Large commercial aircraft (over 12 500 pounds) are required to be equipped with a flight data recorder (FDR) and a cockpit voice recorder (CVR). These recorders are frequently called the "black boxes".
The CVR records radio transmissions and the acoustic environment in the cockpit, notably internal communications between the pilots and sounds such as engine noises.
The FDR records numerous parameters that can be used to assess the aircraft's trajectory, attitude, control inputs, and the status of systems. Typical parameters include altitude, airspeed and heading.
All recorders on commercial aircraft today use digital technology to record the flight data onto magnetic tape or solid-state memory chips. All new recorders use solid-state memory chips.
Both recorders are typically installed in the tail of the aircraft: this section is the most likely to remain intact in an accident. The recorders are designed to survive high impact forces (3400g) and high temperatures (1100ºC). Each recorder is equipped with an underwater locator beacon or "pinger," which activates when immersed in water and transmits an acoustic signal for 30 days.
The Transportation Safety Board of Canada (TSB) conducts the readout and analysis of the black boxes from aviation accidents and incidents in Canada. The TSB Engineering Laboratory in Ottawa has designed and developed sophisticated software systems to extract and analyze recorder information. Interactive three-dimensional graphics simulations assimilate large amounts of information to aid investigators.
Under the TSB's legislation, the information contained on CVRs is considered to be privileged and can only be released by the Board when the Board considers it necessary in the interests of transportation safety.
The information from flight recorders is paramount in determining the sequence of events and understanding the circumstances leading up to an accident.