Aim To introduce the Concept and Fundamentals of Visual Navigation

Fundamentals of NavATC Chapter 1

Aim

To introduce the Concept and Fundamentals of Visual Navigation

Objectives1. Define “Visual Navigation and Dead Reckoning

Navigation”2. Describe the “Form of the Earth”3. Identity our position, the direction we wish to

travel and the distance we want to fly4. Describe and calculate our air speed and velocity

through the air5. Calculate and describe our altitude above the

surface of the Earth

1. DefinitionsVisual Navigation is fun, challenging and very

satisfying if done properly.

Australia can be characterised as follows• A sparse population with our capital and other major cities

concentrated along the coast, principally in the eastern states• Many towns on charts are very small

and easy to confuse with other towns• A lack once away from the coast of

easily recognisable land features due to the generally flat terrain and lack of trees, vegetation, rivers or other easily distinguishable features especially as you move further inland

• There are few Navigation Aids such as a VOR or NDB as you move further inland

1. Definitions

How to successfully navigate your way around Australia

1. Understand the concepts and principles involved in Visual Navigation

2. Plan your flight carefully before you depart

3. Be organised and disciplined in your approach in flight to navigating from your take off point to your destination

4. Be “ahead of the aircraft” by which we mean anticipating what needs to be done in the next few minutes and calculating contingencies to cope with unexpected events

1. Definitions

Visual Navigation is where pilots use aviation charts (maps) to match observed ground features to determine the position (fix) of the aircraftVisual Navigation is based on a pilot:• Being able to sight sufficient ground features be able to fix the

position of the aircraft at not less then 30 minute intervals

Visual Navigation

• Navigation Aids such as a GPS, VOR, NDB may be used to assist in determining the position of the aircraft but the prime means of navigating is by Dead Reckoning

Dead Reckoning (DR) is the process of calculating one's current position by using a previously determined position, or fix and advancing that position based upon known or estimated speeds over elapsed timeDead Reckoning is based on a pilot:• Flying accurately the Headings (HDG) which have been previously

calculated• Knowing the elapsed time flown since the last known position• Being able to closely estimate the achieved Ground Speed (GS)• Accurate chart (map) reading to initially identify your position based

on time elapsed and then confirming your position by reference to ground features

1. DefinitionsDead Reckoning

2. Form of the Earth

The Earths shape can be described as an “oblate spheroid”It is flattened at the Poles, the surface is constantly changing due volcanic, seismic and tidal activityFor practical navigation purposes we can describe the earth as a perfect sphereThe Earth rotates eastward on its Polar AxisThe 2 points where this axis meets the surface are the North and South Geographical Poles (True North or True South)

Shape and Movement


A Great Circle is a circle drawn on the surface of the Earth with a plane that passes through the centre of the EarthExamples include:

• Meridians of Longitude• The Equator• Horizontal Paths of Radio Waves

A Great Circle divides a sphere into equal partsA Great Circle is the shortest path between 2 points on the surface of a Sphere such as the Earth

Great Circles

http://en.wikipedia.org/wiki/File:Great_circle_hemispheres.png


A Small Circle is a circle drawn on the surface of the Earth that is not a Great CircleThe centre of a Small Circle is not at the centre of the Earth

Small circle of a sphere

Small Circles

http://en.wikipedia.org/wiki/File:Small_circle.svg


In navigation, a rhumb line is a line crossing all meridians of longitude at the same angleOn a plane surface this would be the shortest distance between two points.Over the Earth's surface at low latitudes or over short distances it can be used for plotting the course of a vehicle, aircraft or shipFor practical purposes a Great Circle direction and a Rhumb Line direction may for distances under 200 nm be considered the same.

Image of a rhumb line, spiralling towards the North Pole

Rhumb Lines

http://en.wikipedia.org/wiki/File:Loxodrome.png


All Great Circles containing the Polar Axis are “Meridians of Longitude”The prime meridian, based at the Royal Observatory, Greenwich in the UK, was established by Sir George Airy in 1851Meridians of Longitude are specified by their angular difference in degrees East or West of the Prime MeridianThe Prime Meridian is either 0° if on the Atlantic side of the Earth or 180° degrees if on the Pacific Ocean side of the EarthIf you divide 360° by 24 hours, you find that a point on Earth travels 15° of longitude every hour

Longitude



Lines of constant latitude, or parallels, run east–west as circles parallel to the equatorLatitude is an angle which ranges from 0° at the Equator to 90° (North or South) at the poles

Latitude


3. Position, direction and distance

Latitude is used together with Longitude to specify the precise location of features on the surface of the EarthBy convention a position is reported in the following format;

• Latitude in Degrees, Minutes, Seconds, N or S of Equator

Followed by

• Longitude in Degrees, Minutes, Seconds, W or E of the Prime Meridian

Seconds can be replaced by decimal parts of a minute eg 6 Seconds = 0.1

Position Fixing

Direction is the angular position of one point to anotherWe need a datum point to establish a reference point and for our purposes we use a North-South Line through our current position (local meridian)By convention we use a flat circle divided into 360 degrees to refer to specific Headings (HDG) to our destination

Direction



The 4 Cardinal Points are;

North as 000, South as 180, East as 090, West as 270

In between are all the other points of the compass

A HDG of 300 is where on the diagram?

A HDG of 115 is where on the diagram?

Describing Direction



Our initial reference point for calculating the HDG to fly is True North or the North Geographic Pole

This makes it easy to measure angles and plot and measure tracks on our Navigation Charts

However we normally do not have an instrument in our aircraft that can display our HDG relative to True North

True North



We have in our aircraft a compass that can display our HDG relative to Magnetic NorthThe Iron Core of the Earth acts as a huge magnet with the 2 magnetic poles being Magnetic North and Magnetic SouthCurrently the Magnetic North Pole lies in Hudson's Bay, Canada and it is currently moving toward Russia at between 55 and 60 km per yearThe difference between True North and Magnetic North is the Magnetic Variation and varies depending on the location of your aircraft

Magnetic North

Movement of Earth's North Magnetic Pole across the Canadian arctic, 1831–2001



Illustration of the Magnetic Field of the Earth



Navigation Charts display lines of equal Magnetic Variation, called IsogonalsWe adjust our planned True HDG to a Magnetic HDG by allowing for the Magnetic Variation to give us the Magnetic Track (TR) we need to follow to arrive at our destination

Magnetic Variation

Variation is labelled east or west depending on whether the Isogonal is east or west of the Agonic Line (zero magnetic variation)

If variation is East, magnetic direction is less than trueIf variation is West, magnetic direction in more than true

(East is least, West is best)



Magnetic deviation refers specifically to compass error caused by magnetized iron within a ship or aircraft. This iron has a mixture of permanent magnetization and an induced (temporary) magnetization that is induced by the Earth's magnetic field. To calculate the magnetic deviation for an aircraft compass is “swung” at regular intervals using specific procedures.

Magnetic Deviation

The outcome is a calibration chart which is displayed on or by the compass. The deviation is generally minor , less than 2 degrees.



For Navigation we use Nautical Miles to measure distances1 Nautical Mile (nm) is the length, at the Earth's sea-level surface, of one minute of arc of a great circleThe International Nautical Mile is 1,852 metres or 6,076.1 feetConsequently, one degree of latitude (measured along a meridian) has an equivalent surface distance of 60 nautical miles

For other Horizontal Distances we use Kilometres or Metres, for example Runway length, visibility, horizontal distance from cloud

For Vertical Distances we use Feet, for example Altitudes to fly and vertical separation from clouds

Distance Measurement


We fly in a mass of air that will move in accordance with the direction of the wind and its velocity.To accurately navigate we need to understand how the wind affects the path and speed of our aircraft over the ground.The 4 speeds we are interested in are:

• Indicated Airspeed (IAS) • Calibrated Airspeed (CAS)• True Airspeed (TAS)• Groundspeed (GS)

Speed

4. Calculate Air speed and Velocity

Our Airspeed Indicator (ASI) in the C172 compares the total pressure measured by the Pitot Tube of the air due to its movement relative to the aircraft with the static pressure measured by the Static Vent.

Total Pressure – Static Pressure = IAS

The reading you obtain from the ASI is affected both by the speed and the density of the air.

For manoeuvring the aircraft we use IAS as displayed by the ASI. For example flap limiting airspeeds and approach airspeeds

Indicated Airspeed



Our Airspeed Indicator (ASI) in the C172 is subject to 2 types of errors;Instrument ErrorThis type of error is a result of friction within the instrument and/or bad design.

Position ErrorThe location of the Pitot Tube and the Static Vents are critical to the accuracy of the ASI. Incorrect positioning may lead to errors when the airflow in the vicinity of the Pitot Tube and Static Vents is disturbed for example by lowering flaps.

Calibration TableThe ASI is “calibrated” and the results are used to provide a Calibration Table for pilot use to aid in interpreting the ASI. In practice the errors are very small and we can generally assume IAS = CAS

Calibrated Airspeed



For navigation purposes we need to be able to calculate the effect of changes in air temperature and air pressure on our speed through the air. Once calculated this gives us our True Airspeed (TAS)The ASI is calibrated in accordance with the international standard sea level atmosphere. Changes in the air density (temperature and pressure) will mean that the ASI does not display the TAS.

Temperature ChangesThe warmer the air the less dense it is. Which means the aircraft must travel faster through the air to maintain the same IAS, therefore TAS is higher.

Pressure ChangesAs we gain altitude there are less molecules of air and therefore the air is less dense. Which means that as we gain altitude we will have a lower IAS for the same TAS.

True Airspeed


The G1000 calculates and displays our TAS (below the IAS indicator).We can however manually calculate the TAS with our Flight Computer.We do that by reference to the Outside Air Temperature and the Pressure Altitude.TAS will always be higher than IAS.

Calculating True Airspeed



A Velocity is a rate of change of position in a given direction and is therefore a combination of both speed and direction.The speed and direction of an air mass is a velocity.By convention wind speed and direction is provided in the following format;

• Direction (3 digits)/ Speed (2 or 3 digits)

ExampleA wind of 20 knots travelling from the north would be expressed as 360/20

Wind Velocity



Weather reports will provide wind information in the following format

Degrees MagneticFor surface winds eg for take off or landing in an ATIS or TAF

Degrees TrueFor navigating through an air mass in an ARFOR

This means that we must adjust the winds we use in navigating from one place to another to take into account the Magnetic Variation.

See the Bureau of Meteorology – Aviation section for detailed information on aviation weather reporting.

www.bom.gov.au

Weather Reports


http://www.bom.gov.au/


The GS is one of the most important pieces of information a navigator needs to accurately fly to your destination.

GS is found by adjusting your TAS for the effect of wind (direction and velocity).

ExampleTAS = 120 knots, HDG = 360, Wind = 360/25 Calculation – 120 knots – 25 knots of wind = GS of 95 knots

(As there is nil cross wind the calculation is simple. We will try more complex examples using the Flight Computer to calculate our GS in future lessons)

Groundspeed



We use the GS to calculate a TI which in turn dictates your fuel requirements, the time you will arrive and the payload you can carry.We can check our GS as the flight progress by comparing the time it takes to fly over 2 known points with the distance actually travelled.

ExampleDistance travelled between Alpha and Bravo = 90nmTime Interval to travel between Alpha and Bravo = 45 minutesGS = 90/45 or 2nm per minute therefore GS = 120 knots

Time Intervals



The Triangle of Velocities is typically used to calculate HDG and GS

In order to use the triangle we must know at least two of the following:

• Track (TR) and Groundspeed (GS)• Wind (Direction and Strength)• Heading (HDG) and True Airspeed (TAS)

Track and Groundspeed

Heading and True AirspeedWind

Triangle of Velocities



Unlike driving a car when flying we operate in a 3 dimensional environment and we need to have some way to navigate both horizontally and vertically

Terrain Separation: We need to ensure we know where we are in relation to the ground to ensure a safe flight to our destination

Traffic Separation: We need to have a common system of determining our altitude to ensure separation from other aircraft

Aircraft Performance: How high or low we fly will affect aircraft performance and how efficiently we can get to our destination

5. Altimetry Vertical Navigation


5. Altimetry

Altitude: Measured by reference to Mean Sea Level (MSL)For example at Parafield we fly our circuit altitude is 1,000 feet Above Mean Sea Level (AMSL) so all aircraft are at the same AltitudeHeight: Measured by reference to a point above the groundFor example if we were flying above Mount Lofty at an altitude of 3,500 feet we would be at a height of 727 feet above Mount LoftyFlight Level: Measured by reference to a common pressure datum of 1013.2 hPaFor example above 10,000 aircraft set 1013 hPa on their Altimeters and fly at “flight levels” such as FL 150 (15,000 feet)

Vertical Measurement

GroundSea

HeightAltitude


5. Altimetry

QNH: Setting the Altimeter to a specified QNH will indicate aircraft Altitude (AMSL)

QFE: Setting QFE (Field Elevation) will determine the altitude above the ground

Note: QFE is normally only used in some recreational aviation activities such as aerobatics or parachuting

ISA Pressure: The International accepted standard pressure at sea level is “1013.2 hPa”

This is used to establish “flight levels” for aircraft flying at high altitude, for example in Australia above 10,000 feet, in the USA above 18,000 feet

Altimeter Settings


5. Altimetry

We set the actual pressure or “QNH” before take off as the actual pressure is seldom the same as the ISA standard of 1013.2.

Setting the QNH on the Altimeter sub scale will provide the pilot with the actual altitude of the airfield and in flight the altitude of the aircraft AMSL.

Pressure ChangesDuring the day the actual pressure will change and according the actual QNH will change.

Pressure changes are advised in aviation weather forecasts, by ATC and by an airfield ATIS.

If we are on the ground we can determine the QNH by setting the known airfield height above mean sea level and reading the QNH off the altimeter sub scale.

QNH Settings


VFR Hemispherical Altitudes Below 10,000 Feet

Magnetic Tracks 000 - 179 180 - 359

Cruising Altitudes(Area QNH)

1,5003,5005,5007,5009,500

2,5004,5006,5008,500

Hemispherical Cruising Altitudes are optional below 5,000 feet however it is recommend that wherever possible hemispherical altitudes should be flown

Why is it important to fly at the correct altitude?

IFR aircraft fly at Evens or Odds Altitudes

Selection of Altitudes5. Altimetry


VFR Hemispherical Cruising Levels Above 10,000 Feet

Magnetic Tracks 000 - 179 180 - 359

Cruising Levels(1013 hPa)

115135155175195

125145165185

FL 115 is not available when the Area QNH is less than 997 hPaFL 125 is not available when the Area QNH is less than 963 hPa

Oxygen is required for flight above 10,000 feet.

VFR flight is prohibited above 20,000 feet.

Selection of Cruising Levels5. Altimetry

Questions?

Documents

Aim To introduce the Concept and Fundamentals of Visual Navigation