1

Airborne spacing in the terminal area:A study of non-nominal situations

EUROCONTROL Experimental Centre

European Organisation for the Safety of Air Navigation

2

Starting point

Motivation Improve the sequencing of arrival flows

through a new allocation of spacing tasks between air and ground

Neither “transfer problems” nor “give more freedom” to pilots … shall be beneficial to all parties

Assumptions Air-air surveillance capabilities (ADS-B) Cockpit automation (ASAS)

Constraints Human: consider current roles and working methods System: keep things as simple as possible

Paris Orly, 2002, source: ADP

3

Context (1/3)

Development and refinement of spacing instructions and working methods Flight crew tasked by the controller to achieve then maintain a given

spacing to a designated aircraft No modification of responsibility for separation provision New “spacing” instructions – not separation, not clearance

Remain

Adjust speed

To maintain current spacing

Merge

Adjust speed

To maintain predicted spacing

Vector then merge

Initiate direct then adjust speed

To achieve then maintain spacing

4

Context (2/3)

Identification of required functional evolutions (air and ground) and route structure

Aircraft under spacing

Aircraft with target selected

5

Context (3/3)

Assessment of feasibility, benefits and limits Representative environment with very high traffic From cruise to final approach Controller, pilot and system perspectives

BaselineWith spacing

Distribution of inter aircraft spacing at final approach fix

9060 120 150 180

Num

ber o

f airc

raft

22

23

24

25

26

27

Baseline

Number of aircraft passing final approach fix

(period 45min)

With spacing

Flown trajectoriesBaseline

Flown trajectoriesWith spacing

6

From past to present

However, everything was in nominal conditions…

A series of prototyping sessions was conducted to investigate the use of airborne spacing under non-nominal conditions Feasibility and definition rather than data collection Focus on terminal area Situations investigated

Mixed ASAS equipage Holding patterns Unexpected events (go-around, emergency, radio failure,

spacing instructions not correctly executed)

7

Experiment setup

Generic TMA with two or three entry points feeding a single landing runway

Traffic close to maximum landing capacity: 36 - 40 arrivals per hour with 20% heavys

Departures not simulated but strategically separated

Two controller positions Approach (“initial”, “pick up”) Final director (“intermediate”, “feeder”)

8

Application to terminal area

With spacing instructions (as defined), integration achieved on a point and aircraft shall be on lateral navigation

How to integrate flows of aircraft with airborne spacing? How to delay or expedite aircraft under airborne spacing?

Today (Paris Orly, 2002, source: ADP)

9

Specific route structure

FAF

IAF IAF

Merge point

Sequencing legs at iso distance for path shortening or stretching

(vertically separated)

Envelope of possible paths

To expedite or delay aircraft while remaining on lateral navigation

10

Typical airspace

BOKET

CODYN

LOMAN

MOTEKODRAN

OKRIX

KAYENLAURIRADON

REDKO

PONTY

ZABOU

FAO26

EPERN

GOVINMORET NASIG

BOKET

CODYN

LOMAN

MOTEKODRAN

OKRIX

KAYENLAURIRADON

REDKO

PONTY

ZABOU

FAO26

EPERN

GOVINMORET NASIG

PONTY/MOTEK FL100ODRAN/KAYEN FL080EPERN/GOVIN FL060ILS 4000

11

Mixed equipage

12

Mixed equipage

ASAS 100% ASAS 50%

LevelSpeedDirect/headingSpacing

Manoeuvre instructions

ASAS 0%ASAS 100%ASAS 100% ASAS 50%ASAS 50%

LevelSpeedDirect/headingSpacing

LevelSpeedDirect/headingSpacing

Manoeuvre instructions

ASAS 0%ASAS 0%

ASAS 100%ASAS 50%ASAS 0%

Inter aircraft spacing at final approach fix

907050 110 170130 150

ASAS 100%ASAS 50%ASAS 0%

Inter aircraft spacing at final approach fix

907050 110 170130 150

14

Holding patterns

15

Holding patterns

A holding stack defined for each IAF Stacks located upstream from each leg Two flight levels for each sequencing legs

Receiving aircraft from holding and airborne spacing for final integration found feasible and comfortable

Traffic from holding very homogeneous Lack of accurate knowledge of aircraft actual exit of holding

patterns forces delay in sequence order identification ASAS and its associated route structure found very effective to

remove holding induced variability

16

Go-around

17

Go around

Go-around occurred while in contact with tower

Handling found not more difficult than with current practices Easy identification of where to re-integrate the aircraft

Standard procedure defined Re-joining of one IAF May require cancelling spacing instructions and setting new ones Possible re-integration before the IAF (track parallel to the sequencing

legs)

18

Emergency

19

Emergency

Emergencies declared before the IAF

Situation found not more difficult than today Speed difference vs. position in sequence Key steps

Integration position decision Gap creation

Vectoring Sequencing legs

The emergency shall not be used as a target A “merge at least” may be issued for the emergency in case catching up the

preceding aircraft Early speed reductions in upstream sectors to aircraft after the emergency

20

Radio failure

21

Radio failure

Standard radio failure procedure defined

Radio failure occurred before IAF

Situation found not more difficult than today Early descent while on leg could create problems Overall same techniques as for emergency but with more

margins due to un predictability of aircraft

22

Incorrect spacing instructions

Aircraft (under spacing) catching-up with its target Situations were not rated as serious cases by controllers Typical recovery procedure

“cancel spacing” along with a speed reduction if appropriate re-select target (when not retained) and re-issue spacing instruction (generally “merge”)

Worse case to be handled like a go-around

“Continue heading then merge” correctly read-back but executed as “merge” Mistake detected quickly and found easy to handle by controllers Typical recovery procedure

“cancel spacing, retain target” with speed (generally 220kt) to “non compliant” aircraft

vector the aircraft on a track parallel to the sequencing legs new spacing instruction (generally “continue heading then merge”)

23

Summary

Mixed equipage Feasible Reduced workload and communications scalable Non equipped aircraft required more monitoring

Holding patterns Airborne spacing for final integration found feasible and comfortable

Unexpected events Less difficult than initially anticipated Similar to today’s operations Go-around, emergency and radio failure

Identification of re-integration location is key point Spacing instructions not correctly executed

Not rated as serious: quickly detected and easy to handle General principle

to “isolate” the aircraft experiencing the problem (i.e. take it out of the sequence) not to act on the whole sequence

24

A new RNAV route structure?

A preliminary step to prepare implementation of airborne spacing

A transition towards extensive use of P-RNAV

A sound foundation to support further developments such as CDA (continuous descent) and 4D (target time of arrival)

Beyond (or before)…

0

20

40

60

80

100

120

0 10 20 30 40 50 60

Altit

ude

(feet

x10

0)

Distance to final approach fix (NM)

Baseline

New route structure

0

20

40

60

80

100

Final

Freq

uenc

y oc

cupa

ncy

(%) New route structure

Baseline

Approach