Cockpit Voice Recorder (CVR) & Flight Data Recorder (FDR)

Introduction

The principal function of a Cockpit Voice Recorder (CVR) system is to preserve, in the event of an air accident, vital information that is recoverable for use by the Accident Investigation Branch (AIB).

The CVR automatically records the last 30 minutes (2 hours on some aircraft) of communications and conversations on the flight deck. It is operational whenever 115 volts AC power is applied to the aircraft, any engine is running, or the aircraft is airborne.

The system comprises a tape recorder, a control unit, a monitor display and an area microphone.

Commercial aircraft have a flight recorder which records various aircraft parameters during the entire duration of the flight. The main function of the flight data recorder (FDR) is to preserve the aircraft data in order to determine the cause of any aircraft accident. It is also used to gather information for trend analysis and troubleshooting.

In smaller aircraft the FDR may be combined with a cockpit voice recorder.

Cockpit Voice Recorder (CVR)

The Joint Aviation Authority requires that all multi-engine turbine-powered aircraft with a maximum take-off weight in excess of 5700 kg and with seating for more than nine passengers shall be equipped with a cockpit voice

recorder. The voice recorder must be capable of retaining recorded information over the period of the last 2 hours of operation and the parameters recorded must be as follows:

All radio voice communications received or transmitted from the flight deck.
All sounds within the flight deck environment, including audio signals received by each boom and mask microphone in use.
Voice communications between flight crew members on the interphone systems.
All voice or audio signals identifying navigation or approach aids, as received on crew headphones or speakers.
All announcements made by the flight crew on the public address system.

For aircraft with a maximum take-off weight of less than 5700 kg the recording time may be limited to 30 minutes.

The cockpit voice recorder must automatically begin recording before the aircraft first moves under its own power and continue until it is no longer capable of moving under its own power. In practical terms, this is usually from first engine start to last engine shut-down.

The voice recorder container must be easy to locate in a crash situation by painting it a distinctive orange or yellow colour with reflective material attached and it must be resistant to shock, heat and fire.

On the front of the unit is fitted an underwater locating device (ULD), that will emit a continuous series of ultrasonic pulses to help locate a submerged CVR. The unit is automatically activated by water and the battery will last several days.

The recorder must be installed in a location where its recordings are least likely to suffer damage. The site chosen is usually as far aft as practicable, typically close to the rear pressure bulkhead. It must receive its electrical power from a bus bar that can be relied upon to continue providing power under all circumstances and that is separate from the aircraft's essential and emergency services.

Control Unit

This is mounted on the flight deck, usually in the roof panel. It contains monitoring and testing circuitry and also the area microphone to pick up general flight deck conversations and sounds. It has the following controls:

AUTO / ON

When the switch is in the AUTO position the CVR will start to record when the first engine is started and will stop 5 minutes after the last engine is shut down. Selection of the ON position starts the CVR recording immediately and latches the switch in the ON position until first engine start, when it will click back to AUTO.

CVR TEST

Pressing the TEST button activates an extensive set of functional tests which determine the integrity of the system using the BITE (built-in test equipment) facility. A successful self-test results in a visual ‘good’ indication (a status deflection needle or a status LED).

ERASE

Erasure of the tapes is only possible with the aircraft on the ground, all engines stopped and the parking brake set. Suitable safety interlocks are installed to prevent inadvertent or airborne tape erasure. Additionally the erase button must be held depressed for at least 2 seconds before the circuit activates.

Some CVR control units will incorporate the area microphone, which are 'HOT MIC'.

CVR CONTROL PANEL

Flight Data Recorder (FDR)

The Joint Aviation Authority (JAA) requires that all turbine powered aircraft with a take-off weight greater than 5700 kg and with seating for more than nine passengers shall be equipped with a flight data recorder. The device must be capable of retaining data recorded during at least the last 25 hours of aircraft operation, although this figure may be reduced to 10 hours for aircraft with a take-off weight of less than 5700 kg.

The data recorded must be sufficient to establish the following flight parameters:

Altitude
Airspeed
Heading
Attitude in pitch and roll
Acceleration
Thrust or power on each engine
Configuration of lift or drag devices
Radio transmission keying
Use of automatic flight control systems
Angle of attack
Air temperature

For aircraft with a take-off weight in excess of 27 000 kg it is required that additional data must be recorded in order to be able to establish the following parameters, as well as those listed above:

Primary flight control positions
Pitch trim
Primary navigation information as displayed to the flight crew
Flight deck warnings
Landing gear position
Radio altitude

The data recorded must be from essentially the same sources as those which supply the information displayed to the flight crew and it must include any parameters that are peculiar to the operating characteristics of the aircraft design.

The flight data recorder must automatically begin recording all the above data before the aircraft is capable of moving under its own power and must automatically cease recording after the aircraft is no longer capable of moving under its own power. In practical terms, this usually means that recording starts with start of the first engine and ceases at shutdown of the last engine. The recorder must be contained within a container painted in a distinctive orange or yellow colour and its recovery must be assisted by reflective material and an underwater locating device that is automatically activated upon immersion.

It must be so installed in the aircraft that the probability of damage to the recorded data from shock, heat or fire is minimised. This is usually satisfied by locating the flight data recorder as far aft as practicable, typically in the vicinity of the rear pressure bulkhead.

The electrical supply to the recorder must be from a bus bar that can be expected to provide power under all circumstances, without jeopardising essential or emergency services. There must also be a pre-flight testing facility to check the serviceability of the recorder.

Types of flight data recorder

Flight data recorders are classified according to the amount of information to be retained and the length of aircraft operating time over which data are to be recorded and stored. Recorders meeting the JAR-OPS requirements for

aircraft with a maximum take-off weight in excess of 27000 kg must be capable of recording at least 32 parameters and these are classified as Type I flight data recorders. Type II recorders meet the JAR-OPS requirements for smaller aircraft (take-off weight of 5700 kg) and these must be capable of recording at least 15 parameters. Type IIA recorders only have a 30-minute recording span, but must be capable of retaining data recorded during the preceding take-off.

The minimum 32 parameters required of Type I flight data recorders are listed below. Normally a Type II recorder would record the first 15 of these parameters, although the parameters may vary according to aircraft type.

UTC or elapsed time
Pressure altitude
Indicated airspeed
Heading
Vertical acceleration
Pitch attitude
Roll attitude
Radio transmission keying
Power on each engine
Trailing edge flap position or control selection
Leading edge flap position or control selection
Thrust reverser position
Ground spoiler and/or speed brake position
Outside air temperature
Autopilot, autothrottle and automatic flight control system modes and status
Longitudinal acceleration
Lateral acceleration
Primary control surface positions and/or pilot's control inputs
Pitch trim setting
Radio altitude
Glide path deviation
Localiser deviation
Marker beacon transit
Master warnings
Navigational radio frequencies
DME distances
Landing gear status from squat switch
Landing gear selector position
GPWS
Angle of attack
Hydraulics systems pressures
Latitude and longitude, ground speed and drift angle

System monitoring

The flight data recorder system has its own built-in test equipment (BITE) and the serviceability of this and the recorder should be checked before the first flight of the day. FDRs are subject to annual inspection and to calibration on a 5-year cycle. Dedicated airspeed and altitude sensing equipment is subject to bi-annual inspection and calibration.

Aircraft Integrated Data System

Many of the larger transport aircraft types are equipped with data gathering and retention systems for monitoring the health and performance of the engines and aircraft systems. The system most commonly used is known as the aircraft integrated data system (AIDS), which provides the option of a real time display of current operating conditions, or downloading and print- out of the data when the aircraft is on the ground.

Some operators make use of an extension to AIDS known as the aircraft communication addressing and reporting system (ACARS), whereby the system can be interrogated from the operator's ground base and technical data downloaded whilst the aircraft is in flight. The data recorded and stored by AIDS can be interchanged with the flight data recorder and the FDR data can be printed out during aircraft maintenance.