’s task (Adapted after Wickens, Mavor & McGee,

1997) ............................................................................................................................ 10 Figure 4: Basic ATC cognitive processes (After Dittmann et al., 2000)....................................... 12 Figure 5: Update mental picture/maintaining situational awareness (After Dittmann et al.,

2000) ............................................................................................................................ 13 Figure 6: Checking (After Dittmann et al., 2000) ......................................................................... 14 Figure 7: Searching for conflicts/checking safety (After Dittmann et al., 2000) ........................... 15 Figure 8: Taking over position/building up Mental Picture (After Dittmann et al., 2000).............. 17 Figure 9: Cognitive profiles (After Dittmann et al., 2000)............................................................. 19 Figure 10: Task analysis notation for the MANTEA project ........................................................... 21 Figure 11: Top-level TWR tasks (After Rossi et.al, 1996b) ........................................................... 22 Figure 12: Monitor/assess situation (After Rossi et.al, 1996b) ...................................................... 23 Figure 13: Planning aerodrome traffic (After Rossi et al., 1996b).................................................. 23 Figure 14: Plan take-offs management (After Rossi et al., 1996b)................................................ 24 Figure 15: Plan landings coordination (After Rossi et al., 1996b).................................................. 25 Figure 16: Handle new priorities (control A/C) (After Rossi et al., 1996b) ..................................... 25 Figure 17: Assist/act on A/C (After Rossi et al., 1996b) ................................................................ 26 Figure 18: Monitor/assess situation (After Rossi et al., 1996b) ..................................................... 27 Figure 19: Plan aerodrome traffic (After Rossi et al., 1996b) ........................................................ 28 Figure 20: Handle new priorities (control A/C) (After Rossi et al., 1996b) ..................................... 29 Figure 21: Guide/act on A/C (After Rossi et al., 1996b) ................................................................ 29 Figure 22: CDG tower controller task Graph 1 (After Courboulay & Kahn, 996) ........................... 31 Figure 23: CDG tower controller task graph 2 (After Courboulay & Kahn, 1996) .......................... 32

LIST OF TABLES

Table 1: CT tasks in (Adapted after Alley et al., 1988) ............................................................... 35 Table 2: Cognitive/Sensory attributes and performance requirements (Adapted after Alley

et al., 1988) .................................................................................................................. 36 Table 3: TWR tasks related to direct observation (Adapted after Alley et al., 1988) .................. 38 Table 4: TWR tasks related to criticality level, information source, cognitive/sensory attributes

and performance requirement (Adapted after Alley et al., 1988).................................. 39 Table 5: GND tasks related to direct observation (Adapted after Alley et al., 1988) .................. 40 Table 6: GND tasks related to criticality level, information source, cognitive/sensory attributes

and performance requirements (Adapted after Alley et al., 1988)................................ 41


Project MMF – EEC Note No. 10/06 ix

ACRONYMS AND GLOSSARY

Abbreviation De-Code

A/C Aircraft

AR Augmented Reality

ASMGCS Advanced Surface Movement Guidance Control System

AT Activity Theory

ATC Air Traffic Control

ATCOs Air Traffic Control Officers

ATS Air Traffic Service

CT Control Tower

CTA Cognitive Task Analysis

CTM Composite Task Model

CWP Controller Working Position

DC Distributed Cognition

FAA Federal Aviation Administration

FPS Flight Progress Strips

GND Ground Controller

GTM Generalized Task Model

HCI Human Computer Interaction

HF Human Factors

HMI Human Machine Interface

HTA Hierarchical Task Analysis

ICAO International Civil Aviation Organization

ILS Instrument Landing System

ITA Integrated Task Analysis

LTM Long-Term Memory

MAD Méthode Analytique de Description MUSE Method for Usability Engineering

NM Nautical Miles

RWY Runway SA Situation Awareness SID Standard Instrumental Departure SSR Secondary Surveillance Radar

STAR Standard Terminal Arrival Route TXY Taxiway VFR Visual Flight Rules TWR Tower Controller WM Working Memory


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Project MMF - EEC Note No. 10/06 1

1. PURPOSES AND STRUCTURE OF THE DOCUMENT

The present document constitutes an input to a larger project that aims to propose and evaluate Augmented Reality tools for Control Tower (CT). The AR project intends to provide support to enhance the tasks carried out in the tower which, nowadays, can be limited or/and negatively influenced by poor visibility conditions (e.g. bad weather, occluded areas, etc.).

The main constraint that guided the elaboration of this document was:

• Comply with the requirements of the project and thus (when possible and coherently with the results found) focusing on the tasks that entail visual observation by looking outside the tower.

This document intends to give:

• An overview of the methodologies used to describe and analyse the tasks execution by the studies found in literature.

• A brief overview of the “cognitive aspects” involved in ATC, like: cognitive principles, concepts and models that were applied to ATC and have a relation to CT activities.

• A literature reference for future investigations of CT activities.

• A review of the Task Analysis studies of the ATCOs operating in towers, as they were identified by past research.

The document is structured as following:

Section 2 General Considerations on Past Research, gives a brief outline of the limits that a generalization of the Tasks Analysis for CT activities can imply.

Section 3 Methodological Premises on Task Analysis gives a summary of the methodological approaches that were used by the studies found in literature to describe control tower tasks and activities.

Section 4 Cognitive Models provides some notions on cognitive concepts and on cognitive model of ATC.

Section 4 Literature Sources gives a brief outline of the principal studies upon which this document is based.

Section 6.1 Integrated Task Analysis, describes a study based on a method called ITA. One of the aims of the study was to assess whether the analysis of cognitive processes and tasks that was carried out for en route could be generalized to approach and aerodrome controllers.

Section 6.2 Task Analysis for Design, provides a general overview of MANTEA and ATHOS projects, which aimed to model CT tasks for design purposes.

Section 6.3 Integrating Tasks and Tasks Characterisation provides an overview of a study on TA for CT. It includes also a «task characterisation», which defines the cognitive-sensory attributes and performance requirements for some CT tasks.

Section 7 Provides a summary and a discussion of the results.


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2. CONSIDERATIONS ON PAST RESEARCH

This document aims to provide a representation of the “common and general” tasks carried out in CT, in order to have a generally valid representation of those tasks. However, two main considerations need to be made concerning this topic.

First, it is necessary to question to what extent a generally valid representation of CT tasks is realistic. It seems that the CT activities are somewhat contextual. Even if the procedures and the rules provided by the ICAO represent a standard -as: «safety is overriding requirement in aviation, standardization is one of the means to achieve it» (Kazda & Caves, 2000)- the implementation of the rules that guide the aerodrome services may be differently shaped. In other words, if the respect of the rules is usually firm, the actions taken to perform according to the rules are usually tailored to the local requirements of the aerodrome (Dittmann, Kallus & Van Damme, 2000; Choroba, 2004). The impact of regional and cultural differences in ATCOs’ job seems a recognised issue: «in Europe additional problems can arise, as there are multiple changes in language and cultural background of the controllers within very small distances». Moreover: «When attempting to harmonise ATC in Europe, one must take into account local and national working practises. […] In addition, in their communication with pilots and communication with adjacent sectors, the controllers must repeatedly deal with cultural differences» (Dittmann, et al., 2000). Things can become even more complicated if we take into account also the studies performed in the United States, where the working practices can be quite different from Europe.

Second, we have to bear in mind that the analysis of past research (eventually suggesting relevant tasks for the AR project) could be biased by some factors, such as: 1) Obsolesce; the newest study was completed in 2000 while others were concluded in late 80’: almost twenty years ago; 2) Methodological Continuity; past researches used different methods and techniques of investigation focusing on different units of analysis: in some studies some features or components are well-documented, while others are discarded, and vice versa.

To recap, there is distance between a more or less abstract model of the tasks and the real context where the operational practices are developed, thus, if the main goal is to tackle the problems and the possible breakdowns occurring in CT tasks, the specific features of a genuine working context must be taken into account, thus, the relevant issues identified by any analysis should be further studied in real working settings.



3. METHODOLOGICAL PREMISES ON TASK ANALYSIS

The overview presented in this section is an outline of the methods adopted by the specific studies found in literature (to describe CT activities) and reported in the present document. Thus, all the methods that were not used to provide a coherent and well-documented analysis of CT tasks are not included in the present section. The main goal is to give to the reader a flavour of the theoretical premises on which the literature studies were grounded. The only exception to “this rule” is represented by the section describing the Activity Theory approach, which will be used in section 7 to explain some of the limits of traditional TA methods.

3.1. DEFINING THE WORDS: “TASK” VS. “ACTIVITY”

In the previous paragraphs two expressions were given: task and activities. Sometimes these two words are confounded and improperly used. According to the definition given by Collins English Language Dictionary (1988), the term “task” means: “a piece of work which has to be done as a duty or as part of a regular routine and which may be difficult or unpleasant; [or:] an important and often difficult piece of work which is undertaken for a particular reason, especially one which is part of a larger project”; while “activity” is defined as: “a situation in which a lot of things are being done usually in order to achieve a particular purpose”. This distinction is not imposed by philological intransigence, but it suggests that “activity” is a wider concept than “task”, since: “it is structured as the processing of a series of tasks by the operator and the system” (Mancini, Marti, Palmonari & Rizzo, 2000).

These two terms differ, not only at a common sense level but, also in relation to the methodological approaches used to carry out the analysis of the users. As it is explained more in detail in the following sections, TA refers to a specific set of methods and techniques employed to describe the plans and actions executed by an operator in order to achieve a goal. By way of contrast, the term “activity” is broader than “task” and can be used either in general terms (e.g. a description of a job); or with reference to the Activity Theory, another methodological approach that is described in section 3.4.

3.2. TASK ANALYSIS

Historically tasks analysis studies were initiated by Taylor (1991) who developed standards and procedures to enhance working performances; this work inspired the development of methods to formally describe human performance, in order to increase the quantity and the quality of the work carried out (Heizer & Render, 1999).

As HCI and related fields developed, more attention was put to the understanding of what people do when they carry out some tasks. «Task analysis involves establishing who the users are, what their goals are in performing the task, what information they use in performing it, what information they generate, and what methods they employ» (Smith, Irby, Kimball, Verplank & Harslem, 1982).

TA can be deployed to make a structured description of people’s tasks and it comprises several techniques, which are targeted to capture different level of granularity and focussing on different aspects of the tasks execution.



3.2.1. Hierarchical Task Analysis

HTA (Annett & Duncan, 1967) is a method that allows examining complex tasks, breaking down each task into sub-tasks and operations in a hierarchical manner. The operation (or action) is the main unit of description of HTA. The tasks decomposition is graphically described by means of structured charts. HTA is flexible in that the “highest level” of the tasks description can be either very broad or very narrow. One of the main problems of HTA is determining when to stop the analysis. According to (Annett, Duncan, Stammers & Gray, 1971) there is a further analysis that has to be carried out, that is, performing an estimation of the costs and benefits of further proceeding with the tasks decomposition.

HTA has both pros and cons. For instance, it can be efficient, in that it allows to describe in detail a task hierarchy from a general stage to fine levels of detail; it can clearly indicate what has to be achieved in order to reach a goal; it provides the basis for further performance assessments like workload and error analysis (Callan, Siemieniuch, Sinclair, Rognin, Kirwan & Gordon, 2005).

Nevertheless, HTA is also expensive, since requires training and expertise and it can be ambiguously deployed, i.e. different notations and terminologies can be used to structure the charts; in-depth analyses of complex activities could be difficult since they require an extensive hierarchical charting. Moreover, it is a technique with a main focus on the system rather than on the user of the system (Shepherd, 2001), in fact it: «provides effective means of how the work should be organized in order to meet a system’s goals. Thus the activities of the human operator are linked directly to the requirements of the system» (Kirwan & Ainsworth, 1992). HTA discards from the analysis the context in which the operator performs.

3.2.2. Method for Usability Engineering

MUSE (Lim & Long, 1994) is a TA method that supports the development of new systems, by focusing the analysis on the systems specifications. It is structured in three phases:

1. Information elicitation and analysis; this phase consists of two level of analysis; first, the focus is put on the tasks that the users carry out with an existing system; then, the focus is shifted to a more generic model of the tasks, independent from the system in use, a Generalised Task Model (GTM).

2. Synthesis; the data collected during Phase 1 are combined to produce the HF requirements that will be mapped onto the system. The mapping is done through a Composite Task Model (CTM) that describes the tasks carried out by the user with the target system.

3. Design specification; during this last phase the actual specifications of the systems are provided, including the device-specifications and the display requirements.

MUSE has the advantage of supporting both the analysts and the designers and has a wide range of domains of application; it is sophisticated and can model the tasks of a single agent. However, MUSE has also several drawbacks. Experience and training are required to appropriately use MUSE. Moreover, it does not seem suitable for analyzing and modelling complex domains. For instance Marti (1998) argues that MUSE poses several problems for the ATC domain, specifically: the «generification» and the transition from the GTM to the CTM is not sufficiently supported by MUSE; adequate means to model the co-operation and communication among ATC actors are lacking; MUSE takes the individual as the main unit of analysis, thus discarding the implications deriving from adopting a distributed, socio-technical framework.



3.3. COGNITIVE TASK ANALYSIS

Task descriptions are usually derived by observing what people are doing. However, what is actually captured is people's explicit knowledge. Implicit knowledge (e.g. derived from the experience and/or expertise) cannot be acquired nor represented by TA.

Cognitive Task Analysis (CTA) was motivated by the remark that the execution of tasks is tightly related to the knowledge, expertise, and technological tools (Schraagen, Chipman & Shalin, 2000); «CTA covers a range of approaches used for looking at mental (hence cognitive) internal events or knowledge structures» (Kirwan & Ainsworth, 1992). Thus, differently from HTA, CTA aims to understand the cognitive processes underlying the operators’ behaviour and requires a deep understanding of the real working domain in which the operators perform.

CTA is quite demanding, in that it attempts to uncover and represent internal cognitive processes, and implicit knowledge underlying the tasks (Schraagen, Chipman & Shalin, 2000). In order to capture this knowledge, costly investigations in terms of time efforts are required. As a matter of fact, knowledge elicitation demands a very good level of understanding of the domain studied. Moreover CTA does not provide a shared set of methods to represent the knowledge domain in a systematic manner.

3.3.1. Integrated Task Analysis

ITA (Dittmann, Kallus & Van Damme, 2000) is a cognitive task analysis approach that addresses the cognitive aspects of the ATCOs’ tasks. ITA aims to «create a baseline reference for the cognitive task processes of ATCOs and to outline common aspects and differences in cognitive task processes between different services [en-route, arrival/ departure and aerodrome] and different regions within the ECAC area» (Dittmann et al., 2000). ITA is the core of big project, articulated in three phases:

1. Phase 1, creation of a set of methods compatible with the nature of the ATCOs’ job, based on: behavioural observations, post-observational and cognitive interviews, a flight-progress-strip reconstruction method and questionnaires on strain and stress.

2. Phase 2, ITA was applied (and validated) to perform analysis on en-route controllers, giving as result ten task processes related to en-route ATCOs. Because of the specific approach of ITA, the task focuses on the cognitive processes rather than on the practical execution side.

3. Phase 3, ITA techniques were applied to a sample of ECAC units, in order to validate the task processes elaborated during the previous phases; moreover, the methods were expanded and applied to the arrival/departure and aerodrome services. The task processes of the different services were then compared by means of «cognitive profiles».

The work of Dittmann et al. (2000) is quite large and attempts to create a high-level cognitive tasks structure which is then compared among different type of ATC units. The approach seems to be flexible and it allows the comparison of different working contexts. However it is also quite laborious, since several techniques of investigation need to be applied at different stages.



3.4. ACTIVITY THEORY

AT is more a theoretical approach to analyse and describe complex domains, than a method. It derives from the socio-cultural theory, founded by the Russian psychologist Vygotsky (1978), and then further developed by Leontiev (1981). Vygotsky developed a socio-cultural theory of human activity, based on Marx’s historical view of human consciousness, and on the concept of human praxis. «Activity is developed historically and collectively in specific cultural practices in which action is mediated through the use of tools and signs, and acquired individually through participation in these practices» (Daniels et al., 2005).

There is a dialectical relationship between the single human being and the society in which s/he develops and exists. This relationship is not neutral and implies a “contamination” that produces structural changes in the individual. Thus, activity is situated in a context and it is affected by the whole of it. Differently from TA, the Activity Theory acts at a higher level of abstraction and requires a holistic approach to the domain that has to be studied: its unit of analysis is not the “task”, but the “human activity”. The activity system is collective, artefact-mediated and object-oriented.

Activity is social and mediated. Any type of work is grounded in a working tradition, i.e., shared by the community of people performing the same work: this is the practice (or praxis). The individual who holds the practice can also change it (e.g., an ATCO share a practice with other controllers, but s/he can characterise it with a personal style). As labour is divided and allocated among different individuals, activities are a collective achievement, structured according to practices and “mediated”. Mediation is operated by the other actors cooperating in the same activity and by the tools (artefacts) that these actors use in order to accomplish their objectives. Artefacts are not sheer means to work, they are integrated into the social practice of work; they are invested with value as they bear the ways of performing and sharing the work.

Activity is structured. Activities are intentions in that they are «composed of goal-directed actions that must be undertaken» (Marti & Scrivani, 2002) and directed either to another individual or to an object; therefore activities are carried out through conscious actions (e.g. instructing the pilot to climb to a certain level) and they require operations, which are forms of more unconscious behaviour guided by actions and adjustable according to practical conditions. In summary, AT claims that the analysis should focus on the whole working-context and, for this reason, AT seems a well-suited approach for complex and cooperative working-settings like ATC. Engeström (1987) elaborated a model of the unit of analysis (in Figure 1), which emphasises the social elements within the activity system. According to Engeström, the outcomes of object-oriented actions are characterised by a certain degree of ambiguity and in this tension is the potential motive for change and development of the system itself. The activity develops in the interaction of the components of the unit (that should be the focus of the investigation).

Mediating artefacts

tools and signs

Subject

Figure 1: Structure of an activity system

Community Division of labour Rules

Object

Sense

Meaning Outcome



The unit of analysis is quite broad, and thus it is complicated to tackle it. It is suggested to always «look for troubles» (Engeström, 2004), e.g. tensions or conflicts between or within the elements of the activity system, in order to discover problems and potential breakdowns. AT uses a range of techniques to collect the data (video recording and analysis, interviews, observations, content analysis of the communications, debriefing sessions, focus groups, etc.) these techniques can be expensive, in terms of time and organisation. Moreover, widely-shared methods to represent the results do not seem available so far.

There are other approaches similar to the Vygotsky’s idea of activity as a socio-cultural mediated system and to the idea that social groups have «mind-like properties» (Minsky, 1985), for example, the Distributed Cognition (DC) approach (Hutchins, 2000). DC «takes its unit of analysis a culturally constituted functional group rather than an individual mind» (Hutchins & Klausen, 2000). Unlike the traditional cognitive science, that represents cognitive processes of single agents, when observing human activity «in the wild», the cognitive process is distributed across all the elements constituting the context (society, artefacts and the interaction with them), in a continous coordination between internal and external structures.



4. COGNITIVE MODELS

4.1. ATC AS COGNITIVE ACTIVITY

This section introduces some notions related to cognition; especially, the processes and the concepts that are often used in ATC-related research. Moreover, two cognitive models of the ATC tasks are herein described. These models share the basic principle upon which they are grounded: an information processing system, where the human being processes external inputs and responds back to such stimuli. ATC is often defined as an «information processing activity, which is governed by rules, plans and acquired knowledge» (Kallus, Barbarino & Van Damme, 1997); more specifically, the basics of the ATC activity are dependent on the search, the selection, the integration, the communication of information, and on feedback responses (Kallus et al., 1997). Also Wickens et al. (1997) point out that there are relationships between the tasks performed and the information-processing mechanisms employed by the controllers.

4.1.1. Some Concepts

Before continuing with the description of the models, some concepts need to be briefly introduced. First, a distinction between mental model and mental picture has to be made. While mental models refer to our understanding of a system and its parts (e.g. how it works, etc.) «the mental picture of a situation represents the mental model and the information provided by the environment» (Kallus et al., 1997).

These two concepts relate to the notion of situational awareness (SA), which is «the perception of the elements in the environment within a volume of time and space, the comprehension of their meaning, and the projection of their status in the near future» (Endsley, 1990). «Situational awareness is given as long as the mental picture and the information about the situational conditions from the environment correspond adequately» (Kallus et al., 1997). Maintaning SA is necessary to planning, taking the right decision at the right moment and being able to predict future statuses.

4.2. STRUCTURAL COGNITIVE MODEL OF ATC

The first cognitive model herein presented was elaborated by Kallus, Barbarino & Van Damme (1997). The model is structured into four main components (cf. Figure 2): the long-term memory structure (or LTM, in which the ATC mental model is stored); the working memory (or, WM, characterised by limited capacity; losing the traffic picture may be attributed to the working memory limited capacity/ proneness to interferences); the Input/Output unit (I/O, that governs the selection of information responses); the process control system (or PCS, that organises the interaction among WM, LTM and I/O system) whose main tasks are (Kallus, 1996):

• Controlling the back-up rate of the mental picture; • Attentional focus (selection of zooming-parameters); • Setting of interruption-thresholds (thresholds to switch from one task to a different one or

to attend to environmental stimuli); • Allocation of controllers’ activation and attentional resources; • Controlling the sequencing of actions; • Checking the correct execution of short-term plans; • Organizing intentional forgetting and termination of tasks.



Figure 2: Structural cognitive model of ATC (After Kallus, Barbarino & Van Damme, 1997)

4.3. THE COGNITIVE MODEL OF THE CONTROLLER’S TASK

Wickens (1992) proposes a model (in Fig. 3) that highlights the relation between the tasks and the cognitive processing mechanisms used by the controllers.

The model includes five cognitive stages occurring «between the events [on the left of the model shown in Figure 3] and the actions [on its right]: selective attention perception, situation awareness, planning and decision-making, and action execution» (Wickens, Mavor & McGee, 1997). The basic idea of the model is that controllers perceive the events in order to maintain SA, which is the main input to decision-making processes. The model takes into account also memory, divided in immediate memory (guiding and maintaining the awareness of the current situation), prospective memory (keeping track of the actions that have to be performed in the future) and long-term memory (from which the knowledge necessary to carry out the tasks is taken).



Figure 3: Cognitive model of the controller’s task (Adapted after Wickens, Mavor & McGee, 1997)

Sel

ectiv

e at

tent

ion

Per

cept

ion

Situation Awareness

Phonetic working memory Predictions Mental model Spatial working memory

Decision making and planning

Vocal Intentions and plans

Manual

Act

ion

exec

utio

n

Airspace, aircraft, Organization, individual equipment

Strategies for allocating attention, remembering, verifying and improving situation awareness, verifying and improving planning

Long-term memory

ProceduresTasksGoals

Constraints

Communications

Keyboard

External events Aircraft Weather

Radio Weather reports

Displays Strips

Perceived events

Attentional resources

Tools

Immediate memory Prospective memory



5. LITERATURE SOURCES

The information sources used for this manuscript consist of relevant reports and papers that can be considered decisive, since they address the issue of task-analysis for CT in a structured and comprehensive manner. They are:

• Section 6.1. This section gives the main results of the study carried out by (Dittmann, Kallus & Van Damme (2000). This report describes a method and a structured description of ATCOs tasks focusing on the cognitive process that are implied in the activity.

• Section 6.2. This section provides the results of three studies. The first one (Rossi, Gonnord, Paul, Darche, Mariano, Paggio, Ferreira, Adami, D’Aloia, Hessellink, Moyaux & Naves, 1996b), provides a GTM for the TWR and the GND positions. The study is complemented by the results of Marti (1988), in which a more detailed description of the tasks and of the method used to produce the GTM are given. The third study (Courboulay & Kahn, 1996) concerns the task analysis of tower controller of the Paris-Charles-De Gaulle tower.

• Section 6.3. This section provides some results of the study carried out by Alley, Ammerman, Fairhurst, Hostetler & Jones (1988). This large report is the Volume V of a group of seven documents that describe ATCOs’ operational tasks. Volume V is dedicated to Tower, Ground and Clearance Delivery positions. This study is a milestone in the field and it provides the readers with an amount of very interesting information.

5.1. CONTROLLERS’ ROLES

All the investigations herein reported focus on two CT positions, TWR and GND. The investigation carried out by (Alley, Ammerman, Fairhurst, Hostetler & Jones, 1988) provides an examination of the Clearance Delivery/Flight Data roles; yet, the present document will not address these roles, leaving more space to TWR and GND. As a matter of fact, the GND and the TWR are the actual controlling positions (Wenneberg, 2005), hence the Clearance Delivery/Flight Data roles in CT may be of little relevance for the AR project.



6. PAST STUDIES

6.1. INTEGRATED TASK ANALYSIS

The following section presents an analysis that focuses on the cognitive aspects of the tower activities and looks at the tasks emphasising memory and decision-making processes.

6.1.1. Controller Tasks and Cognitive Processes

As mentioned in section 3.3.1, during the Phase 2 of the project carried out by Dittmann et al. (2000), ten different basic processes concerning the en-route controllers were identified.

Namely, there are three main process levels, articulated into four sub-processes, five task processes and one control process, as described in Figure 4.

4 Sub-processes → Updating mental picture / maintaining situational awareness → Checking

→ Searching conflicts

→ Issuing instructions

1 Control Process → Switching attention

5 Task Processes → Taking over position / building up mental picture → Monitoring

→ Managing routine traffic

→ Managing requests / Assisting pilots

→ Solving conflicts

Figure 4: Basic ATC cognitive processes (After Dittmann et al., 2000)

During the Phase 3, ITA was applied to an ECAC sample of fifteen units. The Phase 3 had several objectives: 1) validate the task processes of en-route control; 2) expand the application of the methods to aerodrome and arrival/departure control; 3) develop and define a method (the cognitive profiles) to compare units and services according to the different cognitive processes. In the study, 82 ATCOs were involved; among them twenty-five were aerodrome controllers (17 TWR and 8 GND) of four regions (North, Central, South-East and South-West Europe

The task processes were illustrated with flowcharts that provide graphical indications about the psychological functions entailed in the cognitive processes. For instance, light-grey fill-colours indicate a separation of the memory processes, dark-grey specify evaluative/decision processes, while white boxes characterise observable behaviour. Dashed lines/boxes indicate optional actions and incomplete dashed boxes designate comments. The authors acknowledge that the extent of this structured representation of the tasks is limited by some factors, either in the form (e.g. the terms used to describe some tasks might not correspond completely to the ATC terms, etc.) or in the substance (they refer to normal traffic situations and discard emergencies, they discard task-sharing processes, etc.).



The following sections briefly describe the core points of every process, with special attention to the aerodrome services. Some flow charts -providing specific information for the aerodrome controller and/or tackling the view out the window- are reported; the elements relevant for the purposes of the AR project are encircled in red. The complete review of the charts can be found in (Dittmann et al., 2000).

6.1.2. Sub-processes

6.1.2.1. Updating Mental Picture/Maintaining Situational Awareness

The controllers make anticipations about the possible future states of the traffic in order to maintain an adequate mental picture of the traffic. The anticipations made by the aerodrome controllers, are usually very quick and functional to the maintenance of a short-term plan. If there are discrepancies between the actual situation of the traffic and the mental pictures, then the controllers have to make a sort of «diagnosis», that is, trying to explain the inconsistencies. In order to «make diagnoses», the controllers need to access the sources providing information about the traffic. As reported in Figure 5, looking outside is an important source of information for aerodrome controllers. When a “good fit” between the traffic conditions and the mental picture is achieved, the mental picture is updated.

Figure 5: Update mental picture/maintaining situational awareness (After Dittmann et al., 2000)



6.1.2.2. Checking

Checking entails a sequence of tasks that support the verification of some information (e.g. Flight Progress Strips, etc.); this process can be triggered by some external events (e.g. a reminder that was set, unexpected information was received, etc.). The outcomes of this process consist of a confirmation/update of the ATCOs’ mental picture. The authors of the study suggest that aerodrome controllers may be engaged quite frequently in a checking process, because the mental picture updates are more likely to be frequent and short (cf. Figure 6).

This process engage the aerodrome controllers in scanning tasks directed to the areodrome, by looking outside the window of the tower.

Figure 6: Checking (After Dittmann et al., 2000)



6.1.2.3. Searching for Conflicts/checking Safety

This task is central for all controllers, independently from the control area in which they work. In order to assess potential conflicts, information must be extracted from different sources; the process is guided by the controllers’ mental model and includes a «selection of the relevant data». The controllers have a sort of «conflicts library» formed on their experience; they know the «most critical parts, where possible conflicts are more likely to occur». Aerodrome controllers are likely to use this «library of possible events» and take into account a number of parameters, when the possibility of potential conflicts has to be evaluated (like the A/C performance, type and speed, and the trust toward pilots). Trust in pilots seems to play a role in the ATCOs’ decisions (cf. Figure 7). For example, Dittmann et al. mention that the decision about letting an A/C taking off between two landings, is often guided by trust in pilots: if the ATCO is sure that the pilot is very reactive and will take off immediately after the clearance, then the A/C will be cleared to take off. The main source of information for detecting potential conflicts is the view outside.

Figure 7: Searching for conflicts/checking safety (After Dittmann et al., 2000)



6.1.2.4. Issuing Instructions

Dittmann et al. state that issuing instructions is a quite habitual action and that timing is an important factor for this sub-process, which is governed by the mental picture, short-term sector plans and a «highly automated cognitive script of the actions». Monitoring the read-back plays a key role in this process. If the instructions are not adequately executed, the controller has to evaluate the impact of the deviation on safety and to re-issue the instruction if necessary. The authors suspect that in the aerodrome area, the issuing of instructions can be done with higher frequency for some periods of time, depending on the amount of traffic managed.

6.1.3. Control Process

6.1.3.1. Switching Attention

This process refers to the tasks that need to be carried out in parallel, and therefore, to the fact that attention must be allocated and switched to several tasks. Since there is a general tendency to avoid many tasks waiting for action, the controllers are likely to follow a sort of planned ordering according to which the tasks are executed. If the analysis of the situation requires the execution of a high-priority task, the ATCOs set a sort of «time-window integrated into the current plan». A reminder can also be set, in order to ensure that the “dropped task” (which is unfinished, because a higher-priority task was identified) will be completed. The high-priority task is then executed.

Then, a checking sub-process is performed and the action hierarchy is reviewed. If the higher priority task is not finished at the end of the time window, the controller may set a new reminder, update her/his action hierarchy and perform another checking. If a new higher priority task is identified, a new time-window may be opened and the task accomplished, etc.

The main problem implied in this process is that, if too many tasks are left pending, memory could be overloaded and controllers may forget to go back to unfinished tasks.

6.1.4. Tasks Process

6.1.4.1. Taking over Position/Building up Mental Picture

Usually, to start, the controller taking over the shift is debriefed by the “previous” ATCO. Then, the controller first tries to get a general impression of the traffic, by looking outside («aircraft taxiing, aircraft in holding or waiting for departure on the runway»), at the radar, at the weather displays, and at the FPSs.

The mental picture is elaborated starting from the mental model, which is then updated and integrated with the current traffic situation. If the possibility of potential safety problems is recognised, the controller does not take over the position. Usually, safety problems have to be solved by the “previous controller”: the time-windows are very short in CT, and every potential criticality has to be solved immediately (cf. Figure 8).



Figure 8: Taking over position/building up Mental Picture (After Dittmann et al., 2000)

6.1.4.2. Monitoring

This task starts with a mental picture update and conflicts search. Monitoring could be roughly called “watching and waiting”. In other words, no particular action has to be taken by the controller, unless new information inputs cause a response. When necessary, the controllers can take take actions in order to: solve conflicts, managing pilots’ requests, managing routine traffic; otherwise they monitor the situation, maintaining vigilance and being ready to respond if action is required.

6.1.4.3. Managing Routine Traffic

This task process entails several cognitive sub-processes (checking, searching conflicts, updating the mental picture, and issuing instructions). This process is characterised by particular parameters for the aerodrome control. The speed characterising the changes of conditions and, consequently, the speed requested to make decisions and take the adequate actions, is quite fast. Especially with dense traffic, ATCOs have to work very quickly. According to the authors: «As regards the safety-efficiency dimension of decision-making criteria, the balance will move more in favour of efficiency and aerodrome controllers may make more risky decisions in order to keep the traffic flowing». When the traffic is very dense, if the aerodrome has one RWY or even crossed RWYs for arrivals and departures: «the time windows for putting a departure between two arrivals are much tighter, and aerodrome controllers have to make very precise estimations and to reach instant decisions».



In such cases, experience can be very useful. Moreover, the aerodrome controllers cannot pre-plan as much as the en-route controllers do, because the times are much shorter: 15 minutes against 5 minutes, at most.

6.1.4.4. Managing requests/Assisting pilots

ATCOs evaluate pilots’ requests according to workload, safety, and time criteria. For instance, if a direct route is requested by the pilot, the controller evaluates the possible impacts of the request. If safety seems at risk, then the controller can evaluate the time required to work out a different strategy, or if the workload is very high, the request can be denied. The parameters of this process are different for the aerodrome control. Being the time so tight, the aerodrome controllers are less likely to negotiate the requests with the pilots or with colleagues; the final decisions are instantaneous and the time for choosing alternatives is very little, if not missing at all.

6.1.4.5. Solving Conflicts

ATCOs can either decide to solve a pending conflict immediately, or monitor it, while performing other tasks (and therefore switching attention). The resolution of the conflict usually requires the controllers to retrieve a solution in a sort of «conflict resolution library». Usually the controllers use routine solutions, even if a less common solution could be more adequate to the current situation. Resolving a conflict implies the issuing of the right instructions to the pilots and, in some cases, the coordination with colleagues. When the conflict is solved, controllers update their mental picture and proceed with the execution of other tasks. If the conflict is not solved, then the controller has to use a back-up plan which is usually safe, but not always very efficient. If time is available, the conflict resolution library could be reviewed and a more efficient plan could be found. For the aerodrome controllers, the parameters that govern this task process are somewhat different. Since time is very rigid, the conflict resolutions always have the highest priority. In addition, if the first solution does not work adequately, a back-up plan has to be immediately implemented: usually, there is never enough time to find both safe and efficient solutions.

6.1.5. Cognitive and Behavioural Profiles

The study of presents additional results in the form of cognitive and behavioural profiles of the controllers. In the following sections a short overview of the profiles is given.

6.1.5.1. Cognitive Profiles

In order to define a common basis to compare the profiles of en-route, arrival/departure and aerodrome controllers, the authors carried out some interviews. Then, they selected a concept that defines the type of information processing, and used it as the main parameter of the analysis; this concept is top-down versus bottom-up processing. Top-down process refers to «activities that are governed by plans, mental models, intentions and rules. Top-down behaviour can be characterised as being proactive». Bottom-up processes are: «controlled by external cues and commands. […] primarily driven by incoming information. […] Bottom-up behaviour can be characterised as being reactive or data-driven. The automation process turns simple activities into situational-driven, bottom-up behaviour» (op.cit.).



The ten processes described in section 6.1, were rated and their position within a scale (ranging from 1=definitely bottom-up to 5=definitely top-down) was set1.

Figure 9: Cognitive profiles (After Dittmann et al., 2000)

In Figure 9 a graphical description of the information processing type (for the three control services) is given. The aerodrome controllers seem to follow bottom-up approaches for almost all the tasks identified2. The interesting result is that the aerodrome controllers act in a very reactive manner. For instance, potential conflicts cannot be detected fairly in advance as it is for en-route, but rather on a very short-term basis. Pre-planning the tasks in a long-term manner is almost impossible; time is so short that actions are taken as immediate replies to the events.

6.1.5.2. Behavioural Profiles

The behavioural profiles were derived from observations data. The data was collected and structured according to three different observations grids: task units (e.g. accepting A/C, clearances issued, etc.); call survey (the types of communications); information flow sheet (the partners, the frequency and the direction of the communications). One of the constraints of the study was to perform observations during high traffic loads (rated subjectively by the ATCOs). However, for operational reasons this was not feasible everywhere.

1

The procedure and the methods for the ratings are more complex than it is described here. However, going into the methodological details of the study, is beyond the scope of this document.

2 The numbers in the diagram represent the ratings of the scale where 1 corresponds to definitely bottom-up and 5 to definitely top-down; thus bottom-up ratings are closer to the centre of the diagram.



The results indicate that the CT positions have fairly high communications with pilots for routine tasks. The authors, however, do not fully ascribe this fact to the amount of traffic load (presumably high during the observation phase); rather they see this factor as a function of the controllers’ working style: coherently with their cognitive profile, the aerodrome controllers seem to follow a bottom-up processing of the information, which is triggered by external cues and events. In addition, the call survey indicates that the number of contacts per each A/C is quite high in tower.

6.2. TASK ANALYSIS FOR DESIGN

The following sections provide two examples of HTA applied to tower tasks: the MANTEA and ATHOS projects. The first example presents two general task models for the TWR and GND positions, while the second concerns the TWR position of a French tower. Both studies were performed with the aim of designing new system tools.

As stated in the section 3.2.1, HTA is an efficient method, but it can be very expensive. For instance, the analysis for the MANTEA and ATHOS projects seem to cover a wide space and focus on a fine level of detail: practical tasks (e.g. updating the strips) were included in the analysis.

In order to provide a more manageable account of the studies, the task graphs are here complemented with a textual description that clarifies some definitions and terms. Red circles are used to highlight the tasks that seem linked to the outside view.

6.2.1. MANTEA

The project MANTEA-TR1036 ended in 2000 (Paul, Zografos, Hesselink, 2000). It aimed to provide automated support to tower controllers with decision-making tools, coordinated with terminal and en-route operations. The MANTEA tools entailed automated functions like surface traffic planning and monitoring of conformance with instructions, detection of potential conflicts and their resolution (Rossi et al., 1996a).

The target CWPs of MANTEA were the TWR and GND. The task analysis of these positions was carried out in two towers, Rome-Fiumicino and Amsterdam-Schipol (Rossi et al., 1996b). The method used to perform the TA follows the typical decomposition of main tasks into sub-tasks, as in a traditional HTA.

The task notation was taken from TKS (Johnson & Johnson, 1991), and the additional task description (in the form of tables providing information not contained in the task graphs) was taken from MAD (Scapin & Pierret-Golbreich, 1989). The notation of the graphs is rather complex, however the main symbols can be summarised as following.



The task A has prerequisite task H. A is a task composed of two sub-tasks, B and C. The arc linking the boxes containing B and C, means that both the two sub-tasks have to be performed (AND). The arrow connecting the boxes B and Aindicates that the performance of task A should end with the sub-task B. The arr ow between the boxes Band C means that the sub-task B has to be carried out before C. The double arrow means that the task B and C are interleaved. The “+” sign means that the C task is executed in a loop. The double box around B means that B can be further decomposed and it will be described separately. The curved arrow connecting the boxes D and E, means that there is a strict precedence and that D must be performed before E.

A

B

C

+

D

E

H

PreReq

Figure 10: Task analysis notation for the MANTEA project

Starting from the task models of the Italian and Dutch towers, two unified task models were elaborated: one for the TWR and one for the GND position. Since the aim of MANTEA was the design of support tools, the unified models aimed to be a generally valid and representative description of the ATCOs’ tasks, independent from the systems used in the specific working contexts. MUSE was used to produce a Generalised Task Model (cf. section 3.2.2).

The available MANTEA documentation reports in detail the Generalised Task Models for TWR and GND. However, as the authors state, there are some distinctions that have to be made. First, there is a difference between the task models for Fiumicino and Schipol. As a matter of fact, the level of detail and the style of the task models are different. This may be attributed to the difference in the application of the method but also to the regional differences in the way the controllers work.

Second, there is a difference between the actual tasks observed in the two locations and the GTM. However, the GTM was evaluated: «on the basis of the compliance of the model with the current activities in the different airports, taking into account completeness, accuracy, expressiveness of the model, representativity of the activities, resulting scope of the model» (Marti, 1998). Moreover the controllers involved in the project contributed in the construction of the GTM, ensuring a certain degree of validity for the tasks identified.



6.2.1.1. TWR Tasks

At the top-level of the tasks hierarchy, the main task “guide/control landings and take-offs” was identified. This task was broken down into six sub-tasks: 1) Monitor/assess situation; 2) Planning aerodrome traffic; 3) Handle new priorities (control A/C); 4) Guidance (act and assist on A/C); 5) Configure RWY usage; 6) Communicate/Coordinate with other controllers.

guide/controllandings

andtake-offs

monitor/assesssituation

assist/act on a/c

plantraffic

management

communicate/coordinatewith othercontrollers

configurerunwayusage

handlenew

priorities(control a/c)

Figure 11: Top-level TWR tasks (After Rossi et.al, 1996b)

1. Monitor/assess situation

Monitoring is mainly based on visual inspection (Marti, 1998) and it is used to form a mental picture of the traffic situation. Monitoring the RWY is a critical function for the TWR. This task was further divided into a series of sub-tasks describing the collection of information needed to perform monitoring tasks (for instance, in order to monitor the RWY the TWR scans the available instruments and looks outside). Consistently with the results presented in section 6.1, the forecast of the traffic evolution and the planning entails very short times.

Gather/recall context information (constraints of the day, meteorological conditions). This task summarises the activity through which the data necessary for the situation assessment is carried out.

Monitor RWYs is performed through 3 sub-tasks (depending on the specific environment there could be different instruments and tools that the convey the information used by the controllers): looking outside, looking at the radar, looking at other instruments.

Assess current traffic/forecast traffic evolution (up to 5 minutes).

Update mental picture of situation for planning/guidance purposes. This task was equally identified in the two towers. The traffic situation is kept in the form of a mental picture. Sequencing and timing information is stored in the flightstrips.




updatementalpicture

of situation for planning/guidance

purposes

monitorrunways

lookoutisde

lookat radar

look atother

instrumentswatch

separation

watchplan

deviations

watchrunway

incursions

assesscurrent

traffic/forecasttraffic

evolution(up to 5 minutes)

gather/recallcontext

information(constraints of the day,

met conditions)

Figure 12: Monitor/assess situation (After Rossi et.al, 1996b)

plantraffic

management

planlandings

coordination

authoriseVFR

overflying

plantakeoffs

management

Figure 13: Planning aerodrome traffic (After Rossi et al., 1996b)

2. Planning aerodrome traffic

Tower controllers’ main tasks involve the monitoring of the RWY and the management of landing and departing traffic.

In the description of this task the term “planning” was used. Given the fact that forecasts of the traffic are made on a short-term basis (cf. previous task description), probably this term does not refer to related to long-term working ahead schemes. This task involves all the aerodrome movements (arrivals, departures, VFR flights). A relevant source of information is constituted by the strips, which are arranged in a strip-board, according to temporal order rules. If there are gaps in the sequence, new traffic can be inserted (Marti, 1998). This task was broken down into three main sub-tasks: plan takeoffs management, plan landings coordination and authorise VFR over-flying (cf. Figure 13).



These three sub-asks were additionally broken down into a hierarchy of sub-tasks.

Plan takeoffs management; this task entails the management of takeoffs and includes a short-term plan of the departing traffic organisation, the assessment of the acceptance rate (i.e., the rate of takeoffs which has to be in line with constraints such as meteo conditions and intersections with inbound traffic), the weighting of constraints related to the traffic (i.e. the slots) and the set up of the departing sequence.

The assessment of the current traffic/forecast traffic evolution is done up to 5 minutes. A part of the take offs management task involves the decision concerning the acceptance rate (expressed as time separation in minutes). The task decide on which A/C to act first refers to the situation in which there is a list of pending departures. The controller has to select an A/C, and, if necessary, adjust the departure sequence so that A/C constraints are matched.

plantakeoffs

management

determineacceptance

rate

assesscurrent

traffic/forecatstraffic

evolution(up to 5 minutes)

lookoutside

lookat radar

checkintersectionswith inbound

traffic

check metconditions

establishtrafficplan

checkslots

checkouboundsequence

adjustdeparturesequence

decide onwhich a/cto act first

checkdeparturesequence

on flightstrips

Figure 14: Plan take-offs management (After Rossi et al., 1996b)

Plan landings coordination; this task refers to the management of landing traffic. The coordination is usually performed with the approach sector that manages the arrivals until their final landing phase. Meteorological conditions and intersections with outbound traffic are important constraints to determine the rate of acceptance of arriving traffic.

Another cluster of tasks entails the authorisation to VFR over-flying. This task is composed of three sub-tasks: checking the RWY in use, check the actual traffic, and coordinate the overflying with the Approach unit. Rossi et al. (1996b) state that this task was identified only in Fiumicino, where VFR over-flying traffic is observed few times per day, but not in Schipol.



planlandings

coordination

checkinboundsequence

on flightstrips

determineacceptance

rate

checkintersections

with outboundtraffic

check metconditions

Figure 15: Plan landings coordination (After Rossi et al., 1996b)

3. Handle new priorities (control A/C)

This task was broken down into two main sub-tasks. The tasks involve the detection and the solving of conflicts and plan deviations. The controllers have to assess whether the actual traffic situation is safe; when necessary instructions are issued to pilots. This task requires the ATCOs to anticipate few minutes ahead the traffic situation (Marti, 1998). It has similarities with the tasks identified by Dittmann et al. (2000) since the detection of deviations or conflicts interrupt the current tasks and receive the highest priority.

handlenew


handleplan

deviations

solveseparationconflicts

Figure 16: Handle new priorities (control A/C) (After Rossi et al., 1996b)



assist/act on a/c

configurerunwaylights

assist/act oninbound

a/c

assist/act onoutbound

a/c

supplyinformation

to a/c(met, positionin sequence)

monitortake-off

update/deliver

flightstrip

guidefinal

approach

monitorapproach

handlemissed

approach

checkand issuelanding

clearance

update/deliver

flightstrip

supply infoto a/c

(met, sequencenumber for

landing,traffic ahead

of a/c)

checkand issuetake-off

clearance

Figure 17: Assist/act on A/C (After Rossi et al., 1996b)

4. Guidance (Assist/act on A/C)

Some these tasks refer to routine activities of the tower controllers, with respect to arriving and departing traffic (issuing clearances and information, monitoring takeoffs and landings, etc.). Other tasks concern more “practical matters” (update and delivery of the paper strip) and less common events (handling a missed approach).

5. Configure RWY usage

The best configuration for the RWY use is decided according to the meteorological conditions, the RWY operation status and the TXY configuration (Marti, 1998).

6. Communicate/Coordinate with other controllers

The communications and coordination are mainly done with the GND, the supervisor and the approach controller (Marti, 1998)3.

3 This issue is important and will be discussedin section 7.



6.2.1.2. GND Tasks

At the top-level of the tasks hierarchy the main task “guide/control A/C movements on ground” was identified. This macro-task was broken down into five main tasks: 1) Monitor/assess situation; 2) Planning aerodrome traffic; 3) Handle new priorities (control A/C); 4) Guidance (act and assist on A/C); 5) Communicate/Coordinate with other controllers.

watchseparation

watchplan

deviations

updatemental

picture ofsituation for

planning/guidancepurposes

lookoutside

monitorsituation

assessactual

traffic/forecasttraffic

evolution (up to 5 minutes)

look atflightstrips


look atmonitoringinstruments

gather/recallcontext

information(aerodrome

configuration,constraints of the day,

met conditions)

Figure 18: Monitor/assess situation (After Rossi et al., 1996b)

1. Monitor/assess situation

The monitor/assess situation task was further broken down into four sub-tasks.

Gather/recall context information (constraints of the day, meteorological conditions). This task summarises the activity through which the data necessary for the situation assessment is carried out.

Monitor situation is performed through 3 sub-tasks (depending on the tower there could be different instruments and tools that the convey the information used by the controllers).

Assess current traffic/forecast traffic evolution (up to 5 minutes) implies watching separation and plan deviations.

Update mental picture of situation for planning/guidance purposes. This task was equally identified in the two towers. The traffic situation is kept in the form of a mental picture. Also planning decisions are kept in mind, except for sequencing and timing information (stored in the flight-strips).



2. Plan aerodrome traffic

This task mainly involves the preparation of the departures sequence trying to match A/C constraints and fill the gaps in the sequence.

Tactical planning (plan ahead) refers to the planning based on the Estimated Off Block Time, and entails the establishing of a sort of priority list according to the scheduled departures time. As stated by the authors, this task may be present -or not- according to the specific characteristics of the aerodrome. For example, in Fiumicino this is not a current practice for the GND, due to the high degree of uncertainty; even if in some occasions a sort of pre-planning is performed by a departures coordinator, when assigning a start-up time to the A/C that made the request.

Building departure sequence entails the organisation of the traffic sequence according to some criteria, namely, the slots and the exit SID. It is common practice to build efficient sequences, so that, whenever a gap is discovered in the order, it is filled. Such a pre-organised structure for the sequence is not always planned ahead.

planaerodrome

traffic

builddeparturesequence

tacticalplanning

(plan ahead)

assess situation(form "ad hoc"

picture)

find bestposition in sequence

(identify gaps for a/c)

collectinformation

on a/c(slot and other

constraints,exit SID)

assesscurrent/anticipated

situation

builda taxi-plan(establish

traffic plan)

Figure 19: Plan aerodrome traffic (After Rossi et al., 1996b)



3. Handle new priorities (control A/C)

The tasks involve the detection and the solving of conflicts and plan deviations. It has the same structure as the one used for TWR position and refers to separation assessment, possible incursions, and intersections. It should be noted, however, that the GND principal area of interest are the TXYs.

handlenew


handleplan

deviations

solveseparationconflicts

Figure 20: Handle new priorities (control A/C) (After Rossi et al., 1996b)

assist/act on outbound

a/cassist/act on

inbounda/c

locate/assume

a/c

check andissue

pushbackclearance

checkand issue

taxiclearance

givetaxiing

instructions

update/deliver

flightstrips

communicateroute orassignedparking

update/deliver

flightstrips

assist/act on a/c

supplyinformation

to a/c

Figure 21: Guide/act on A/C (After Rossi et al., 1996b)

4. Guide act on A/C

This task was broken down into two main sub-tasks, which, in turn, were divided into the tasks entailing outbound and inbound traffic. The outbound traffic requires more tasks to be carried out.



6.2.2. ATHOS

The project ATHOS (Airport Tower Harmonised cOntroller System-TR1005) started in 1996 and ended in 2000. The project aimed to elaborate a new HMI for airport tower CWP, to be integrated in future A-SMGCS. The ATHOS project also provided a HMI mock-up that integrated different tools and technologies (as the ones used in the different regional CT) into the new A-SMGCS functions. For the scope of this document, the most interesting part of the ATHOS project, concerns the elicitation of the users’ requirements.

The data about users was collected at five representative airports: Paris-Charles-De Gaulle, Madrid-Barajas, Palma de Mallorca, Amsterdam-Schipol and Frankfurt (Pham-Dumesnil, 2000). After an on-site study for every CT, a generic task analysis model (for TWR and GND) was produced in order to provide a reliable base for the specifications of the new HMI. The available documentation about ATHOS, with specific reference to TA, concerns only one study, the task model for the Roissy-Charles-De Gaulle (CDG) TWR (Courboulay & Kahn, 1996).

Unfortunately, this document reports only a very brief statement concerning the methodology used for the TA. The notation used for the analysis is matching the one used for the MANTEA project. Thus, it seems realistic that the same methodology was used for both the projects.

A limit of the document is the lack of an exhaustive description of the tasks, hindering their full understanding.

At the top-level of the tasks hierarchy, three main tasks were identified: 1) Monitor current situation; 2) Control moving objects; 3) Manage infrastructure. The graphs of the tasks are shown in Figure 22 and Figure 23.



Monitor displaysto visualize situation

to visualizemeteo

to monitorplanned aircraft to monitor meteo

Monitorcommunication channel

Tower control session

to monitorassume aircraft

STRIPBOARDPRIMARY RADAR

SECONDARY RADARMUST terminal

STRIPBOARDPRIMARY RADAR

SECONDARY RADARGROUND RADAR

PRIMARY RADARSECONDARY RADAR

GROUND RADAR

SATIR

to visualizemoving object

to assess trafficevolution

to assesssequence

to considereintersections

to consideretaxiing speed

to aquire current situationfrom previous Ctrl

to describe situationto next Ctrl

to manage infrastructure

o monitor current situation to control moving object

to assess conflict

to vizualizetaxiway

to visualizeRunway

to visualizespecial area

to monitor activemoving objects

to manage fequenceTo manage group

orungroup configuration

to coordinate withsupervisor

To coordinate withtower controller

to manageILS

to managelighting

to considererunway

to considerelevel

to consideretrajectory

Figure 22: CDG tower controller task Graph 1 (After Courboulay & Kahn, 996)



to control moving object

to manage strip to hand offmoving object

PENCIL

to determine

Acknowledgement

to handle activemoving object

VHF

Pilot call

Vehicule call

to identifymoving object

to assumemoving object

to assess trafficevolution

PENCIL

to determinelevel

to determineholding point

to determineline up

to modify SID

STRIPBOARD

to coordinatewith coordinator,tower, departure

to position strip

to issue instruction

to determineheading

to determinereport point

to determinepriority

to check strip to write on strip to modify strip

to hand off

to modify strip

to transmit strip

to determinespeed

Figure 23: CDG tower controller task graph 2 (After Courboulay & Kahn, 1996)



The following sub-sections provide more details about the first two tasks monitor current situation and control moving objects4.

1. Monitor current situation

According to the definition provided in the document, monitoring the situation means to create and update the mental model of the situation itself, and to create a mental list of control actions to perform. This is necessary in order for the ATCO to get and/or give information, to coordinate plans and issue instructions. This activity involves four sub-tasks:

Monitor the communication channels; monitor the displays, specifically: monitor planned A/C (through the strips, primary and secondary radar); monitor assume A/C (strips, primary, secondary and ground radar); monitor active objects (through the radar); monitor meteo (through the meteo display).

Assess traffic evolution. This task is composed of two sub-tasks. The first one entails the sequence assessment. The sequence is assessed by gathering information such as: traffic information (meteo, RWY and TXY congestion), moving objects, planned A/C, supervisor instructions. The arrival sequence is structured according to sequencing rules (which take into account the traffic situation, RWYs, wake vortex, climb rate, wind shear, speed, surface wind, etc.).

The other sub-task is the conflicts assessment. This task is carried out bearing in mind: 1) the intersections, taking into account: object position, wake vortex, breaking actions, blast, speed, report point, traffic situation, sequence and separation rules, supervisor instructions, heading, level; 2) the taxiing speed; 3) the RWY, taking into account the RWY occupancy and trying to anticipate possible conflicts; the ATCO should care about the position of the moving object, wake vortex, separation and sequencing rules; 4) the level, accounting for: SID, STAR, heading, level, moving object position, wake vortex; 5) the trajectory, taking into account: SID, STAR, heading, level, moving object position, and wake vortex.

The traffic situation is always observed and “visualized”, by looking at: TXY, RWY, special areas, moving objects and meteo. This set of tasks is usually carried out, by looking outside the window, if the meteorological conditions allow the visual scanning. The presence of the task visualize meteo among this group of sub-tasks might not necessarily imply the look out of the window (since meteo information is also provided in special displays). 2. Control moving objects

This activity refers to the control of A/C and vehicles on the RWYs. More in detail, the ATCOs are required to identify, guide, issue instructions to, and hand off A/C. This activity is related with five main tasks:

Identify moving object. The pre-requisite for this task is the call from the pilot (or the driver). Then, the controller has to look for the target object.

Assume moving object entails the “wakening” of a flight plan, after that, the ATCO is responsible of the A/C.

Handle active moving object. The pre-condition for this task is the assessment of the traffic evolution (cf. point about the Monitor current situation task). The two sub-tasks are issue instructions and determine.

4 The third task concerns more technical matters, like the management of frequencies, the lightning and other types of configurations.



The instructions (provided to the pilot) concern RWY instruction in progress, wake vortex, visual landing, holding point, threshold, ceiling, handoff, birds, surface wind, RVRs speed, level, SID, STAR, Beacon problems, ILS problems, FM interference on ILS, RWY inspection in progress, and others.

Concerning the determine task, the controller has to assess: speed, level, heading, the report point, the holding point, and the line up. Moreover the controller can decide about assigning priorities and about the modification of the SID. If the RWY is very congested, the ATCO may decide to assign a new RWY or a new trajectory to an A/C, negotiating –if necessary– with the GND or the supervisor.

Another set of tasks entails the management of the strip (checking the call-sign, SSR code, SID, slot time; writing instructions, take off, landing hour; position the strip, etc.). In addition, the controller has to perform hand-off tasks, specifically, handing-off A/C to the next unit, and/or handing over the strip.

6.3. INTEGRATING TASKS AND TASKS CHARACTERISATION

In 1988, the Computer Technology Associates performed a sophisticated study for the FAA. In a series of seven volumes all the operational concepts were analysed in order to understand how the controllers perform their operational jobs5 (Alley, Ammerman, Fairhurst, Hostetler & Jones, 1988).

The fifth volume was entirely dedicated to Control Tower. More precisely, the analysis focused on three main roles: the Tower6, the Ground and the Clearance Delivery position (this last role incorporates also the Flight Data, since, often, these two functions are combined together). The extent of the analysis was kept broad enough to capture all the relevant tasks; however, only FAA controllers were addressed by the study.

In the introduction of the volume, the authors state that the focus of the methodology is on the interaction between the controller and the automated system; but, when considered adequate for the scope of the study, also the tasks that do not entail such a type of interaction were presented.

Unfortunately, being the reports quite old, not all the volumes are available. For instance, Volume I (which describes more in detail the purposes of the study, the operational scenarios, and the methodologies used to carry out the study) is not accessible.

The fifth volume is articulated into three different reports that provide several types of information. The first report presents a TA description illustrated by graphs, whose notation is very similar to HTA. The remaining two reports provide a number of fine points and additional information about the tasks, defined «task characterisation analysis».

The volume is very large and difficult to deal with; thus, in order to present the summary of the results in an easier format, the data is herein summed up and displayed in the form of tables (which are not present in the original documents).

The Computer Technology Associates identified several categories of tasks for each position analysed. More precisely, the there are seven higher-level activities for the TWR and for Clearance Delivery/Flight Data positions, and six for the GND position. A general overview of the main results is reported in Table 1.

5

And how the tasks will evolve with the enhancements provided by the Advanced Automation System (AAS), which comprises automated capabilities to process and display data.

6 In the study, the actual definition of the Tower role is labelled Local control function (and not Tower). However, for practical reasons, in the present document we will refer to Tower controller or TWR.



Table 1: CT tasks in (Adapted after Alley et al., 1988)

TWR GND Clearance Delivery

Perform local7 situation monitoring

Perform ground situation monitoring

Perform clearance delivery/flight data situation monitoring

Resolve conflicts situations Control aircraft/vehicle ground movements

Route or plan flights

Manage air traffic sequences

Route or plan flights Manage air traffic sequence

Route or plan flights Assess weather impact Respond to flow constraints

Assess weather impact Manage ground controller position resources

Assess weather impact

Manage local8 controller position resources

Respond to system/equipment degradation

Manage clearance delivery/flight data controller position resources H

ig

he

r-

le

ve

l

ac

ti

vi

ti

es



HI MED LOW HI MED LOW HI MED LOW

181 125 42 68 114 21 30 81 13

Cr

it

ic

al

it

y

#

an

d

%

52% 36% 12% 32% 58% 10% 24% 65% 10%

6.3.1. Task Characterisation

At the bottom of Table 1, the tasks considered (expressed in figures and percentage) as having High (HI), Medium (MED) or Low (LOW) criticality are reported.

Every task was characterised according to a variety of properties, like frequency and criticality ratings, information sources, task type, cognitive/sensory attributes, performance requirements, etc. The information sources refer to the means used by the controllers to gather relevant information (console display, ATC mail, direct observation). The task types refer to the entry and receipt of information (e.g. entering data into the system; receiving data information by other means than by voice, like mail, system messages, and direct observation); analytical (data evaluation and assessment); and voice communication.

The highly critical tasks were further characterised in terms of two concepts: cognitive and sensory human attributes and performance requirements. Every attribute/requirement was associated with a task type.

7 TWR.

8 TWR.



More in detail, fourteen cognitive/sensory attributes, grouped by task type were identified. Each task type was associated to a performance requirement (for a total of twelve requirements), as illustrated in Table 2.

Table 2: Cognitive/Sensory attributes and performance requirements (Adapted after Alley et al., 1988)

Cognitive/sensory attributes Performance requirements

Task type: Entry

Coding Accuracy of Receipts

Implementation Time

Task type: Receipt

Movement Detection

Spatial Scanning

Filtering

Image/Pattern Recognition

Decoding

Accuracy of Receipts

Recognition Time

Task type: Analytical

Visualization

Short-Term Memory

Long-Term Memory

Deductive Reasoning

Inductive Reasoning

Mathematical/Probabilistic Reasoning

Prioritizing

Planning Time

Accuracy of Time Estimates

Accuracy of Spatial Estimates

Accuracy of Probabilistic Estimates

Appropriateness of Action

Appropriateness of Timing

Task type: Voice communication

Verbal Filtering Implementation Time

Accuracy of Communication

The task characterisation could provide the functional criteria to select the tasks that can be relevant for the future investigations of the AR project. For instance, the data summarised in Table 2 suggests that some of the tasks are related to visual issues (both in terms of performance criteria and cognitive/sensory attributes).

While the definitions of some cognitive/sensory attributes and performance criteria are straightforward, some others are not so obvious. For instance, the term visualization is too broad to be clearly placed within an operational series of tasks; the term filtering could refer to the ability of filtering out visual information that is not relevant; similarly, the definition accuracy of receipts may indicate whether a certain event is accurately identified and recognised by the controller but these remain speculations, as more explicit definitions are not available.



6.3.2. “Direct Observation”9 Tasks

For both the TWR and GND positions the tasks related to “direct observation” (as the main source of information) are here reported in Tables, in which all the information is given in a structured manner. However, despite the organisation, it should be realised that the tasks do not follow a strict labelling (some of these tasks are carried out contemporaneously, they can combine and overlap), and that the aerodrome settings are far more complex than a list of well-defined circumstances.

Most of the tasks reported in the tables are self-explained, in that, their definitions provide to the reader also the meaning of their labelling. Only the definition of the following tasks (which refer to the TWR) seem more ambiguous than the others:

1. Determine potential low altitude situation.

2. Observe A/C executing landing/option.

3. Conduct visual/radar identification of NORDO/overdue A/C.

6.3.3. TWR AND GND Tasks

The TWR tasks are summarised in Table 3, and the GND tasks in Table 5. All the tasks are organised according to the corresponding higher and middle-level activities10. The tasks were selected according to the criteria mentioned in section 6.3.1, that is the tasks are related to visual issues (both in terms of performance criteria and cognitive/sensory attributes).

The tasks characterisation is available for the highly critical tasks.

6.3.3.1. TWR and GND Tasks Characterisation

The Tables 4 and 6 summarise the sensory/cognitive attributes and the performance criteria (which are: accuracy of receipts, recognition time, and accuracy of spatial estimates). The Tables also report the estimated frequency of incidence of those tasks.

9 We deduced from the tasks description that the definition “direct observation” concerns the look outside. However, lacking a more extensive description of the terminology, the information herein reported should be carefully evaluated. 10 The definition middle level was not taken from the original work, but it is used here to provide an easier and more understandable

scheme of the hierarchical task description.



Table 3: TWR tasks related to direct observation (Adapted after Alley et al., 1988)

Higher Middle Tasks Criticality

Perform local situation monitoring Checking/evaluating separation Search airspace/movement areas to A/C asses separation High

Performing conflicts resolution Observe potential aircraft/vehicle conflict situation High

Performing minimum safe altitude separation Determine potential low altitude situation High

Performing airspace/ movement area violation resolution Observe potential airspace/movement area violation High

Observe A/C vehicle abnormality directly

Resolve conflicts situations

Issuing unsafe condition advisories Observe manoeuvres directly in response to advisory safety alerts

High

Processing deviations Perceive altitude/route deviation Observe ground traffic deviations directly High

Establishing departure sequence Observe aborted takeoff

Observe takeoff High

Establish landing sequences Observe A/C executing landing / option

Manage air traffic sequences

Monitoring non-controlled objects Observe directly an airspace / movement area intrusion by non-controlled object

Observe non controlled object in progress

High

Route or plan flights Responding to special conditions/emergencies Conduct visual/radar identification of NORDO (radio failure)/ overdue A/C High

Di

re

ct

o

bs

er

va

ti

on

Assess weather impact Responding to significant weather information

Observe weather area/ intensity ceiling/ base/ height/ movement/ visibility/ winds

High



Table 4: TWR tasks related to criticality level, information source, cognitive/sensory attributes and performance requirement (Adapted after Alley et al., 1988)


Frequency

Information source direct observation

Movement detection

Spatial scanning

Image/

Pattern recognition

Filtering Visualization Accuracy of spatial

estimates

Recognition time

Accuracy of receipts

High Search airspace/movement areas to A/C asses separation X X X X X X

Low Observe potential aircraft/vehicle conflict situation X X X X X X X X

Low Determine potential low altitude situation X X X X X X X X

High Observe potential airspace/movement area violation X X X X X X X

Low Observe A/C vehicle abnormality directly X X X X

Low Observe manoeuvres directly in response to advisory safety alerts X X X X X

Low Perceive altitude/route deviation X X X X X X

Low Observe ground traffic deviations directly X X X X X X

Low Observe aborted takeoff X X X

High Observe takeoff X X

Medium

Observe directly an airspace / movement area intrusion by non-controlled object X X X X X X

Low Observe non controlled object in progress X X X

Hi

gh

c

ri

ti

ca

li

ty

t

as

ks

Observe weather area/intensity/ceiling/ base/height/movement/visibility/winds X X X X X X X



Table 5: GND tasks related to direct observation (Adapted after Alley et al., 1988)

Higher

Middle

Tasks

Criticality

Establishing/maintaining positive A/C identification

Observe A/C/vehicle at reported position Observe A/C/vehicle progress through movement area

Perform ground situation monitoring

Checking and evaluating traffic movement Observe A/C/vehicle progress through movement area

High

Processing ground traffic deviations Observe ground traffic deviation directly High

Control A/C/ vehicle ground movement

Monitoring non controlled objects Observe directly a movement area intrusion by non controlled object Observe non controlled object progress through movement area

High

Route or plan flights Responding to special conditions/ emergencies Observe A/C vehicle abnormality directly High D

ir

ec

t

ob

se

rv

at

io

n

Assess weather impact Respond to significant weather information Observe weather area/ intensity ceiling/ base/ height/ movement/ visibility/ winds High



Table 6: GND tasks related to criticality level, information source, cognitive/sensory attributes and performance requirements (Adapted after Alley et al., 1988)


Frequency

Information source direct observation Movement

detection Spatial

scanning Image/

Pattern recognition

Filtering Visualization Accuracy of spatial

estimates

Recognition time

Accuracy of receipts

High Observe A/C/vehicle at reported position X X X X X X

High

Observe A/C/vehicle progress through movement area

X X X X X X X

Low

Observe ground traffic deviation directly X X X X X

Low

Observe directly a movement area intrusion by non controlled object

X X X

Low Observe non controlled object progress through movement area X X X

Low

Observe A/C vehicle abnormality directly X X X X X Hi

gh

c

ri

ti

ca

li

ty

t

as

ks

Medium

Observe weather area/ intensity ceiling/ base/ height/ movement/ visibility/ winds

X X X X X X



7. GENERAL DISCUSSION

This section provides a brief summary of the issues related to the view-out-of-the-window (as derived from the studies presented in the previous sections) and aims to preliminary define when the controllers look outside and what they look at.

7.1. OUTSIDE VIEW

The look outside is a recurring theme of all the studies herein reported. As stated in the document 4444 of ICAO (ICAO-4444, 2001): «Watch shall be maintained by visual observation, augmented in low visibility conditions by radar, when available». The role played by direct sight in tower tasks is not questionable.

7.2. MENTAL PICTURE AND TRAFFIC EVOLUTION

The outside view is an important source to capture information used for crucial processes, such as building up (at the beginning of the shift) and updating the mental picture, maintaining situational awareness, forecast traffic evolution (on a short-term basis, usually up to 5 minutes).

7.3. MONITORING

Monitoring is another task that, in all the studies, relates to the look outside and visual scan of the aerodrome area. Monitoring implies acquiring a “general overview” of the situation, but more active visual searches can be triggered by some events.

Alley et al. (1988) suggest that direct visual observation is also an opportunity to spot problems, e.g. perceiving the presence of abnormalities within the aerodrome (e.g. smoke, non-controlled objects intrusions, area violations).

7.3.1. Areas of interest

There is a distinction between the aerodrome areas of interests of TWR and GND, respectively the RWYs (and aerodrome airspace) and the TXYs. It is likely that more visual attention is directed toward these areas, in accordance to the controllers’ specific duties. The allocation of responsibility is defined by ICAO. The TWR is defined as being: «normally responsible for the operations on the runway and aircraft flying within the area of responsibility of the aerodrome control tower» (ICAO, 2001, p. 7-1). The GND controller is «normally responsible for traffic on the maneuvering area with the exception of runways» (op. cit., p. 7-1).11 This differentiation is also mentioned in (Rossi et al., 1996b) and (Alley et al., 1988). However, the tasks are not ‘rigidly’ separated and we cannot exclude an overlapping between the two areas of interest.

7.3.2. Checking clearances

Rossi et al. (1996b) mention two interesting tasks, which entail both TWR and GND: issuing and visually checking the clearances (cf. 6.2.1.1 and 6.2.1.2, assist/act on A/C).

11 Mine italic.



The TWR issues takeoffs and landings clearances and visually checks their correct execution (observing landings and takeoffs, cf. Table 3) or the deviations from the issued instructions (cf. 6.2.1.1). A pre-requisite for the execution of landings and takeoffs is the verification of the RWY’s status (occupied or vacated) and the presence of possible incursions (cf. 6.2.1.1).

The GND issues push-back and taxiing instructions. A pre-requisite for these tasks is maintaining the positive identification of the A/C (cf. Table 5 and 6.2.2) then, the correct execution of the instructions is visually checked (cf. 6.2.1.2). In addition, the GND monitors the A/C movement progressing through the movement area, checking for deviations from the issued instructions (cf. 6.2.1.2 and Table 5).

7.3.3. Operational experience

Dittman et al. (2000) state that controllers know the most critical parts where possible conflicts are more likely to occur (cf. 6.1.2.3). They also give another hint (cf. 6.1.4.1) about what and where controllers may look at: A/C in holding or waiting for departure on the runway. Courboulay and Kahn (1996) mention additional elements: report points, holding point, points of intersection (intersecting RWYs, TXYs or both) and special areas (cf. 6.2.1.2).

The meaning of ‘special areas’ is unclear. Perhaps, every airport has some special districts that, for local reasons (e.g. dense movement of vehicles?), the controllers are more likely to visually verify.

7.4. SAFETY AND CONFLICTS

All the studies herein summarised relate the outside view to highly critical tasks like the detection and the resolution of potential conflicts. These tasks may occur at two levels. On the one hand, potential threats to safety may occur in the aerodrome airspace. Safety assessments are performed taking into account A/C positions (flight levels and trajectories) and wake vortex separations (cf. 6.2.2). The A/C category and its performance (hence type and speed) are important characteristics for the assessment.

On the other hand, potential conflicts may occur on the ground, between A/C and between A/C and other vehicles. Sections 6.1.2.3 and 6.2.2 provide a number of elements that have to be considered for this task: type of A/C, performance, speed, braking action, A/C category (for wake vortex and blast) and (accuracy of) reported points (that can be visually verified as compliant/deviating with/from the instructions).

It should be remarked that some of these characteristics are not directly available by looking outside (e.g. A/C type and category are marked on paper strips). Thus, the outside view is necessary, but may not be sufficient. However, it is probable that the controllers are able to make assessments on the basis of their experience (e.g. recognizing ‘at glance’ the type and the category of an A/C, making estimations about its speed and performance, etc.).

7.5. VERBAL COMMUNICATIONS

Another remark concerns monitoring the communication channels (cf. 6.2.2) and monitoring read-back (cf. 6.1.2.4), which includes auditory information. For example, in low visibility conditions, the ATCOs check A/C positions through the verbal reports of the pilots. This information -although not visual- provides the controllers with spatial data12. Potential problems can be identified -not only by

12 In more general terms, the interaction effects between visual and auditory information deserves some attention.



looking outside but also- if the read back is not correctly executed and probably by paying attention to the intonation and prosody of the pilots’ read-back.13

7.6. TRUST AND TIME

According to Dittman et al. (2000) trust toward pilots is a supplementary element taken into account by the controllers. Trust is built on past knowledge and personal experiences and it seems to contribute to important decisions (e.g. letting an A/C taking off between two landings, cf. 6.1.2.3).

Another constraint for the aerodrome controllers is time employed to take decisions. Traffic must be expeditiously managed, it can change rapidly and, according to the changes, also the decisions have to be taken in an instantaneous manner, especially when the volumes managed are dense. The aerodrome controllers process information in a bottom-up manner, mainly driven by contingent events, external inputs, etc. The identification and resolution of potential conflicts is the highest priority task, and the controllers are demanded to act particularly quickly; no time is left for long term planning14.

7.7. VISIBILITY

Something that did not emerge from the studies is how the controllers manage the traffic in low visibility conditions. According to ICAO, the appropriate ATS authority shall establish the appropriate provisions for operations under low visibility conditions (ICAO-444, 2001) (e.g. the local ATS shall specify the longitudinal separation on taxiways15), and that watch should be augmented in low visibility conditions by radar (when available).

Thus, the procedures and the rules followed in low visibility conditions are tailored to the specific characteristics of the aerodrome. Probably, the study of this topic requires an ad hoc investigation that takes into account context-specific factors (such as the airport configuration, the devices available in the tower, etc.).

7.8. COLLABORATION BETWEEN CONTROLLERS

It was mentioned in section 6.2.1.1 that communication and coordination are usually done between the TWR, the GND and the supervisor, and also with the adjacent unit. However, more extensive explanations about how and why controllers communicate (and eventually collaborate) are not available in the works herein reported.

In general, task analysis takes the individual as the main unit of analysis. The description of the way the controllers coordinate and collaborate could be better described with a more holistic framework, such as AT (cf. 3.4); AT can provide a theoretical reference to gain insights on the cooperative aspects of the tower, and give a more “realistic picture” of the tower activity as a whole.

13 This example was given by Ray Dowdall, during a discussion on ATC. As he said, intangible things can provide a lot of information to

controllers. 14 It is not surprising, then, that during the shift change the controllers won’t take over the controlling position if potential threats to

safety are recognised. 15 ICAO, op. cit., p. 7-11.



8. REFERENCES

1. Alley, V.L., Ammerman, H.L., Fairhurst, W.S., Hostetler, C.M., Jones, G.W., (1988). FAA Air Traffic Control Operations Concept. Volume 5. ATCT/TCCC (airport Traffic Control Tower/Tower Control Computer Complex) Tower Controllers), Computer Technology Associated INC. Colorado Spring CO, DOT FAA AP/87-01.

2. Annett, J., Duncan, K., Stammers, R., Gray, M., (1971). Task Analysis, HMSO, London.

3. Annett, J., Duncan, K., (1967). Task Analysis and Training Design, Occupation Psychology, 41, 21-221.

4. Bergé, P., (2005). Initial EMMA Air-Ground Operational Service and Environmental Description (OSED Initial), Document No. D1.3.1, Eurocontrol.

5. Callan, K., Siemieniuch, C., Sinclair, M., Rognin, L., Kirwan, B., Gordon, R., (2005). Review of Task Analysis Techniques for use with Human Error Assessment within the ATC Domain. Available at: http://www.eurocontrol.int/eec/public/standard_page/safety_doc_task_analysis_and_atm.html

6. Choroba, P., (2004). Personal communication.

7. Collins Cobuild English Language Dictionary, (1988). Collins Birmingham University, London & Glasgow.

8. Courboulay, M., Kahn, J., (1996). ATHOS CDG Airport Tower Controller Task Analysis, WP3, ATHOS/SOF-TEC-W3-006-R1, TR 1005, Telematics Application Programme (Transport/Air).

9. Daniels, H., Brown, S., Edwards, A., Leadbetter, J., Martin, D., Middleton, D., Parsons, S., Popova, A., and Warmington, P., (2005). Studying Professional Learning for Inclusion, New Learning Challenges: Going beyond the Industrial Age System of School and Work, Yamazumi, K., Engeström, Y. and Daniels, H. Kansai (Eds.), Kansai University Press.

10. Dittmann A., Kallus K.W., Van Damme, D., (2000). Integrated Task and Job Analysis of Air Traffic Controllers – Phase 3: Baseline Reference of Air Traffic Controller Tasks and Cognitive Processes in the ECAC Area, HUM.ET1.ST01.1000-REP-05, Eurocontrol.

11. Endsley, M. R., (1990). A methodology for the objective measurement of pilot situation awareness, in Situation Awareness in Aerospace Operations (AGARD-CP-478), Neuilly-sur-Seine, France, Advisory Group for Aerospace research and Development.

12. Endsley, M.R., (1997). The role of situation awareness in naturalistic decision making, C.E. Zsambok and G. Klein (Eds.), Naturalistic decision making, Erlbaum, p.269-283.

13. Engeström, Y., (1999). Innovative learning in work teams: analysing cycles of knowledge creation in practice, Perspectives on Activity Theory, Y. Engeström, R. Miettinen, R.L. Punamäki (Eds), Cambridge University Press.

14. Engeström, Y., (1987). Learning by expanding: An activity-theoretical approach to developmental research. Helsinki, Orienta-Konsultit.

15. Engeström, Y., (2004). Personal communication.

16. Fields, B., Amaldi, P., Tassi, A., (2003). Representing collaborative work: The Airport as Common Information Space, Technical Report IDC-TR-2003-003.

17. Heizer, J., Render, B., (1999). Operation Management, Upper Saddler River, Prentice-Hall.

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9. ACKNOWLEDGMENTS

I would like to thank Marc Bourgois and Patrizia Marti for providing useful comments and feeback.

http://www.marxists.org/archive/vygotsky/works/mind/ch01.htm

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