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Mission Aircrew Mission Aircrew CourseCourse
Chapter 10: Electronic Chapter 10: Electronic Search PatternsSearch Patterns
(Mar 2007)(Mar 2007)
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 TasksAircrew Tasks
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
ObjectivesObjectives
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}
ObjectivesObjectives
©2000 Scott E. Lanis 5
Emergency Locator Emergency Locator TransmitterTransmitter
Direction Finding for Direction Finding for Aircrews:Aircrews:
use of equipment commonly use of equipment commonly found in CAP aircraftfound in CAP aircraft
N98987N98987
©2000 Scott E. Lanis 6
Objective: The Objective: The Elusive ELTElusive 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!
Wave Sound
Click Icon to Hear an 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)
The The ELTELT
ELT ELT AntennaAntenna
Most aircraft have ELTs Most aircraft have ELTs installedinstalled
But they But they don’t don’t
always always survive a survive a
crashcrash
Most aircraft have ELTs Most aircraft have ELTs installedinstalled
But they But they don’t don’t
always always survive a survive a
crashcrash
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
Military Military beaconsbeacons
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
Personal Personal beaconsbeacons
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
Marine Marine EPIRBEPIRB
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)
Advanced Advanced ELTsELTs
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’
Practice Practice BeaconBeacon
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 Testing an Aircraft ELTAircraft ELT
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 Inadvertent ActivationActivation
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)
False False AlarmsAlarms
Detection Detection TimelineTimeline
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 five-minute detection/alert
Accuracy of Accuracy of SARSAT/COSPSARSAT/COSP
ASAS
SARSAT VideoSARSAT Video
QUESTIONSQUESTIONS??
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 OK, So How Should I Treat an ELT Mission?Treat an ELT Mission?
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 Locating the ELT SignalSignal
Direction Finder Direction Finder (DF)(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 L-Tronics DFDF
Normal: Alarm toggle in ‘up’ position DF: toggle is ‘down’
DF DF AntennaAntenna
These are mounted on the bottom, but may be on top
©2000 Scott E. Lanis 29
Step 1: Acquire the Step 1: Acquire the SignalSignal
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 30
NO SIGNAL
SIGNALSIGNALHEARD!HEARD!
NO SIGNALELT
Beginning The Search: Beginning The Search: Altitude SelectionAltitude 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
31©2000 Scott E. Lanis
ELT RECEPTION DISTANCE
0
5000
10000
15000
20000
25000
30000
35000
40000
0 18 30 34 56 69 95 121
147
200
265
DISTANCE, Nautical Miles
ALT
ITU
DE
, Fe
et
AG
L
Altitude Altitude SelectionSelection
©2000 Scott E. Lanis 32
Step 2: Track (DF) the Step 2: Track (DF) the SignalSignal
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 Wing ShadowingShadowing
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: Wing Shadowing: AntennasAntennas
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 Communications Antennas Antennas
Above the WingAbove the Wing
N98987N98987
Antennas Abovethe Wing
©2000 Scott E. Lanis 36
DF Antennas Below the DF Antennas Below the WingWing
N98987N98987
Antennas Belowthe Wing
QUESTIONS?
©2000 Scott E. Lanis 38
How To DF by Wing How To DF by Wing ShadowingShadowing
(Also Called Wing-Null (Also Called Wing-Null Method)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
SE
W
45
135
225
315
©2000 Scott E. Lanis 39
Wing Shadowing:Wing Shadowing:Signal BlockingSignal Blocking
For Antennas Above the For Antennas Above the WingsWings
SIGNAL
ELT
NULL
NULL
NULL
©2000 Scott E. Lanis 40
Wing Shadowing:Wing Shadowing:Antennas Above the Antennas Above the
WingWing
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
N
S
E
W
45135
225
315
ELT
©2000 Scott E. Lanis 41
Wing Shadowing: Wing Shadowing: Signal BlockingSignal Blocking
For Antennas Below the For Antennas Below the WingsWings
SIGNAL
ELT
NULL
NULL
NULL
©2000 Scott E. Lanis 42
Wing Wing Shadowing:Shadowing:
Antennas Below the Antennas Below the WingWing
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
N
S
E
W
45
135
225
315
ELT
©2000 Scott E. Lanis 43
Aural (Hearing) Search Aural (Hearing) Search MethodMethod
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 SearchAural SearchEqual signal strength circle:barely audible signal in aircraftreceiver at search altitude
chord 1
chord 2
chord
3
ELTcommence low altitude patterndescending
SIGNALFADES
SIGNALHEARD
SIGNALHEARD
SIGNALHEARD
SIGNALFADES
©2000 Scott E. Lanis 45
Metered SearchMetered Search(Build & Fade) (Build & Fade)
MethodMethod
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 SearchMetered Search
FADE
MAXIMUM
SIGNAL
MAXIMUM SIGNALTHEN DROP
FIRST SIGNAL1
2
3
4
5
6
ELT
2
2
2
4
4
4
6
6
7
8
7
8
95
5
©2000 Scott E. Lanis 47
Left-Right DF Left-Right DF HomingHoming
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 L-Tronics DF TypesTypes
Single Meter Model
Dual Meter Model
L-Tronics
ALARM
OFF
243
121.6
121.775 AUX
121.5
SENS VOL
VHFDF
DF STRENGTH
L-Tronics
ALARM
OFF
SENS VOL
VHF-DF
243
121.6
121.775 AUX
121.5
DF
REC
©2000 Scott E. Lanis 49
Frequency Frequency SwitchSwitch
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
L-Tronics
ALARM
OFF
SENS VOL
VHF-DF
243
121.6
121.775 AUX
121.5
DF
REC
©2000 Scott E. Lanis 50
Mode Mode SwitchSwitch
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
L-Tronics
ALARM
OFF
SENS VOL
VHF-DF
243
121.6
121.775 AUX
121.5
DF
REC
©2000 Scott E. Lanis 51
Volume & Volume & SensitivitySensitivity
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
L-Tronics
ALARM
OFF
243
121.6
121.775 AUX
121.5
SENS VOL
VHFDF
DF STRENGTH
©2000 Scott E. Lanis 52
DF SETTINGS FOR DF SETTINGS FOR SINGLE METER SINGLE METER
MODELSMODELS
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 FORDF SETTINGS FORDUAL METER DUAL METER
MODELSMODELS
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 PRE-FLIGHT FUNCTIONAL CHECKFUNCTIONAL 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 SIX STEPSSTEPS
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: Step 1: RECeiveRECeive
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)
RECeive RECeive Mode/STRENGTH Mode/STRENGTH
WindowWindow
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
©2000 Scott E. Lanis 58
Step 2: Step 2: HALFHALF
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: Step 3: DFDF
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)
A Direction Finding Primer:A Direction Finding Primer:Antenna TheoryAntenna 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 DF AntennaAntenna
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
Antenna Elements
N98987N98987
Antennas Belowthe Wing
©2000 Scott E. Lanis 62
Antenna Reception Antenna Reception PatternPattern
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
DF Unit Antenna PatternDF Unit Antenna Pattern
AIRCRAFT VIEW
TOP VIEW
RECEIVINGELEMENT
REFLECTORELEMENTS
DIRECTIONALANTENNAPATTERN
Direction Direction Finding Finding
Mode/WindowMode/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!
©2000 Scott E. Lanis 65
Step 4: Step 4: TURNTURN
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
DF DF CENTERSCENTERS
AlternatingAntennaPatterns
AlternatingAntennaPatterns
WHEN THE PATTERNS
ARE EQUAL, THE DF NEEDLE
CENTERS!
ELT (Possibility 1)
ELT (Possibility 2)
©2000 Scott E. Lanis 67
Step 5: Step 5: CHECKCHECK
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
AMBIGUITAMBIGUITYY
ELT (Possibility 1)
ELT (Possibility 2)
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!)
DF DF NEEDLENEEDLE
ELT
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!
SOLVING SOLVING AMBIGUITAMBIGUIT
YY
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 SOLVING AMBIGUITYAMBIGUITY
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 SOLVING AMBIGUITAMBIGUIT
YY
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 SOLVING AMBIGUITAMBIGUIT
YY
If you turn Left and theneedle moves Right
The ELT is inFront of you!
ELT (Possibility 1)
ELT (Possibility 2)
SOLVING SOLVING AMBIGUITAMBIGUIT
YY
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 SOLVING AMBIGUITAMBIGUIT
YY
Solution:• If you turn Left
and the needle moves Right
• The ELT is inFront of you!
ELT (Possibility 1)
©2000 Scott E. Lanis 76
Step 6: Step 6: SHOOTSHOOT
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
SE
W
45135
225
315
How A L-Tronics DF Unit How A L-Tronics DF Unit Works: Summary 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
QUESTIONS?
©2000 Scott E. Lanis 79
ReflectioReflectionsns
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 Beating ReflectionsReflections
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 Carrier-Only SignalsSignals
• 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 the IC and let the controlling agency troubleshoot the problem.
©2000 Scott E. Lanis 82
Vertical Vertical Reflections & Reflections &
Signal DropoutSignal 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 83
Signal Signal Dropout 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 SIGNALNO SIGNAL
SIGNALSIGNALHEARDHEARD
©2000 Scott E. Lanis 84
Signal Signal StrengthStrength
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 85
Signal Strength Rate of Signal Strength Rate of ChangeChange
©2000 Scott E. Lanis 86
Cone of Cone of ConfusionConfusion
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 ofConfusion
©2000 Scott E. Lanis 87
Reception in the Reception in the “Cone of Silence”“Cone of Silence”
antenna
GOOD
POOR
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
©2000 Scott E. Lanis 88
Pinpointing the Pinpointing the ELTELT
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
1
2
3
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Pinpointing the Pinpointing the ELTELT
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
QUESTIONS?
Becker SAR-DF 517Becker 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 OperationBecker Operation
PowerModePageTuneSquelchDFLocate
PowerPower
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)
ModeMode
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
PagePage
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
TuneTune
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
SquelchSquelch
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 Squelch Setting TriangleTriangle
Ambient Noise Ambient Noise LevelLevel
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 Becker Direction Finding NotesNotes
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
>020>
DARK MARBLE
CLEAR MARBLES
LocateLocate
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 Bearing on More than One TransmitterOne 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 ThoughtsBecker 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
©2000 Scott E. Lanis 103
After Locating The After Locating The ELTELT
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!
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 DF upon LandingLanding
Six Steps•Receive•Half•DF•Center•Turn•Shoot
Little L-Little L-PerPer
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 OK, which of these planes is it in?it in?
How To Body Shield: How To Body Shield: The NullThe Null
NULL!
ELT 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
SIGNAL
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 101Airmobile UDF Team 101
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 OK, where is the thing?thing?
(IN the aircraft!)(IN the aircraft!)
Silencing the ELTSilencing 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
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 Silencing the ELTELT
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 #
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 Legal IssuesIssues
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 Legal IssuesIssues
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 Legal IssuesIssues
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QUESTIONS?QUESTIONS?
Good Luck and Good Luck and Good Hunting!Good Hunting!