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CONDITION OF
RADIO
RADIUS OF RADIATION PATTERN
ON 121.5 MHz AT 10,000FT AGL CAN
VARY FROM 30 NM
OVER DRY SAND TO 90 NM OVER SEA
SH
SF
2.3.1 Electronic searching is used to search for survivors who may have activated a VHF (or
VHF/UHF) locator transmitter. An aircraft equipped with a VHF receiver may locate a
survival transmitter using procedures which are based on the assumption that an
undistorted radiation pattern is approximately circular. A searchmeter may be used to
assist a search operation and is basically a signal strength meter which can be plugged
into an aircraft VHF receiver.
2.3.2 The following procedures should be used during initial aural search without a searchmeter:
a. Set the aircraft receiver to its most sensitive condition-squelch disabled;
b. Note and report the position at which the signal is first heard (SH) and fades (SF)
and do not change altitude or the condition of the radio;
c. After the signal has faded select a heading estimated to take the aircraft through the
radiation pattern, but ignore any beacon signals received during the turn; and
d. Continue chording the radiation pattern until it is possible to establish a cocked hat
for the probable position of the beacon, (See Diagram 8).
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EMERGENCY PROCEDURES 24-Nov-2005 EMERG - 11
2.4 Carry out a final homing (See DIAGRAM 9).
ELT
121.5 MHz
SIGNAL BECOMING
WEAKER ON 121.45
MHz
121.45 MHz
POINTS OF
MAXIMUM
SIGNAL
121.4
MHz
DIAGRAM 9 - FINAL HOMING
2.4.1 The final homing procedures without a searchmeter are:
a. Track towards the estimated centre of the radiation pattern.
b. Set the aircraft receiver to its most sensitive condition and descend, if possible, to
be between l000 and 2000 feet above ground level in the estimated centre.
When the signal from the beacon is very strong and very clear, check on the adjacent frequencies
of 121.45 or 121.55 MHz;
c. Traverse the area bounded by the cocked hat, listening for the beacon on the adjacent
frequency;
d. On hearing the signal on the adjacent frequency, select and fly a heading which
results in a stronger signal. As the signal increases in strength, check further off
frequency and descend as required.
At this stage it is most important that each track should be a straight line. Helicopter
pilots should avoid any tendency to orbit a suspected site;
The accuracy of the homing will usually depend upon how far off frequency the signal
can be heard. Observers will find that a signal being received on, for example, 121.3
or 121.7 MHz (over land) will rise to a sharp peak only as the search aircraft passes
over the beacon site at 500FT above ground level. Where the terrain is heavily
timbered (eg. rain forest,), helicopter pilots should descend to lower levels and tune
further off frequency to achieve greater accuracy. Information gained during straight
and level flight only is most important and is the only data that should be used.
Where the signal is irregular, it is usually because the beacon is located amongst
obstacles such as trees, rocks, wreckage, etc. The resultant radiation pattern is no
longer circular and the signal heard/signal fade principles no longer apply.
2.4.2 The following procedures should be used during aural search with a searchmeter:
a. Set the aircraft receiver to its most sensitive condition-squelch disabled.
b. Plug the searchmeter into the SAR outlet.
c. Fly as high as practicable for aircraft type and weather conditions.
d. On receiving the emergency signal, advise the Rescue Co-ordination Centre (RCC)
of position, heading and indicated airspeed.
e. The radiation pattern from a beacon can either be approximately circular (regular)
or lobular (distorted). Where the signal received from the beacon is constant the
following procedures should be used:
(i) Fly a heading which will result in an increase in the reading on the search meter.
Maintain this heading at a constant altitude and airspeed (See DIAGRAM 10).
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EMERGENCY PROCEDURES 24-Nov-2005 EMERG - 12
= POINTS OF
EQUAL STRENGTH
RADIO SIGNAL HORIZON
RETURN TO
MIDPOINT
ELT
READINGS DECREASE
RETURN TO MIDPOINT
DIAGRAM 10 - SEARCHMETER PROCEDURES
(ii) Note the time and aircraft position at each half division on the searchmeter.
(iii) Continue (i) until readings on the searchmeter decrease. Select two positions
of equal reading and return to the midposition.
(iv) On arriving at the midposition turn 90DEG and note the readings on the search
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