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Mission Aircrew Course Electronic Search Patterns (APR 2010). 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). Aircrew Tasks.

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Presentation Transcript
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)

Aircrew Tasks
objectives
Discuss the various types of ELTs.

Describe how an ELT can be detected.

Describe how the aircraft DF works in both the Alarm and DF modes.

Discuss using the DF during a typical ELT search

Response during initial phase, including signal fade

Response when getting close

Response as you pass over the beacon

Objectives
objectives4
Describe the following ELT search methods:

Homing

Wing null

Aural

Signal

Discuss signal reflection and interference.

Describe how to silence an ELT and the legal issues involved.

Objectives
slide5

Emergency Locator Transmitter Direction Finding for Aircrews:use of equipment commonly found in CAP aircraft

N98987

©2000 Scott E. Lanis

5

objective the elusive elt
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 MHz (third generation advanced ELT/EPIRB/PLB)

General types:

General aviation aircraft

Military (“beepers” or “beacons”)

Marine EPIRB

Personal Locator Beacons (PLBs)

Advanced (406)

Test station (training practice beacon)

The ELT
most aircraft have elts installed
Most aircraft have ELTs installed

But they don’t always survive a crash

most aircraft have elts installed10
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 most likely have a 243.0 MHz beacon

Some downed pilots may be able to communicate via two-way radio on 243.0 MHz using a PRC-90 military survival radio

Beacon mode transmits like an ELT on 243 MHz

You can monitor (and track!) this frequency on your aircraft’s DF unit

Military beacons
personal beacons
Personal Locator Beacon (PLB)

Sometimes “Personal Emergency Transmitter” (PET)

Intended for hikers, hunters, boaters, and other remote wilderness travelers

MOST Use a 406 MHz transmitter and a 121.5 MHz homing signal (generally, at only 25 milliwatts)

Many are also equipped with a built-in GPS receiver that provides lat/long coordinates

Each PLB must be registered with NOAA

Personal beacons
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

By law, all must be 406 capable now

Marine EPIRB
advanced elts
Designed to operate with SARSAT/COSPAS

406 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 matched to a registration database

The owner's name, address and type of aircraft is obtained from database, so AFRCC can call to see if the aircraft is really missing (70% resolved this way)

Since geostationary satellites process the digital signal, it will be heard more quickly and allow a much faster response

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

Not mandatory in the United States; MAY become mandatory in Canada

Advanced ELTs
practice beacon
Training Beacons are registered as Test Stations, and referred to as “Practice Beacons”

Includes ones used by CAP

All practice beacons should operate on 121.775 MHz (if it uses another frequency, don’t use it)

During practice searches, avoid calling the practice beacon an ‘ELT’ when communicating over the radio

May cause confusion

Always use the term ‘Practice Beacon’

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

Testing an Aircraft ELT
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

Inadvertent Activation
false alarms
At least 97%+ of received ELT signals are false alarms

Historically, for 121.5 MHz ELTs about 1 in 1000 are actual emergencies

For 406 MHz ELTs about 1 in 10 are actual emergencies

They block emergency communications on 121.5 and 243.0 MHz (guarded by towers, ARTCC, and the military)

False Alarms
initial elt detection
Initial ELT Detection
  • Until 1 Feb 2009, most ELTs were initially detected by the SARSAT-COSPAS system
  • This system no longer monitors 121.5 and 243.0
  • SARSAT-COSPAS only listens for 406 MHz signals now
  • Initial detection for an ELT must come from an airborne or surface-based asset
    • Airliners, military aircraft, ATC facilities
    • Participating civil traffic: YOU
  • Using the Area of Intersection method should get you closer, you may need mission staff to assist
slide22

GOES 406 ELT Detection

GEO Footprint

LEO Footprint

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!

OK, So How Should I Treat an ELT Mission?
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

Locating the ELT Signal
direction finder df
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
L-Tronics DF

Normal: Alarm toggle in ‘up’ position

DF: toggle is ‘down’

df antenna
DF Antenna

These are mounted on the bottom, but may be on top

step 1 acquire the signal
Step 1: Acquire the Signal

To hear the signal you can use your L-Tronics receiver, the Becker DF, or one of the comm radios

To acquire with a comm radio, turn the squelch OFF

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 Intersection Area

Or to the SARSAT hit (406 ELT) if you have one

or to the point designated by your incident commander

©2000 Scott E. Lanis

29

beginning the search altitude selection
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

SIGNAL

HEARD!

NO SIGNAL

NO SIGNAL

ELT

©2000 Scott E. Lanis

30

altitude selection
Altitude Selection

©2000 Scott E. Lanis

31

step 2 track df the signal
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

33

wing shadowing
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

34

wing shadowing antennas
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

35

communications antennas above the wing
Communications Antennas Above the Wing

Antennas Abovethe Wing

N98987

©2000 Scott E. Lanis

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df antennas below the wing
DF Antennas Below the Wing

N98987

Antennas Belowthe Wing

©2000 Scott E. Lanis

37

how to df by wing shadowing also called wing null method
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

315

45

E

W

225

135

S

©2000 Scott E. Lanis

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wing shadowing signal blocking for antennas above the wings
Wing Shadowing:Signal BlockingFor Antennas Above the Wings

NULL

NULL

NULL

SIGNAL

ELT

©2000 Scott E. Lanis

40

wing shadowing antennas above the wing
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 the90º index

W

315

225

N

S

45

135

E

ELT

©2000 Scott E. Lanis

41

wing shadowing signal blocking for antennas below the wings
Wing Shadowing: Signal BlockingFor Antennas Below the Wings

ELT

NULL

NULL

SIGNAL

NULL

©2000 Scott E. Lanis

42

wing shadowing antennas below the wing
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

S

225

135

W

E

315

45

N

ELT

©2000 Scott E. Lanis

43

aural hearing search method
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

44

aural search
Aural Search

©2000 Scott E. Lanis

45

metered search build fade method
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 in strength, turn 180º

©2000 Scott E. Lanis

46

metered search
Metered Search

3

2

FADE

6

4

ELT

7

8

2

MAXIMUM SIGNAL

THEN DROP

5

9

MAXIMUM

6

8

7

4

SIGNAL

6

5

4

5

4

2

1

FIRST SIGNAL

2

©2000 Scott E. Lanis

47

left right df homing
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

48

l tronics df types
L-Tronics DF Types

Single Meter Model

Dual Meter Model

mSENS ®VOL

REC

243

ALARM

AUX

DF

121.775

121.6

VHF-DF

OFF

121.5

L-Tronics

DF

STRENGTH

mSENS ®VOL

ALARM

243

AUX

121.775

121.6

VHFDF

OFF

121.5

L-Tronics

©2000 Scott E. Lanis

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frequency switch
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

mSENS ®VOL

REC

243

ALARM

AUX

DF

121.775

121.6

VHF-DF

OFF

121.5

L-Tronics

©2000 Scott E. Lanis

50

mode switch
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

mSENS ®VOL

REC

243

ALARM

AUX

DF

121.775

121.6

VHF-DF

OFF

121.5

L-Tronics

©2000 Scott E. Lanis

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volume sensitivity
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: half-scale, 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

STRENGTH

mSENS ®VOL

ALARM

243

AUX

121.775

121.6

VHFDF

OFF

121.5

L-Tronics

©2000 Scott E. Lanis

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df settings for single meter models
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

53

df settings for dual meter models
DF SETTINGS FORDUAL 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

54

pre flight functional check
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

55

six steps
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

56

step 1 receive
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

57

receive mode strength window
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
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

59

step 3 df
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

60

a direction finding primer antenna theory
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 antenna62
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

N98987

Antennas Belowthe Wing

Antenna Elements

antenna reception pattern
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

2

3

©2000 Scott E. Lanis

63

df unit antenna pattern
DF Unit Antenna Pattern

REFLECTOR

ELEMENTS

TOP VIEW

DIRECTIONAL

ANTENNA

PATTERN

RECEIVING

ELEMENT

AIRCRAFT VIEW

direction finding mode window
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
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

66

df centers
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
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

68

ambiguity
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 1)

ELT (Possibility 2)

df needle
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 thenpoint LEFT

The needle always points Direct to Follow the Target!

ELT

solving ambiguity
SOLVING AMBIGUITY

Actual ELT positionis unknown to user

Make a small turn left or right

As a teachingreminder, “Use aTURN to TELL”

ELT (Possibility 1)

ELT (Possibility 2)

solving ambiguity72
SOLVING AMBIGUITY

Actual ELT positionis unknown to user

Make a small turn left or right

As a teachingreminder, “Use aTURN to TELL”

Example:

TURN LEFT

needle goes left

ELT (Possibility 1)

ELT (Possibility 2)

solving ambiguity73
SOLVING AMBIGUITY

Actual ELT positionis unknown to user

Make a small turn left or right

As a teachingreminder, “Use aTURN to TELL”

Example:

TURN LEFT

If needle goes left

ELT is to your left (behind you)

ELT (Possibility 2)

solving ambiguity74
SOLVING AMBIGUITY

If you turn Left and theneedle moves Right

The ELT is inFront of you!

ELT (Possibility 1)

ELT (Possibility 2)

solving ambiguity75
SOLVING AMBIGUITY

If you turn Left and theneedle moves Right

The ELT is inFront of you!

Example:

Turn left

Needle goes right

ELT (Possibility 1)

ELT (Possibility 2)

solving ambiguity76
SOLVING AMBIGUITY

Solution:

If you turn Left and the needle moves Right

The ELT is inFront of you!

ELT (Possibility 1)

step 6 shoot
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

N

315

45

E

W

225

135

S

©2000 Scott E. Lanis

77

how a l tronics df unit works summary
How A L-Tronics DF Unit Works: Summary

Two Main Modes of Operation

RECeive

DF

RECeive Mode is a Strength Meter

Left is low, right is high

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

reflections
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

80

beating reflections
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 bearing-or try that at the first sign of problems!

©2000 Scott E. Lanis

81

carrier only signals
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

©2000 Scott E. Lanis

82

carrier only signals83
Carrier-Only Signals

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 the IC and let the controlling agency troubleshoot the problem.

©2000 Scott E. Lanis

83

vertical reflections signal dropout
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

84

signal dropout
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

85

signal strength
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

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signal strength rate of change
Signal Strength Rate of Change

©2000 Scott E. Lanis

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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

Cone of

Confusion

©2000 Scott E. Lanis

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reception in the cone of silence
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

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pinpointing the elt
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 angleseach time, remembering that your path may be curved due to wind (like uncorrected NDB holding)

The point where station passage is received several timesshould be the location of the target

2

3

1

©2000 Scott E. Lanis

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pinpointing the elt91
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

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becker sar df 517
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
Becker Operation

Power

Mode

Page

Tune

Squelch

DF

Locate

power
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)

slide96
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

slide97
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

slide98
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

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

Squelch Knob

Squelch Setting Triangle

Ambient Noise Level

df direction find
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
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

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

The dark marble should be fairly stable on an actual signal because of signal-averaging software

DARK MARBLE

>020>

CLEAR MARBLES

locate
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
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
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

becker thoughts105
Becker Thoughts

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 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

Air-to-ground is CAP’s best unique ES skill!

©2000 Scott E. Lanis

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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?

DF upon Landing
little l per
Six Steps

Receive

Half

DF

Center

Turn

Shoot

Little L-Per
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

OK, which of these planes is it in?
how to body shield the null
How To Body Shield: The 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

NULL!

SIGNAL

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

Airmobile UDF Team 101
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 push-plate 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.

OK, where is the thing?(IN the aircraft!)
silencing the elt
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 elt114
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)

Silencing the ELT

®® 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
legal issues116
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
legal issues117
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

Legal Issues