Aviation Sri Lanka 



Black Box

Cockpit Voice Recorders (CVR) and Flight Data Recorders (FDR)

All commercial aircraft are required by the FAA to be equipped with two "black boxes" that record information about a flight. Both recorders (CVR and FDR) are installed to help reconstruct the events leading to an aircraft accident. The CVR (Cockpit Voice Recorder), records radio transmissions and sounds in the cockpit, such as the pilot's voices and engine noises. The FDR (Flight Data Recorder), monitors parameters such as altitude, airspeed and heading. The newer versions of CVR and FDR use digital storage technology. Both recorders are installed in the most crash survivable part of the aircraft, usually the tail section. Each recorder is equipped with an Underwater Locator Beacon (ULB) to assist in locating in the event of an over water accident. The device called a "pinger", is activated when the recorder is immersed in water. It transmits an acoustical signal on 37.5 KHz that is up to a depth of 14,000 feet.  

Although named 'Blackboxes', flight recorders are painted orange with added reflective strips to make them easily recognizable.


They are usually placed at the rear of the aircraft, as this is the section of the plane which is the least damaged in the event of a crash

 The Flight Recorder is placed at the rear of the aircraft, surrounded by padding

 An opened Flight Data Recorder

 Flight recorders which are ready to be installed

Cross section of a recoder


Impact prevention method to protect the recorder


The industry is presently developing specifications for recording of CNS/ATM systems information that, although not currently recorded, may be desirable to be stored in crash survivable recorders on-board the aircraft. Examples include:

CNS/ATM digital data link (replacing the historical voice radio link),

Cockpit Video,

Increasing number of mandatory flight parameters 

Navigation and Surveillance information (future systems).

Direct Digital Audio Inputs (in lieu of analog conversion and sampling)

There is continuing debate within industry on the benefits of adding some of these new information sources to the airborne crash survivable recorders. As already discussed, combining Flight Data and Cockpit Voice within a single unit is relatively simple, but may be quickly obsoleted by any future recording legislation.

Solid State Digital Data Recorder (SSDDR) System

In this proposed new system the crash survivable recorders are reduced to simply recording digital information received on high-speed serial interface(s). The recorders need not know the specific source or type of information being recorded, but simply recording the digital data as it is received under a yet to be defined rule set. The processing of information and digitization would therefore take place in other avionics within the aircraft and transmitted to the redundant recorders. If developed suitably, this architecture can provide the following benefits:

1) Dual redundant Crash Survivable Recorders - Reduces airlines spares and logistic support and provides improved probability of 100% data recovery.

2) Crash survivable recorder need not require modification to meet changes in recording requirements.

3) Lower system cost - data processing and digitization process moved to highly integrated avionics subsystems (instead of the recorders themselves, which are subject to more severe operating environments)

4) Minimizing Installation costs by reducing wiring required for growth systems.

5) Eliminating the need to add other crash survivable recorders for additional information storage

6) Minimize cost impact for the recorder itself. The price of two redundant recorders would only be on the order of 50% more than the total price of today's separate FDR/CVR combination.

In this architecture, the crash survivable recorders need sufficient memory capacity and input bandwidth to handle current and future requirements.

Following an accident, both recorders are immediately removed from the accident site and taken into the custody of department of civil aviation authority. Using sophisticated computer and audio equipment; the information stored on the recorders is extracted and translated into an understandable format. Depending on the situation of the accident backups of the recoding is taken.


The Cockpit Voice Recorder

The CVR records the flight crew's voices, as well as other sounds inside the cockpit. The recorder's "cockpit area microphone" is usually located on the overhead instrument panel between the two pilots. Sounds of interest to an investigator could be engine noise, stall warnings, landing gear extension and retraction, and other clicks and pops. From these sounds, parameters such as engine rpm, system failures, speed, and the time at which certain events occur can often be determined. Communications with Air Traffic Control, automated radio weather briefings and conversation between the pilots and ground or cabin crew are also recorded. During the investigation the aviation, authorities create a written transcript of the tape to be used. The captain of an aircraft has the authority to erase the CVR contents if he believes the particular aircraft has not involved in such situation that an investigation to be carried out. This is mainly because of the CVR recodes all the personal dialogs among the cockpit crew and further exposes their privacy. CVR installed on aircraft including helicopters shall have a capability of retaining the information recorded during at least the last 30 minutes of their operation and also the CVR shall not be switched off  during flight time.

From 1st January 2005 all aircraft including helicopter equipped to utilize digital communication and required to carry a cockpit voice recorder shall record on the cockpit voice recorder or the flight data recorder the digital communications with Air Traffic Service (ATS).


Air traffic control tapes (both radar and voice) with their associated time codes are also used to help determine the local standard time of one or more events during the accident sequence. These times are applied to the transcript, which provides a local time for every event on the transcript. This transcript contains all pertinent portions of the recording. The actual transcript of air crash KLM and Panam is available at the home page and you can pause the scrolling transcript by mouse clicking it. 

The CVR recordings are treated differently than the other information obtained in an accident investigation. Due to the highly sensitive nature of the verbal communications inside the cockpit, and the content and timing of release of the written transcript are strictly regulated.


The Flight Data Recorder
FDR can store 5 to 300 numbers of parameters for a period 25 hours continuously while CVR can store 4 voice channels.

Here are a few of the parameters recorded by most FDRs:




Pressure altitude




Vertical acceleration


Magnetic heading


Control-column position


Rudder-pedal position


Control-wheel position


Horizontal stabilizer


Fuel flow


FDR has impact tolerance of 3400Gs /6.5ms and fire resistance of 1100 degC/30 min. The FDR and CVR withstand a water pressure resistance up to a level of 20,000 ft. Battery of FDR and CVR has 6 years of shelf life. 

Best selling books about Black Boxes (Click  for details)