Mission Aircrew Course
Chapter 10: Electronic
Search Patterns
(Mar 2007)
Aircrew Tasks
O-2005 OPERATE THE AIRCRAFT DIRECTION FINDER
(P)
 O-2006 PERFORM ELT SEARCHES (P)
 O-2007 LOCATE AND SILENCE AN ELT ON THE
GROUND (P)
 O-2101 DESCRIBE HOW ELTS ARE DETECTED (P)
 O-2108 ASSIST IN ELT SEARCHES (O)

Objectives
Discuss the various types of ELTs. {O; 10.1.1}
 Describe how an ELT can be detected. {O; 10.2}
 Describe how the aircraft DF works in both the
Alarm and DF modes. {O; 10.3.1}
 Discuss using the DF during a typical ELT search
{O; 10.3.2}

• Response during initial phase, including signal fade
• Response when getting close
• Response as you pass over the beacon
Objectives

Describe the following ELT search methods:
{O; 10.4 – 10.7}
•
•
•
•
Homing
Wing null
Aural
Signal
Discuss signal reflection and interference.
{O; 10.9}
 Describe how to silence an ELT and the legal
issues involved. {O; 10.10}

Emergency Locator Transmitter
Direction Finding for Aircrews:
use of equipment commonly
found in CAP aircraft
©2000 Scott E. Lanis
5
Objective: The Elusive ELT

Automatic radio beacon (100 milliwatts)
• Roughly equal to that of a regular flashlight
 Can
be heard on a line-of-sight basis.
 Remember that the ELT may be attached
to an aircraft or vessel in distress!
Click Icon to
Hear an ELT
©2000 Scott E. Lanis
6
The ELT

Activated by g-force (when armed)
• Some can be activated by the pilot in the cockpit

Three frequencies:
• 121.5 MHz (VHF emergency)
• 243 MHz (UHF emergency – military guard)
• 406.025 MHz (third generation advanced ELT/EPIRB/PLB)

General types:
•
•
•
•
•
•
General aviation aircraft
Military (“beepers” or “beacons”)
Marine EPIRB
Test station (training practice beacon)
Personal Locator Beacons (PLBs)
Advanced (406)
ELT Antenna
Most aircraft have ELTs installed
But they
don’t
always
survive a
crash
Most aircraft have ELTs installed
But they
don’t
always
survive a
crash
Military beacons
Most common type is the URT-33/C
 Personnel ejecting/parachuting will have a 243
MHz beacon
 Some downed pilots may be able to
communicate via two-way radio on 243 MHz
using a PRC-90 military survival radio

• Beacon mode transmits like an ELT on 243 MHz
• You can monitor this frequency on your aircraft DF
Personal beacons

Personal Locator Beacon (PLB) or
Personal Emergency Transmitter
(PET):
• Intended for hikers and other remote
wilderness travelers
• MOST Use a 406 MHz transmitter and a
121.5 MHz homing signal (at only 25
milliwatts)
• Many are also equipped with a built-in
GPS receiver that provides lat/long
coordinates
• Each PLB must be registered
• See discussion of Advanced ELTs
Marine EPIRB
Emergency Position Indicating Radio Beacon
 Similar to an ELT, an EPIRB is used on ships and
boats
 Mandatory on certain commercial vessels
 Some activate automatically and others are
manually activated
 Many are now 406 capable

Advanced ELTs

Designed to operate with SARSAT/COSPAS
• 406.025 MHz beacons have data burst encoding that identifies
each (registered) individual beacon
• Also produces a 121.5 MHz homing signal and may transmit
GPS coordinates
• Sends a coded signal that can be used to obtain the owner's
name, address and type of aircraft, so AFRCC can call the
number to see if the aircraft is really missing (70% resolved)
• Since geostationary satellites process the signal it will be
heard more quickly and allow a much faster response (~ 6
hours). If the unit has a GPS receiver, it can transmit lat/long
coordinates to further speed the search. The signal can also
penetrate dense cover (e.g., trees).
• Still very expensive (~ three times as much as a 121.5 MHz ELT)
Practice Beacon

Training Practice Beacons
• Includes ones used by CAP
All should be converted from 121.6 to 121.775
MHz by now (if it isn’t, don’t use it, get it fixed)
 During practice searches, avoid calling the
practice beacon an ‘ELT’ when communicating
over the radio

• May cause confusion

Always use the term ‘Practice Beacon’
Testing an Aircraft ELT
Can test the aircraft’s ELT within the first five
minutes after each hour
 Only allowed up to three sweeps
 When was the last time you tested the ELT in your
aircraft?
 Do you regularly monitor 121.5 MHz after you
land?

• Ensure your ELT didn’t activate
• This isn’t considered a test, by the way, but you can try this
excuse if you like
Inadvertent Activation
Excessively hard landings (Welcome aboard, Ensign!)
 Inadvertent change of switch position
 During removal/installation
 Malfunction
 Non-ELT source on 121.5 MHz (computers, broadcast
stations, even pizza ovens!)
 Monsieur Murphy

False Alarms

At least 97%+ of received ELT signals are false
alarms
• For 121.5 MHz ELTs abut 1 in 1000 are actual emergencies
(2 in 100 composite alerts)
• For 406 MHz ELTs abut 1 in 10 are actual emergencies

What’s the big deal?
• SARSAT can only monitor 10 ELTs at once
• Easy to overload the system
• They block emergency communications on 121.5 and 243
MHz (guarded by towers, ARTCC, and the military)
Detection Timeline
Accuracy of
SARSAT/COSPAS

For a regular 121.5 MHz beacon:
• Said to be a 12-16 nautical mile radius (~ 452 square nm)
• Actually an oval shape with a 50% probability of being 15 nm
wide and 7 nm high
• System is more accurate North to South (latitude)
• Average six-hour detection/alert
For a 406 MHz beacon it’s a 1-3 nm radius (~ 12.4
square nm) with 45 – 60 minute detection/alert
 For a 406 MHz beacon with GPS it’s a 0.05 nm
radius (within 100 yards) with an average fiveminute detection/alert

SARSAT Video
QUESTIONS?
OK, So How Should I Treat an
ELT Mission?
AS AN EMERGENCY!
 Its not possible to know whether an ELT signal is a
distress signal or a false alarm
 Although the statistics are against it, you must
act as though it is a distress call
 If you take advantage of it, every ELT mission
allows you to keep your skills sharp!

Locating the ELT Signal
Route or parallel track to pick up the signal
 If no SARSAT hits or definitive LKP:

• 4,000 to 10,000 AGL
• Large track spacing (start at 60 nm, then do halves)

Once signal is located, DF the signal
Direction Finder (DF)
• A direction finder compares signal strengths from
two antenna patterns to let the user know:
– When you are “centered” on a signal
•headed directly towards OR away from from
the signal source
– Which direction to turn when not centered
– Similar to an ADF needle, but only points left or
right, hence the term “left-right homing”
L-Tronics DF
Normal: Alarm toggle in ‘up’ position
 DF: toggle is ‘down’

DF Antenna
These are mounted on the bottom, but
may be on top
Step 1: Acquire the Signal
To hear the signal you can use your L-Tronics
receiver or one of your comm radios
 To acquire with a comm radio, turn the
squelch OFF (pull out the volume knob out or flip the

appropriate switch)
• The static you hear may be annoying, but it will allow
you to hear the signal at the earliest possible time
• Allows for a weak or distant signal to be heard
 Proceed
at a reasonable altitude to the
SARSAT composite hit, or to the point
designated by your incident commander
©2000 Scott E. Lanis
29
Beginning The Search: Altitude
Selection





Higher altitudes allow for reception of the ELT signal at greater
distances
ELTs transmit on 121.5 MHz and 243.0 MHz, both of which limit
reception to “line of sight”
Terrain will block ELT signals
HIGHER is therefore usually BETTER to acquire a signal
Medium altitude is generally better for searching (after signal
heard)
• 3,000 to 5,000 AGL
NO
SIGNAL
SIGNAL
HEARD!
ELT
©2000 Scott E. Lanis
NO
SIGNAL
30
Altitude Selection
ELT RECEPTION DISTANCE
35000
30000
25000
20000
15000
10000
5000
©2000 ScottNautical
E. Lanis
DISTANCE,
Miles
265
200
147
121
95
69
56
34
30
18
0
0
ALTITUDE, Feet AGL
40000
31
Step 2: Track (DF) the Signal

There are many different ways to DF an ELT
signal:
• Left-Right DF Homing (L-Tronics DF)
• Wing Shadow Method
• Aural Search
• Metered Search
• Combinations of the above techniques
©2000 Scott E. Lanis
32
Wing Shadowing

By flying the airplane in a circle, at some point the
wing will block the ELT signal to the receiver antenna
• This causes an audible decrease in volume, called a “null”
 Almost
any VHF-AM aircraft communications radio
may be used with this method
©2000 Scott E. Lanis
33
Wing Shadowing: Antennas
To properly use the Wing Shadowing method, you
MUST know where the antenna for the radio you
are using is installed & located on the aircraft
 Communications radio antennas are usually, but
not always, located above the wings

• Can be above the fuselage, in the tail, etc.

L-Tronics Aircraft DF antennas may be above or
below the aircraft
• Below the aircraft is the preferred installation
©2000 Scott E. Lanis
34
Communications Antennas
Above the Wing
Antennas Above
the Wing
©2000 Scott E. Lanis
35
DF Antennas Below the Wing
Antennas Below
the Wing
©2000 Scott E. Lanis
36
QUESTIONS?
How To DF by Wing Shadowing
(Also Called Wing-Null Method)
Fly a constant bank angle
360° turn
 the audio will “null,”
 or get significantly quieter,
 when your wing blocks the
antenna’s reception of the
ELT signal

N
W
E
S
©2000 Scott E. Lanis
38
Wing Shadowing:
Signal Blocking
For Antennas Above the Wings
NULL
NULL
NULL
SIGNAL
ELT
©2000 Scott E. Lanis
39
Wing Shadowing:
Antennas Above the Wing
Turn in a circle until you hear the null
(significant decrease in volume)
 The ELT is 90º to your LEFT
 SUBTRACT 90º from your
heading
 Or, keep it simple—use the
90º index

ELT
©2000 Scott E. Lanis
40
Wing Shadowing:
Signal Blocking
For Antennas Below the Wings
NULL
NULL
SIGNAL
NULL
ELT
©2000 Scott E. Lanis
41
Wing Shadowing:
Antennas Below the Wing
Turn in a circle until you hear the null
(significant decrease in volume)
 The ELT is 90º to your RIGHT: ADD 90º to your
heading

ELT
©2000 Scott E. Lanis
42
Aural (Hearing) Search
Method







This is based on the assumption that the area of equal beacon
signal strength is circular: do NOT adjust volume during this
search; you will need it to determine equal levels of signal
Begin by plotting your position as soon as you receive the ELT
signal
Fly that course for a short distance, then turn 90º left or right and
proceed until the signal fades
Turn around (180º) and mark where the signal fades on the other
side of the circle
Plot chord lines similar to that of the diagram
Bisect the chord lines at a perpendicular
Plot a course to the location where the perpendicular lines
intersect: this should be the location of the target!
©2000 Scott E. Lanis
43
Aural Search
Equal signal strength circle:
barely audible signal in aircra
receiver at search altitude
com
m
altitu ence lo
w
de p
atter
n
d
ELT
SIGNAL
FADES
esce
ndin
g
SIGNAL
HEARD
chord 2
SIGNAL
HEARD
cho
rd 1
rd
o
ch
3
SIGNAL
FADES
SIGNAL
HEARD
©2000 Scott E. Lanis
44
Metered Search
(Build & Fade) Method







This search requires a signal strength meter (like that
on the L-Tronics DF units-if the DF portion of the unit is
inoperative you can still use this type of search as
long as RECeive is OK.
Note your signal strength when beginning the search.
Fly a straight line until the signal gets lower, then
increases to your original level.
Turn 180º and return to the lowest level of signal, then
turn 90º left or right.
You should now be headed directly towards or away
from the transmitter.
If the signal increases in strength, you are headed
directly for the ELT.
If the signal decreases
inScott
strength,
©2000
E. Lanis turn 180º
45
Metered Search
3
ELT
2
MAXIMUM SIGNAL
6 THEN DROP
4
5
1 FIRST SIGNAL
©2000 Scott E. Lanis
46
Left-Right DF Homing
Most CAP corporate aircraft have L-Tronics
LA-Series Left-Right Homing DF units
 These units operate virtually the same, but
there are two major varieties:

• Single Meter Models
• Dual Meter Models
©2000 Scott E. Lanis
47
L-Tronics DF Types

Single Meter Model
 SENS
REC
243
ALARM
AUX
121.775
VOL
DF
121.6
VHF-DF
121.5
OFF
L-Tronics

Dual Meter Model
DF
ALARM
STRENGTH
 SENS
VOL
243
121.775
AUX
121.6
121.5
VHF
DF©2000 Scott E. Lanis
OFF
L-Tronics
48
Frequency Switch
Selects frequency to be used
 Use 121.5 MHz for actual ELTs/EPIRBs
 243.0 MHz may also be used for all actual electronic
searches
 Use 121.775 MHz for training
 Refer to owners manual for use of the “AUX” position

 SENS
REC
243
121.775
AUX
ALARM
VOL
DF
121.6
121.5
VHF-DF
©2000 Scott E. Lanis
OFF
49
L-Tronics
Mode Switch

Only Single-meter units have this switch
• Dual-meter units use two displays, so both REC and DF operate continuously and
simultaneously

REC is short for RECeive mode
• REC makes the unit’s dial work as a strength meter

DF is short for Direction Find
• DF gives left-right homing to the ELT/EPIRB signal

ALARM is for NON-MISSION flights only
• Use only during normal flying to alert the presence of an ELT or EPIRB
 SENS
REC
243
121.775
AUX
ALARM
VOL
DF
121.6
121.5
VHF-DF
©2000 Scott E. Lanis
OFF
50
L-Tronics
Volume & Sensitivity



Volume controls the audio level to the speaker or headsets
Sensitivity controls the amount of signal that enters into the DF unit
• It is critical that the proper amount of signal enters the DF: halfscale, or the middle, is an optimum starting place
As the signal gets stronger, reduce SENSITIVITY, not volume
• The DF will be unreliable when too much signal is received, so you must
cut out part of it by reducing the sensitivity
• More than three-quarters scale is too much
DF
ALARM
STRENGTH
 SENS
VOL
243
121.775
AUX
121.6
121.5
VHF©2000 Scott E. Lanis
DF
OFF
51
L-Tronics
DF SETTINGS FOR
SINGLE METER MODELS

MISSIONS
•
•
•
•
•

Select 121.5 (or 121.775 for training missions)
Select DF Mode
Turn Sensitivity to Maximum (Full Clockwise)
Turn Volume to About Mid-Scale (comfortable level)
DF Needle Will Move Slightly Left and Right
NON-MISSION FLIGHTS
•
•
•
•
Select 121.5
Select Alarm Mode
Turn Sensitivity To Maximum
Do not fly a mission in the alarm mode, it takes too long to
activate
©2000 Scott E. Lanis
52
DF SETTINGS FOR
DUAL METER MODELS

MISSIONS
• Select 121.5 (or 121.775 for training missions)
•
•
•
•
•

Ensure Alarm Toggle OFF
Turn Sensitivity to Maximum (Full Clockwise)
Turn Volume to About Mid-Scale (comfortable level)
DF Should Stay About Centered
Strength Meter Will Move Up-Scale to Right
NON-MISSION FLIGHTS
• Select 121.5
• Turn Alarm Toggle On
• Turn Sensitivity To Maximum
©2000 Scott E. Lanis
53
PRE-FLIGHT FUNCTIONAL
CHECK
Just as you pre-flight the rest of the aircraft,
you should preflight your DF when going on
an ELT electronic search mission
 These procedures are covered in the Mission
Aircrew Reference Text and are summarized
for premission reference in the Flight Guide.

©2000 Scott E. Lanis
54
SIX STEPS


Use these 6 steps for locating ELTs and EPIRBs with
L-Tronics LA- series airborne DF equipment
Use the full procedure every time for the best
results
•
•
•
•
•
•

RECeive
HALF
DF
TURN
CHECK
SHOOT
Each of these steps will be described in detail in
the slides to follow
©2000 Scott E. Lanis
55
Step 1: RECeive
Once you have started to receive the ELT or
EPIRB signal on the proper frequency
 If you have a single-meter unit, turn the
mode selector to RECeive and turn the
volume to a comfortable level
 If you have a dual meter unit, refer to the
STRENGTH window (no need to change
modes)

©2000 Scott E. Lanis
56
RECeive Mode/STRENGTH
Window

In receive mode or in the strength window, the unit measures
signal strength
• Needle to the left means low; to the right means high


Values are relative depending on the sensitivity you have
selected
You may still be able to use the strength meter even if the DF is
not functioning perfectly
• It is possible to locate an ELT using only the Receive Mode
• Utilize Aural Search/Metered Search methods to accomplish
• If the unit isn’t completely operable, try wing shadowing using one of the
aircraft’s communications radios and use the DF unit’s strength meter as a
backup using the aural/metered methods
Step 2: HALF

Now that the unit is in RECeive mode and you
have a good signal, turn the Sensitivity Knob
to HALF SCALE
• This is in the center of the window
 If
you are flying with a dual-meter unit, turn
the Sensitivity Knob so the needle reads HALF
SCALE in the STRENGTH window
 A half-scale strength reading will prevent too
much signal (over sense) from entering the
unit and will provide you with a good starting
point
 It is also the optimum for the DF homing
antennas
©2000 Scott E. Lanis
58
Step 3: DF
For single-meter units, turn the mode selector
knob to DF
 In DF mode, you can think of the needle as
always pointing Direct to Follow the target.
 For dual-meter models, simply refer to the DF
window (no need to change modes)

©2000 Scott E. Lanis
59
A Direction Finding Primer:
Antenna Theory


Antennas can be more or less directional
depending on their design
Imagine a car radio antenna: it is
unidirectional
• Its pattern looks like the one on the left

A Satellite Dish is highly directional
• It would have a pattern like the one on the right
car radio antenna
(monopole)
satellite dish (parabolic reflector)
DF Antenna

The aircraft DF unit has a 2 or 3 “element” antenna
• Commonly, we might call this two or three antennas
• It just means there are two or three rods!

This antenna setup is directional
• One element actually receives the signal
• The other elements (rods) reflect the signal away from the
first rod
Antennas Below
Antenna
the WingElements
Antenna Reception Pattern

When viewed from the bottom, an antenna
setup like the one pictured on the previous
slide produces a reception pattern like the
one shown here
• This pattern is called “carotid,”
which means
“heart-shaped”

The pattern is the same
even if the antennas are
mounted above the
wing
Element 1
©2000 Scott E. Lanis
2
3
62
DF Unit Antenna Pattern
REFLECTOR
ELEMENTS
TOP VIEW
DIRECTIONAL
ANTENNA
PATTERN
RECEIVING
ELEMENT
AIRCRAFT VIEW
Direction Finding
Mode/Window

The DF mode rapidly alternates the receiving
and reflecting antenna elements
• It chooses one element as the receiver and the
other two as the reflectors, then switches to the
other set

This produces a carotid pattern each time
the unit switches
• one is shown in blue, the other in yellow



By comparing the two patterns, the unit
will determine when they are equal
When they’re equal, the needle centers!
When the needle is centered,
the target is either directly ahead or
behind you!
Step 4: TURN
Turn at least one FULL circle, noting where the
DF needle centers
 Under good conditions, the needle will
center twice

• When facing directly at the source of the signal
• When facing 180º away from the target

You will solve this problem (called
ambiguity) in the next step
©2000 Scott E. Lanis
65
DF CENTERS
ELT (Possibility 1)
Alternating
Antenna
Patterns
WHEN THE
PATTERNS
ARE EQUAL,
THE DF NEEDLE
CENTERS!
Alternating
Antenna
Patterns
ELT (Possibility 2)
Step 5: CHECK
Use a Turn to Tell
 Remembering that in DF mode the needle
always points Direct to Follow the target
 When you have the needle centered, turn left
or right

• If you turn left and the needle goes left, the ELT is 180º
from your present heading
• If you turn left and the needle turns right, the ELT is dead
ahead
©2000 Scott E. Lanis
67
AMBIGUITY

When Needle
Centers
• ELT is Directly
Ahead or Behind
This situation is
called “ambiguity”
 To Solve
ambiguity:
 Use Turn to Tell

• Make a turn left or
right
• The needle always
pointsDirect to Follow
the Target (DF!)
ELT (Possibility 2)
ELT (Possibility 1)
DF NEEDLE




Compare the RED (LEFT)
and the BLACK (RIGHT)
antenna patterns
In this case, the
LEFT pattern is
stronger than
the RIGHT
In DF mode, the
needle would then
point LEFT
The needle always points
Direct to Follow the Target!
ELT
ELT (Possibility 1)


Actual ELT position
is unknown to user
Make a small turn
left or right
• As a teaching
reminder, “Use a
TURN to TELL”
SOLVING
AMBIGUITY
ELT (Possibility 2)
ELT (Possibility 1)


Actual ELT position
is unknown to user
Make a small turn
left or right
• As a teaching
reminder, “Use a
TURN to TELL”

Example:
• TURN LEFT
• needle goes left
SOLVING
AMBIGUITY
ELT (Possibility 2)


Actual ELT position
is unknown to user
Make a small turn
left or right
• As a teaching
reminder, “Use a
TURN to TELL”

Example:
• TURN LEFT
• If needle goes left
• ELT is to your left
(behind you)
ELT (Possibility 2)
SOLVING
AMBIGUITY
ELT (Possibility 1)


If you turn Left and the
needle moves Right
The ELT is in
Front of you!
SOLVING
AMBIGUITY
ELT (Possibility 2)
ELT (Possibility 1)



If you turn Left and the
needle moves Right
The ELT is in
Front of you!
Example:
• Turn left
• Needle goes
right
SOLVING
AMBIGUITY
ELT (Possibility 2)
ELT (Possibility 1)

Solution:
• If you turn Left
and the needle
moves Right
• The ELT is in
Front of you!
SOLVING
AMBIGUITY
Step 6: SHOOT
Use your DG to determine a
bearing to the target & follow it
 You may need to fly through a
zone of signal dropout
 Be watchful for signs of signal passage

• If you get signal passage, consider using the “pinpointing the
target” techniques listed in this presentation
 Frequently
repeat the FULL SIX STEPS to ensure you
are heading in the right direction and that you
didn’t inadvertently over fly the ELT
©2000 Scott E. Lanis
76
How A L-Tronics DF Unit Works:
Summary

Two Main Modes of Operation
• RECeive
• DF
 RECeive Mode is a Strength
• Left is low, right is high

Meter
DF Mode Centers on Signal
• Always points to the signal
• Use a Turn to Tell when solving ambiguity

Aircraft and ground units work the same way
QUESTIONS?
Reflections
Reflections of an ELT signal work just like a
flashlight off of a mirror
 Any flat, hard, or wet object can cause
signal reflections

•
•
•
•
•

Mountains, especially cliff faces
Hangars and other metal structures
Wet grass or ground
Snow
Large bodies of water or ice
Power lines can also have a large effect on a
low-powered signal such as an ELT
©2000 Scott E. Lanis
79
Beating Reflections

Check your sensitivity at half-scale or lower
• But ensure that its high enough to receive adequate signal



Reflections will generally be weaker than the most direct path to
the target
Following reflections will generally take your closer to the target
If sensitivity is set to minimum, try DFing on a different frequency
• For example, if you are trying to locate an actual ELT on 121.5 MHz, try
locating it on 121.6 or 121.775 MHz when you get close

When all else fails, fly somewhere else to get a good DF bearingor try that at the first sign of problems!
©2000 Scott E. Lanis
80
Carrier-Only Signals
• You don’t always need to hear the ELT or EPIRB to find it
– A carrier-only signal may be broadcasting with no audible sweep
• This is especially true with low or old batteries, damaged ELTs, or
spurious transmissions
• You can identify a carrier-only signal by DEFLECTION
• If it looks like you’re finding an ELT, even if you can’t hear it, you have
good DEFLECTION
• Good needle deflection generally indicates a signal that is strong
enough to DF
• Compare your deflection to another frequency
– If you are using 121.5 MHz, try it on 121.775 MHz
• If deflection is the same in both frequencies, you DON’T have a
signal, just random noise (or your DF unit may be broken)
• If deflection is different, keep at it! You have a signal.
• If a signal is only received on 243 MHz, it may be a malfunctioning
antenna (e.g., an FAA tower). If you DF to the location (particularly
on or near an airport) and you keep ending up at an antenna,
investigate. Find out who owns the antenna and its purpose. Inform
©2000
Scott E. troubleshoot
Lanis
81
the IC and let the controlling
agency
the problem.
Vertical Reflections &
Signal Dropout





The transmission pattern (similar to the reception
pattern of the DF antennas, only for transmission) of an
ELT is not a perfect circle or sphere (especially in the
profile view)
It has lobes, or, stronger and weaker points
This is accentuated when the ELT is transmitting from a
location above the surrounding ground
When you get a good DF heading and the signal
fades or drops out completely you may just be outside
of one of the signal lobes
When you reacquire the signal, it should be stronger
than when you lost it (if its not, you’re probably going
in the wrong direction!)
©2000 Scott E. Lanis
82
Signal Dropout


If you encounter a signal dropout, continue to fly on your last good
DF heading
You should reacquire the signal in a few minutes
• Actual time will depend upon your distance to the target

If you are unable to reacquire, return to where you last heard the
signal and re-DF
NO SIGNAL
SIGNAL
HEARD
©2000 Scott E. Lanis
83
Signal Strength


The rate of change in signal strength increases as you get closer to
the transmitter, and RECeive mode or the STRENGTH window
measures signal strength
This is due to Maxwell’s inverse square law:
• When you double the distance from an object, the energy it you receive from
it is 1/4 of what you originally received, or the inverse square: 1/(22) = 1/4
– After Scottish Physicist James Clerk Maxwell, 1831-1879


This is an inverse exponential relationship
You will therefore need to turn down the sensitivity to keep the unit at
half scale in the RECeive mode or STRENGTH window much more
often as you get close to the source of the signal
• This should let you know that you’re getting close
©2000 Scott E. Lanis
84
Signal Strength Rate of
Change
©2000 Scott E. Lanis
85
Cone of Confusion
Cone of
Confusion
Antennas receive best when the
“pole” is perpendicular to the signal (a 30 dB
loss for cross-polarized)
 When you approach the directly
overhead position on an ELT, your
DF will become unreliable

• It may swing left and right
• It may center regardless of your heading

You should practice to see what this
“station passage” reading looks like
• It is similar to crossing a VOR
©2000 Scott E. Lanis
86
Reception in the
“Cone of Silence”


You may also get a significant drop in ELT signal since the antennas
receive poorly directly off of their tips (a 90 dB loss)
Although called a cone of silence, you will probably only see & hear a
large decrease in signal instead of complete silence
POOR
antenna
GOOD
©2000 Scott E. Lanis
87
Pinpointing the ELT



If you get a station passage indication, make an approximate
180 degree turn and DF back to the target
Repeat this process using different approach angles
each time, remembering that
your path may be curved due
to wind (like uncorrected
NDB holding)
The point where station
passage is received
several times
should be the
location of
the target
2
3
1
©2000 Scott E. Lanis
88
Pinpointing the ELT

After you think you have the target located
• make a low pass over the suspected location and
visually scan
• if signal strength decreases significantly or drops out,
climb back and try again
• this is not the target: sometimes false targets will appear
due to reflections or other interference

If you hear the ELT at low altitude, you
probably have the right place
• a low pass down a runway might be a good idea if you
suspect a particular airport
©2000 Scott E. Lanis
89
QUESTIONS?
Becker SAR-DF 517

Completely different theory of
operation from L-Tronics DF
• Pseudo Doppler Shift
• Beyond the scope of this course
• The advanced ELT course has an
explanation




Easy to use
Displays a delayed average heading
to the beacon
Can be used on 121.5, 243.0, or
406.025 MHz
Able to process newest ELTs, EPIRBs, &
PLBs
Becker Operation
Power
Mode
Page
Tune
Squelch
DF
Locate
Power



POWER Press the
ON/OFF button—unit
should power up and
illuminate
Be prepared to execute
the next steps…
If you’re not fast
enough, you may need
to recycle power (turn it
off and back on)
Mode








MODE Using the PAGE knob (upper
right knob), select:
EMERGENCY for an actual SAR or
TRAINING for a training mission
This setting can only be changed on
power up
Recycle power to change the Mode
After setting EMERGENCY or TRAINING,
just WAIT until the unit automatically
goes to the next page
The “wait time” is about 15 seconds
Don’t push any buttons or turn any
knobs during this period
Page




Use the PAGE knob to cycle to desired page
Page 1 is most like an ADF
Page 2 is good for forward quarter only
Page 3 is most easily read by the entire crew, but only
in relative bearing
Tune







The lower-right +/- knob changes the
frequency
You want 121,500 for an actual SAR or
121,775 for training
You can alternately use 243,000 or
243,550 respectively
You will only be able to select training
frequencies while in the training mode
Similarly, you can only select actual SAR
frequencies in the emergency mode
156,800 is for Marine Band Channel 16
EPIRBs
Notice the commas: the Becker is made
in Europe; the commas replace a
decimal point
Squelch

Squelch Knob




Squelch Setting Triangle 
Ambient Noise Level

Adjust the squelch knob on the
upper left of the unit
The squelch knob may be marked
SQL or DIM (depending when your
Becker was made)
Adjust the small triangle arrow until
it is pointing barely above the solid
bar
The solid bar represents static or
ambient noise, but you will want to
listen and make sure that the
“static” is not actually a signal
When trying to acquire a signal,
you may want the squelch all the
way down
You may also want to do this to
make sure you can hear audio
from the Becker
Turn the lower left knob to adjust
the volume to a comfortable
listening level
DF (Direction Find)











Follow the relative bearings to the ELT
Use homing procedures like an ADF
Correct for strong winds, if known
Remember that these are RELATIVE bearings with
the nose of the aircraft being 360°/ 000° !!!
If you are showing a >006> that means turn right 6°
If the unit shows <354<, then turn LEFT 6°
This is similar to a fixed-card ADF
“Rub The Tub” RB + TH = TB
Relative Bearing + True Heading = True Bearing
This is also true if we replace magnetic bearing
and heading instead of the trues: RB + MH = MB
Therefore if the Becker DF indicates >010> and you
are flying a 270° heading, the magnetic bearing of
the ELT is 280°. Add right, subtract left.
Becker Direction Finding Notes
The clear marbles indicate when the
Becker first and last receives the ELT
signal in its circle
 Watching the clear marbles will give
you an indication of how coherent your
DF solution is

DARK MARBLE
• The marbles will always jump around; if they jump
around a LOT you don’t have a good DF
• You can test this by seeing what your indications
are when you reduce the squelch enough to “DF”
static
• The clear marbles will jump all over the place
• Static can sometimes look like a carrier-only
signal
>020>
CLEAR MARBLES

The dark marble should be fairly stable
on an actual signal because of signalaveraging software
Locate
After flying over the ELT, you should get a
“station passage” indication
 Turn around and re-DF to locate the target
 This is similar to locating with the L-Tronics DF
 If you keep the signal at 090 or 270, you can
fly a “turn around a point” using the DF
 If the target isn’t visually significant, this will
give your Scanner(s) the opportunity to put
eyes on the target

Bearing on More than One
Transmitter






If bearing from a long
distance, the DF will be
pointing at the middle of the
two transmitters
This is because the Becker
averages the signals it gets
Exactly in the middle
between two transmitters, the
DF will display an unusable
bearing value
The clear marbles will swing
WIDE (180 degrees or more)
when in the middle of 2
averaged signals
Exactly over one transmitter
the DF will be pointing to
another (garbling cone)
Tactic for this situation: don’t
fly the approach exactly
following the indicated
averaged bearing: fly about
20 degrees left or right
Becker Thoughts







The Becker unit is not as sensitive as the L-Tronics DF, so you must be
significantly closer to the ELT to get initial signal
Because it uses averaging functions, it will not instantaneously point to an
ELT like the L-Tronics unit—there is defnitely a delayed raction
The displays on the Becker lead you to believe that it is a pseudo-RMI or
ADF type pointer. This is not the case. Even when the complete circle
(page 1) is displayed, the arrow only indicates left or right, NOT how
much (such as an ADF). The same is true for the “pie” display, page 2
Look to the “dark marble” to indicate the relative direction of the signal;
this acts as an ADF-type pointer
If you do not have an operable training beacon to practice with, pick an
AWOS, ASOS, or other continuously-transmitting source that is within the
training frequency range. If you tune it in (see the manual, training
mode only) you can DF it. A caution with this method, however, is that
an AWOS transmits at least 250 times the power level of an ELT. This
makes DFing an AWOS much easier than an ELT
Be careful with the unit as it costs roughly $10,000. MAKE SURE THE UNIT IS
OFF DURING ENGINE START/SHUTDOWN. Some installations have the DF
independent of the avionics master and the unit is sensitive to surges
from start/shutdown.
The complete user manual is available at http://www.beckerusa.com
After Locating The ELT
After location, coordinate with ground teams
to bring them on-scene
 Use radio communication and relay GPS
coordinates
 Pick up the ground team at a predetermined
location and lead them to the target
 Alternately, coordinate a new pick up point
on the radio
 Practice your air-to-ground coordination
skills often

• try it both with and without radio communication

©2000 Scott
E. Lanisunique ES skill!
Air-to-ground is CAP’s
best
103
DF upon Landing
Many times the ELT is located at an airfield where
it is easier for you to land and locate the ELT than
it is to get a ground team to the scene
 You can use a hand-held radio or hand-held DF
unit
 The most commonly used handheld DF in CAP is
the Little L-Per
 You did remember to put one of these (with fresh
batteries) in the aircraft before you left, didn’t
you?

Little L-Per
 Six
Steps
• Receive
• Half
• DF
• Center
• Turn
• Shoot
OK, which of these planes is it in?








Use Little L-Per or…
Use Body Shielding
With any hand held aviation band radio, you can locate
an ELT
A Jetstream radio also works great
Same concept as wing null method, you are just using your
body to block the signal to the antenna
When you get very close, there will be too much signal to
get a null
Use Frequency Offset Method—try 121.6 instead of 121.5
As you home in, tune in 121.6—you can tune further away
the closer you get
How To Body Shield: The
Null
SIGNAL

NULL!
No Signal To Your Receiver
• The Sound Gets Softer!
• The ELT Is Directly To Your Back
• Throw your thumb over your shoulder to
point to the ELT
ELT
Airmobile UDF Team 101







Once you’ve narrowed the suspects down to one or two
aircraft (usually side-by-side), remove the radio’s antenna
and hold it next to one of the ELT antennas
Turn the volume down until you just hear the signal
Don’t key the radio’s transmitter with the antenna removed
Move to the other aircraft’s ELT antenna
If the signal is stronger you probably have it; if weaker, its
probably the other aircraft
May also put an aluminum foil ‘sleeve’ over the antenna
Can also combine this with the frequency-offset method
OK, where is the thing?
(IN the aircraft!)






ELTs are usually located in or near the rear of the aircraft.
Also look for remote switches.
Single-engine Cessna: right side of the upper baggage
area immediately aft of the baggage door
Multi-engine Cessna: left side of the fuselage just forward
of the horizontal stabilizer. Accessed through a small pushplate on the side of the fuselage.
Single- and multi-engine Piper: in the aft fuselage.
Accessed through a small access plate on the right side of
the fuselage.
Single- and multi-engine Bonanza: in the aft fuselage.
Accessed through a small access plate on the right side of
the fuselage.
Large piston twins (e.g., King Air) and small jets: if installed
its probably in the rear section. No visible antenna. May
have a small round push-plate that lets you manipulate the
ELT switch.
Silencing the ELT


The preferred method is to have the owner (or
someone designated by the owner) turn it off and
disconnect the battery
Second best is to just turn it off
• The owner may put the switch to ‘Off’
• This may not always work since a malfunctioning switch could
be the problem
• If this is done, listen to 121.5 to ensure the beacon has been
deactivated and that it doesn’t go off again
• Remind the owner he will need a new battery if the ELT has been
transmitting for more than an hour

A “foil tent” is seldom used–it is temporary and last
resort
Silencing the ELT


Ensure that the owner is notified that the ELT was disabled
If you can’t get a phone number, you can place a note on
the aircraft (not the window)
WARNING! 
to prevent interference with a bona fide
emergency and with the Search and
Rescue Satellite System,
YOUR ELT/EPIRB HAS
BEEN DEACTIVATED!
by: C.A.P Search & Rescue Team
For Further Information, Contact: name, phone #
Legal Issues





Per CAP regulations and trespassing laws, CAP members will not
enter private property and should not do anything that could
cause harm or damage to the distress beacon or aircraft/vessel
CAP members do not have the authority to trespass onto private
property, either to gain access to the aircraft or to enter the
aircraft to gain access to the ELT
Entry to the ELT should be made by the owner or operator or law
enforcement
A transmitting ELT is under the legal authority of the FCC, and
federal law requires that it be deactivated ASAP (a crashed
aircraft is under the authority of the NTSB)
Besides the owner/operator, some owners give FBO personnel
permission to enter their aircraft
Legal Issues




While entry upon private property may be justified if such
an act is for the purpose of saving life, every effort should
be made to obtain the controlling agency's and/or the
property owner's consent
If you need entry onto private property in order to search for
an ELT, law enforcement authorities such as local police, the
county sheriff's office or game wardens may be contacted
for assistance.
Normally, local law enforcement officials are happy to
assist you; if they are not familiar with CAP and your
responsibilities, a simple explanation often suffices
If this doesn't work, try having your IC calling AFRCC and
have them explain the situation
Legal Issues
The most important aspect is the manner in
which you approach the matter
 The local civil authorities are in charge, if they tell
you go home, then phone the IC and/or AFRCC
and close the mission

QUESTIONS?
Good Luck and Good
Hunting!
©2000 Scott E. Lanis
115