aircraft communication topic 7 elt, cvr and fdr

AV2220 - Aircraft Communication Systems Chapter 3 1

AVIONICS AVIONICS TECHNOLOGYTECHNOLOGY

Emergency Locator Emergency Locator TransmitterTransmitter

The Emergency Locator Transmitter (ELT) is a self contained battery operated ‑transmitter that is designed to help locate an airplane after a crash. An ELT has an inertia switch that closes in the event of a crash and starts the transmitter emitting a series of down-sweeping tones simultaneously on two emergency frequencies, 121.5 MHz in the VHF band and 243.0 MHz in the UHF band. The battery in an ELT has a design life long enough to operate the transmitter continuously for 48 hours.An emergency locator transmitter (ELT), also referred to as a locator beacon, is required on aircraft: to provide a signal or signals that will enable search aircraft or ground stations to find aircraft that have made crash landings in remote or mountainous areas.



The ELT system is a transmitter that emits an onmidirectional signal on the international distress signals at 121.5 and 243.0 MHz. General-aviation aircraft, commercial aircraft, the FAA, and the CAP (Civil Air Patrol)

monitor 121.5 MHz. The 243.0 MHz is monitored by the military services.

The unit is designed: to automatically activate under emergency condition or may be operated manually from the cabin to summon assistance in other than a

disabling emergency condition, the distress signal can be detected by Search and Rescue Satellite (SARSAT).

ELTs are installed as far aft in the fuselage as it is practical to place them, and they are connected to a flexible whip antenna. The installation must be such that orients the inertia switch so that it is sensitive to a force of approximately 5G along the longitudinal axis of the aircraft.



When an ELT is properly installed, it requires little maintenance other than ensuring that it remains securely mounted and connected to its antenna. There must be no evidence of corrosion, and the battery must be replaced

according to a specific schedule.

Non-rechargeable batteries must be replaced or chargeable batteries recharged: when the transmitter has been used for more than one cumulative hour, or when it has reached 50% of its usable life, or if it is rechargeable 50% of its useful life of charge.

The date required for its replacement must be legibly marked on the outside of the transmitter case and recorded in the aircraft maintenance records.

An ELT can be tested by removing it and taking it into a shielded or screened room to prevent its radiation from causing a false alert.



An operational check may be made with the ELT in the aircraft by removing the antenna and connecting a dummy load.

If it is not possible to use a dummy load: the antenna may be left in place the ELT operated for no more than three audible sweeps the test must be conducted within the first five minutes after any hour

If the ELT must be operated outside of this time frame: the nearest FAA control tower must be contacted and the test coordinated with

them

The pilot should check at the end of each flight to be sure that the ELT has not been triggered. This is done by tuning the VHF receiver to 121.5 MHz and listening for the tone. If

no tone is heard, the ELT is not operating.



The fixed ELT must be installed securely in the aircraft at a location where crash damage will be minimal.

The location selected is usually in the area of the tail cone; In some cabin-type aircraft, the

unit is installed in the aft, top part of the cabin.

Access is provided in either case so the unit can be controlled manually.

System Components

ELT system block diagram



System Components (cont’d)

An ELT transmitter for small airplanes with the antenna and coaxial cable



The ELT system components consist of: Transmitter including adapter plate

and battery Remote control Antenna Wire kit for remote control Antenna cable

System Components (cont’d)

ELT system components location



The ELT is battery powered and is automatically turned on by crash forces. It will transmit a special swept tone for 48 hours on two different emergency frequencies. They are 121.5 MHz and 243.0 MHz; 121.5 is the civilian emergency frequency 243.0 is the military emergency frequency.

It is designed to activate automatically and no preliminary procedures other than proper installation, periodic testing, and specified battery replacement are required. The transmitter is activated by an acceleration operated switch when a rapid deceleration force is applied along the longitudinal axis of the aircraft. The ELT must be installed as far aft as possible but in front of the tail surfaces since this area has been shown to remain intact in most airplane crashes.

System Operation



The batteries in the ELT must be replaced or recharged at specific intervals as required by the FARs.

A typical ELT consists of a self-contained dual-frequency radio transmitter and battery power-supply with a suitable whip antenna. When armed, it will be activated by an impact force of 5g or more, as may be

experienced in a crash landing.

The ELT is powered by the alkaline battery pack.

After a crash landing, the ELT will provide line-of-sight transmission up to 100 mi [161 km] at a receiver altitude of 10,000 ft [3050 m].

The ELT transmits on both distress frequencies simultaneously at 75-mW rated power output for 50 continuous hours in the temperature range of -4 to +131oF [20 to + 55oC].

System Operation (cont’d)



There are times when an aircraft technician may need to test an ELT so he should be familiar with the procedure. If possible, the ELT should be tested with the antenna disconnected or shielded to

prevent the transmission of emergency signals into the air. If this cannot be done, it is still permissible to test the ELT, but only during the

first five minutes of any hour and for three audio sweeps maximum. A VHF communication radio is turned on and tuned to 121.5 MHz. The ELT is then switched on manually until the signal is heard on the receiver and

then switched off again.

System Operation (cont’d)



The ELT function switch, located in the ELT transmitter must be set in ARM position.

The ELT remote control switch, located in the cockpit must be set in ARM position.

The ARM position is the "normal" position for the control switch. In this position, the transmitter will

automatically commence transmitting if the aircraft stops abruptly within defined specification.

There are two forms of manual operations of ELT: Set the ELT function switch to ON

position, or Set the ELT remote control switch to

ON position.Manually operate the ELT only when: A "soft” crash does not activate the

ELT. For very brief periods during

authorized test of transmitter.

Automatic Operation Manual Operation



The control panel on an ELT unit contains a switch with three positions: AUTO, OFF, and ON.

The unit may be tested by tuning the VHF COMM receiver to 121.5 MHz and then placing the ELT switch in the ON position.

The emergency tone will be heard if the ELT is operating.

Immediately after the test, the switch should be returned to the AUTO position.

Set the VHF No. 1 or VHF No. 2 aircraft transceiver to 121.5 MHz with the volume turned up. Turn on the transmitter for 1½ seconds. A repeating downward swept audio

signal should be heard on VHF communication receiver.

Turn the transmitter off after 3 audio sweeps. Move the transmitter switch to ARM position (normal position).

Test Operation



If an ELT is inadvertently turned on, owing to a lightning strike or an exceptionally hard landing, the control switch should be placed

in the OFF position to stop the transmission,

then the switch should be returned to the AUTO position to arm the unit.

Testing of an ELT should be performed within the first 5 minutes of an hour (FAA regulation) and only three pulses of the transmitter should be activated.

For example, a test could be conducted between 1:00 p.m. and 1:05 p.m. with a maximum of three beeps being heard on a frequency of 121.5 MHz. Tests conducted in this manner do

not alert the FAA to a crashed aircraft.

Before this check or test: we should contact the airport control

tower to avoid an unnecessary “alert" or false alarm

coordinate with search and rescue agency since the activate ELT can be detected by the Satellite ground station.

Test Operation (cont’d)



An ELT requires a minimum of service; however, certain procedures are

necessary to assure satisfactory operation.

The battery pack must be changed in accordance with the date stamped on the unit. Typically, the batteries are replaced

every 2 years or after 20 min of continuous use.

The replacement date must be clearly marked on the battery's data plate; otherwise, the battery is not airworthy.

The ELT should be tested regularly to assure satisfactory operation. An inspection of the ELT mounting and antenna should be made periodically to ensure firm attachment to the aircraft.Regulations regarding the operation of ELTs are set forth in FAR Part 91.52. Technicians involved with the

installation and service of ELTs should be familiar with these regulations and manufacturer's data.

Service for an ELT



No person may operate a U.S. registered civil airplane unless it meets the applicable requirements listed below for ELTs.

Each emergency locator transmitter must be in operable condition and meet the requirements of TSO C91 or TSO C91A and it must be installed as far aft as ‑ ‑practicable.

Batteries used in the ELT must be replaced or recharged as appropriate: When the transmitter has been in use for more than one cumulative hour; or When 50% of the useful life has expired.

The expiration date for the replacement or recharge of the battery must be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record.

ELT Regulation

FAR 91.207 Emergency Locator Transmitter



The requirements for ELT do not apply to: A newly acquired aircraft that must be ferried to a place where the ELT will be

installed. An aircraft with an inoperative ELT that must be ferried to a place for ELT repair. Turbojet powered aircraft. Scheduled air carrier flights. Training flights conducted entirely within 50 nautical miles of the airport of operations. Design and test flights. Delivery flights of new aircraft.

FAR 91.207 Emergency Locator Transmitter (cont’d)



The requirements for ELT do not apply to (cont’d): Aircraft engaged in aerial application of chemicals for agricultural purposes. Research and development aircraft. Exhibition and air racing aircraft. Aircraft equipped to carry only one person. An aircraft during any period in which the ELT has been temporarily removed for

inspection, repair, modification or replacement, subject to the following:

A maintenance record entry must be made that includes the date of removal, the serial number and the reason for removal.

A placard must be placed in view of the pilot which states "ELT not installed". The aircraft must not be operated more than 90 days after initial ELT removal.

FAR 91.207 Emergency Locator Transmitter (cont’d)



Cockpit Voice and Flight Cockpit Voice and Flight Data RecorderData Recorder

The cockpit voice recorder (CVR) and the flight data recorder (FDR) are designed to automatically record information in flight that can be used during an investigation following an accident or serious incident.

They are installed on all air carrier jets and some commuter airliners and privately owned aircraft.

The recorders are installed in the aft fuselage as since this area is least likely to be severely damaged in an accident.

A Cockpit Voice Recorder and Flight Data Recorder installed in the aft section of the fuselage



The CVR is designed to record sounds in the cockpit and communications on the intercom and radio systems. It has a hot microphone in the cockpit which is always activated to record voices,

warning sounds, engine noise etc.

The CVR is also connected to the intercom so that conversations between the members of the crew can be recorded. It is also connected to radios so that communications with ATC are recorded.

The CVR has a continuous recording system that holds approximately the last 30 minutes of audio. It is located in the aft fuselage for better survival and it is waterproof and

protected against fire and impact forces.



The flight data recorder has many more inputs than the cockpit voice recorder. It has a recording time of 8 hours on smaller aircraft and about 24 hours on larger

aircraft.

The CVR and FDR are located in the same area of the aft fuselage and have similar protection from water, fire etc.

Air carrier jets have been required to carry CVRs and FDRs for some years, but recently new regulations have gone into effect that require these devices on smaller aircraft.



Multi engine turbine powered airplanes or rotorcraft with 10 passenger seats or more ‑manufactured after October 11, 1991 must have a digital flight data recorder with 8 hours storage.

After October 11, 1991, multi engine turbine powered airplanes and rotorcraft with 6 ‑passenger seats or more and with a required minimum flight crew of 2 pilots must have an approved cockpit voice recorder with minimum storage of 15 minutes.

If an accident or incident occurs, the operator must hold the data 90 days or longer if requested.

Regulation for CVR and FDR

FAR 91.609 Flight Recorders and Cockpit Voice Recorders



The flight recorder required for certain aircraft under FAR 91.609 must record the following items:

1. Airspeed.

2. Altitude.

3. Magnetic Heading.

4. Vertical Acceleration.

5. Longitudinal Acceleration.

6. Pitch Attitude.

7. Roll Attitude.

1. Pitch Trim Position.

2. N1, EPR or Prop RPM and Torque.

3. Vertical Speed.

4. Angle of Attack.

5. Autopilot Engagement.

6. TE Flap Position.

7. LE Flap Position.

8. Reverse Thrust.

9. Spoiler / Speedbrake Position.

Regulation for CVR and FDR (cont’d)

FAR 91 Appendix E: Flight Recorder Specifications



The cockpit voice recorder, or CVR, is an important device for determining the cause of an aircraft accident.

An endless tape allows for 30 minutes of recording, and then it is automatically erased and recorded over.

There are four inputs to the recording heads: The microphones of the captain The microphones of first officer The microphones of flight engineer A microphone that picks up received audio and cockpit conversations

These microphones are always "hot" and do not require any type of keying.

Cockpit Voice Recorder



The pickups are all in the cockpit, but the actual tape recorder is in a fire resistant box usually located near the tail of the aircraft. The CVR is painted bright orange so that it is easily identified among the wreckage.Cockpit voice recorders (CVRs) are very similar to flight data recorders; they look nearly identical and operate in almost the same way. CVRs monitor the last 30 min of flight deck conversations and radio communications. The flight deck conversations are recorded via the microphone monitor panel located on the flight deck.This panel is also used to test the system and erase the tape if so desired. The erase mode of the CVR can be operated only after the aircraft has landed and the parking brake set. Playback is possible only after the recorder is removed from the aircraft.

Cockpit Voice Recorder (cont’d)




Microphone monitor panel for a cockpit voice recorder



In Boeing 737: The cockpit voice recorder uses four independent channels to record cockpit audio

on a 30 minute continuous-loop tape. Recordings older than 30 minutes are automatically erased. One channel records cockpit area conversations using the area microphone. The other channels record any individual audio and transmissions from the pilots

and first observer.

In Boeing 757: The cockpit voice recorder records any transmissions from the cockpit made

through the audio selector panels. It also records cockpit area conversations using an area microphone.




In Boeing 777: It has four-channel solid state voice recorder with flight deck area

microphone records the most recent 30 minutes of flight crew communications.

It erases automatically so that only the last 30 minutes are on the memory tape.

Inputs from the voice recorder are from the area microphone that picks up any conversations on the flight deck, the captains, first officers, and first observer's audio panel and their hot microphones (oxygen mask).





Block diagram of Boeing 777 voice recorder system



Input to the voice recorder is from: the cockpit voice recorder

microphone, the captain's, first officer's, and first observer's audio from their hot

microphone inputs to the AMU.The cockpit voice recorder panel has test and erase buttons and is on the maintenance panel in the flight deck. The cockpit voice recorder microphone is on the overhead panel in the flight deck.

There is a voice recorder jack on the service and APU shutdown panel that permits a ground crew member to monitor flight deck conversation.The recorder unit is in the aft equipment center. It includes an underwater locator

beacon (ULB).To bulk erase the cockpit voice recorder, the airplane must be on the ground and the parking brake set.




Since 1958 any commercial passenger aircraft flying in the United States has been required to be equipped with an automatic flight data recording system. The FAA changed the regulations to include virtually all turboprop aircraft. Today flight data recorders are found on most corporate and all transport-category aircraft.The system must monitor both flight parameters and flight deck voice activities.

Recorded flight parameters include: Aircraft's altitude Airspeed, pitch attitude Roll attitude Magnetic heading Vertical acceleration Flap position Gear position Engine power Greenwich Mean Time

Flight Data Recorder



A flight data recorder is housed in a crushproof container located near the tail section of the aircraft. The tape unit is fire-resistant and contains a radio transmitter to help crash investigators locate the unit under water. A data recorder is typically used for accident investigation; however, some airlines also use

recorded data to aid in troubleshooting recurring mechanical defects.

Flight Data Recorder (cont’d)

A flight data recorder



The tape unit from a flight data recorder

A modern flight data recorder uses a magnetic recording tape to store digital data of flight parameters of the past 25 flight hours. The recorder receives the majority of its input signals from existing sensors located throughout the aircraft. The information is sent to the recording unit, which stores up to 900 bits of information on 1 in. of tape. The tape unit employs: two 4-channel record heads two 4-channel erase heads




One record and one erase head are used when the tape travels from left to right.

The other pair of heads is used when the tape travels from right to left.

The two pairs of erase-record heads are set at different levels (tracks) along the tape, thus producing an 8-track, single-channel format.

This format allows for 25 h of data storage at 3.125 h per track.

The tape reversal and track switching are performed automatically when the tape reaches its limit of travel.


The tape unit from a flight data recorder

aircraft communication topic 7 elt, cvr and fdr

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