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Aural Null Procedures Air Search. Module 9 of CASARA ELT Training Plan. Aural Null. Using aircraft communications radio. Aural Null. Procedure A. Procedure B. AURAL NULL PROCEDURE. In the event that your homer is not working, you must know Aural Null methods, “A”, and “B”.

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aural null procedures air search

Aural Null ProceduresAir Search

Module 9


CASARA ELT Training Plan

aural null

Aural Null

Using aircraft communications radio

aural null1
Aural Null

Procedure A

Procedure B

aural null procedure
  • In the event that your homer is not working, you must know Aural Null methods, “A”, and “B”.
  • The only equipment you need is:
      • VHF receiver
      • clock
      • map
      • pen
signal reception
Signal Reception

Beware of a difference of signal reception on the nose of the search aircraft, as compared to the signal off of the tail. Signal strength may vary enough between the two so as to make the results inaccurate. If this occurs it is recommended that readings be taken off of the nose. It will mean flying out of the signal, then making a 180 degree turn and coming back on the same track. When flying back towards the signal, take your readings once the signal is heard again.

Signal Faded

Signal Detected

when signal detected
When signal detected:
  • Descend to minimum reception altitude.
  • Disable squelch if possible and adjust radio volume to minimum reception.
when signal detected aural null procedure a
When signal detected:AURAL NULL PROCEDURE “A”
  • Fly a constant heading and draw a track made good on the map.
  • Pinpoint your position on map.
  • Once signal is lost, do a 180ºturn and mark the spot (A) where the signal is acquired again.
  • Maintain constant altitude and volume setting at all times.
when signal fades out
When signal fades out
  • Fly along the same track and pinpoint position of fade out (B), do another 180º.
  • Calculate mid-point of track made good (C).
  • From this mid-point plot at 90 degrees, a new desired track which extends on both sides of track made good.
  • Return to mid point and fly either direction to make good, the new track.
when signal fades out1
When signal fades out
  • When signal strength fades out, plot this point on your map (D)
    • Reverse course, signal will build and then fade. Plot point at which signal fades (E)
elt location
ELT Location
  • In theory, the ELT should be located at the mid point of the second track
  • Terrain, obstructions and aircraft wreckage can skew the points and make finding the ELT more difficult.

Fly to Calculated Halfway pt. turn left or right and fly until signal fade

Fly track until signal fade


Make 180 deg turn

Signal faded

Signal Detected

Mark Position


Make 180 deg turn

Signal Faded

Signal Detected

Mark Position

Calculated ELT Location

Calculate Halfway pt.

Mark Calculated Halfway pt.

Draw Track line

Draw Track line 90 deg to 1st track line


Signal Detected

Signal faded

Make 180 deg turn

Signal Detected

Mark Position


Mark Position

And heading

Fly to Calculated Halfway pt.


aural null procedure b
  • This method has both an advantage, and disadvantage:
    • ADVANTAGE: It is faster than Procedure “A”
    • DISADVANTAGE: It requires sufficient cockpit space to adequately plot the information
  • Requires:
    • VHF receiver - pen - dividers
    • map - ruler - 900 triangle
aural null procedure b1
  • Position of the aircraft is plotted as soon as the signal is heard
  • Continue on same heading for a short distance
  • Turn 900 either left or right, and proceed until the signal fades. Note this position
  • Turn aircraft 1800 and again plot where the signal is heard, and where it fades
aural null procedure b2
  • Approximate position of ELT is plotted by:
    • drawing chord lines between each set of “signal heard” and “signal fades” positions
    • Drawing perpendicular bisectors of each chord
  • Aircraft proceeds to the point where the perpendicular bisectors intersect.
  • The ELT should be there
that s all for now
That’s All For Now

Have a pleasant flight!