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7.5.2 Pilot Navigation

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Principles of Plotting

Plotting is a process of recording on a chart, information about the progress of an aircraft in flight in such a way as to enable the navigator to solve the triangle of velocities upon which navigation is based.

Plotting Instruments

The plotting instruments you will need are:

  • The protractor for the measurement and plotting of bearings.
  • Dividers for the measurement and laying off of distances.
  • Compasses for plotting DME position lines
  • A straight edge.
  • The navigation computer.

Plotting Symbols

Conventional symbols are used in plotting as illustrated below.

In practice there are two main forms of plot, the track plot and the air plot.

The Track Plot

The track plot is probably the simplest form of plotting. The position of the aircraft, as determined by fixes or as calculated from knowledge of the aircraft’s track made good and ground speed, is plotted at intervals on the chart. These positions are used to determine the:

  • Aircraft’s progress.
  • To calculate future positions.
  • To calculate estimated time of arrival
  • To calculate any corrections of heading that may be necessary.

Typical Trackplot

In the above trackplot an aircraft plans a course between A and B

  • 1100 The aircraft leaves A.
  • 1130 A pinpoint is taken.
  • 1200 A second pinpoint is taken.

From these pinpoints we can calculate:

  • Track.
  • Groundspeed.
  • Wind Velocity.

At 1210 a DR position is plotted using the information above, this is a position the pilot navigator can calculate.

  • The pinpoint at 1200 gives us a definite position.
  • We know the track we are flying and the groundspeed.
  • If we project our track for 12 minutes at 1212 we will be at the DR position
  • A new track required to B can be drawn.

If we calculate a wind velocity, we can then work out a new heading and groundspeed to fly to B.

The time interval between fixes selected for the determination of track, ground speed and the wind velocity is critical. It must not be too short and it must not be too long. In ground speed:

  • Measurement of fixing errors is magnified when the time interval is too short.
  • When the time interval is too long the ground speed obtained becomes too much of an average.

The ideal time interval used in measurement of track and ground speed should be at least 20 and not more than 40 minutes.

Air Plot

One of the main disadvantages of the track plot is that the system is inflexible. Using the track plot, DR calculations of ground speed and track are only possible when no alteration has been made in heading and TAS during the run between fixes. No such limitations occur when using the alternative method of plotting called the air plot.

When keeping an air plot the navigator lays off from his point of departure a vector representing the true heading and airspeed for the appropriate time of flight. He can then estimate the position of the aircraft neglecting wind effect (such a position is known as an air position). In the event that either heading or TAS is subsequently changed he can continue to plot vectors of heading and TAS to establish subsequent air positions of the aircraft for each time that a change takes place.

Eventually when a fix is obtained the navigator will have both air position and ground position of the aircraft plotted for the same instant of time. The vector joining them will give the wind velocity for the appropriate period of time since the air plot was commenced. Wind velocity found by this method is known as an air plot wind velocity. Like the track and ground speed wind velocity there is an ideal interval of time over which it should be determined and for similar reasons this ideal interval is between 20 to 40 minutes.

In the above plot the heading and TAS are plotted. Each time the aircraft changes heading the new heading and TAS are then plotted.

One of the greatest advantages of the air plot is that however often alterations of headings and air speed are made, the navigator can keep a record of his air position which he can use to establish a DR position by plotting an appropriate amount of wind velocity from the air position.

Restarting the Air Plot

To avoid having to draw very long vectors for wind velocity, which will be both cumbersome and inaccurate, an air plot must not be allowed to run indefinitely, but, should be restarted from fixes at convenient intervals. It is imperative that only accurate fixes are used for restarting an air plot, as any error in the initial fix will be carried through the whole plot. Under no circumstances should an air plot be restarted from a DR position, as this would only perpetuate any errors already present.

Establishment of Position

The two methods of plotting, the track plot and the air plot have been described above. In each case it was assumed that the ground position of the aircraft could be determined. This section is devoted to the methods of determining position.

DR Position

DR position, which is the calculated or deduced position of the aircraft may be determined by either track plot or air plot.

Track Plot Method

There are two methods of determining DR position by track plot:

Mean Track Made Good

Track is established by drawing the mean track through the fixes. The distance run between an optimum pair of fixes calculates groundspeed and a future position of the aircraft is calculated.

Having determined track and ground speed from the application of known W/V to TAS and heading the track is drawn in from the last known position and the distance covered since that position is laid off to give the new DR position.

Air Plot Method

In this method a full graphical record of headings and TAS is maintained. The DR position can then be determined for any time by applying the appropriate amount of wind velocity.

Fixing

Fixes are precise observations of the aircraft’s position.

Position Lines

It is not always possible to determine the position of the aircraft precisely. A common situation is to be able to determine a line along which the position of the aircraft is known to lie; such a line is called a position line.

Sources of Position Lines

Position lines may be obtained from the following sources:

  • Visual: Visual position lines are bearings of the aircraft, to or from an object. They may be expressed as true bearings or relative bearings, depending upon the datum used.
  • ADF Position Lines: ADF position lines are obtained using automatic direction finding equipment in conjunction with NDB beacons on the ground. An ADF position line is the GREAT CIRCLE bearing FROM the aircraft to the transmitter. It may be measured:
    • Relative to the aircraft in which case it is a RELATIVE BEARING (RBI)
    • It may be measured from magnetic north in which case it is a MAGNETIC bearing (RMI)

Plotting complications are introduced because the bearing is measured at the aircraft and plotted from the station. When plotting, the bearing must first be converted to a true bearing by the application of true heading to a relative bearing or by the application of local variation at the aircraft’s DR position to a magnetic bearing.

The procedure which follows then depends upon the type of chart:

  • Mercator: The true great circle bearing must be converted to a rhumb line bearing before taking the reciprocal to plot from the station.
  • Lambert: The bearing to the station must be converted to a bearing from the station by the application of convergency.
  • Transfer of the aircraft meridian to the beacon meridian can apply the convergency.
  • For most plots a Lambert’s Chart will be provided.

Navigational Plotting

Fig17: D1 = 40, D2 = 20, p = 10, q = 8.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Fig23: D1 = 20, D2 = 30, p = 10, q = 3.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Fig16: D1 = 30, D2 = 20, p = 8, q = 12.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Fig18: D1 = 20, D2 = 30, p = 5, q = 4.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Fig21: D1 = 40, D2 = 20, p = 3, q = 6.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Fig22: D1 = 40, D2 = 30, p = 13, q = 6.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Fig19: D1 = 40, D2 = 30, p = 3, q = 6.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Fig20: D1 = 40, D2 = 20, p = 10, q = 6.
After leaving “ A “ find the heading alteration required at “ B ” to arrive at “ X “.

Townsville WAC Plotting

The locations featured are on the Townsville WAC (Also available in the exam work booklet). Find the list of information for all fights. Assume the aircrafts ground speed remains constant during the whole flight.

  1. You depart Townsville Airport at 0130UTC for a direct flight to Cardwell Township approximately (S18° 22' E146° 1'). You have maintained a constant HDG of 320° M and a TAS of 100kt. After following the coast you find yourself over Upper Stone Township at 0156UTC. You then change your heading for Cardwell.
  2. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA

  3. You depart Spring Creek Airport approximately (S18° 38' E144° 32') at 2300UTC for a direct flight to Ingham Airport. You have maintained a constant HDG of 080 degrees M and a TAS of 120kt. Due to bad weather you find yourself over Lucky Downs homestead at 2317UTC. You then change your heading for Ingham.
  4. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA

  5. You depart Lake Lucy homestead approximately (S18° 35' E145° 15') at 0314UTC for a direct flight to Camel Creek homestead (S18° 50' E145° 28') to refuel. At 0358UTC you depart Camel Creek for a direct flight to Townsville Airport while maintaining a constant HDG of 108 degrees M and a TAS of 110kt. Due to some cockpit distractions you find yourself over Rollingstone Township about to head out to sea at 0422UTC. You then change your heading for Townsville Airport.
  6. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA

  7. You depart Donnington Airpark approximately 20 nm south from Townsville at 0000UTC for a direct flight to Wando Vate homestead (S19° 40' E144° 51'). You have maintained a constant HDG of 255 degrees M and a TAS of 80kt. Due to a cross wind you find yourself over Battery homestead at 0055UTC. You then change your heading for Wando Vate.
  8. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA

Bourke WAC Plotting

The locations featured are on the Bourke WAC (Also available in the exam work booklet). Find the list of information for all fights. Assume the aircrafts ground speed remains constant during the whole flight.

  1. You depart ST George Airport at 0145UTC for a direct flight to Lightning Ridge Airport. You have maintained a constant HDG of 181 degrees M and a TAS of 100kt. After following Ballonne River you find yourself over Dirranbandi township at 0203UTC. You then change your heading for Lightning Ridge.
  2. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA

  3. You depart Narrabri Airport at 2350UTC for a direct flight to Mungindi Airport. You have maintained a constant HDG of 320° M and a TAS of 120kt. Due to bad weather you find yourself following the Newell Highway for Moree Airport with an ETA of 0017UTC. You then change your heading for Mungindi.
  4. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA

  5. You depart Wee Waa Airport approximately 22 nm west from Narrabri at 0105UTC for a direct flight to ST George Airport. You have maintained a constant HDG of 330° M and a TAS of 80kt. Due to a cross wind you find yourself over Mungindi township at 0140UTC. You then adjust your heading for ST George.
  6. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA

  7. You depart Narrabri Airport at 0426UTC for a direct flight to Wee Waa Airport to refuel. At 0538UTC you depart Wee Waa Airport for a direct flight to Walgett Airport while maintaining a constant HDG of 265° M and a GS of 102kt. Due to some in-flight distractions you find yourself over Whitewoods homestead (S29° 59' E148° 44'). You then change your heading for Walgett Airport.
  8. Find:

    • FPT M
    • TMG M
    • G/S
    • Drift (for first leg)
    • TE
    • CA
    • Alteration HDG
    • New HDG
    • ETI
    • ETA



WAC Answers