The flight recorder

Dr David Warren of the Aeronautical Research Laboratory at Fishermans Bend, Australia, is credited with inventing the world's first black box flight recorder, in 1953.

He had seen the Minifon, the first miniature tape recorder, at a trade fair at about the time the Comet, the first jet airliner, suffered a series of fatal crashes. He realised that a recorder in the cockpit could keep a record of everything said there.

The Comet accidents Warren responded to happened in 1952 and 1953. In 1956 he designed a crash-survivable prototype called the ARL Flight Memory Unit.

The British Ministry of Aviation later announced that the recorder should be carried on all planes, at first for recording instrument readings.

After the unexplained crash of a Fokker Friendship at Mackay in 1960, the judge at the court of inquiry ordered recorders fitted to all future Australian aircraft. Australia became the first country to require them.

Large airliners carry two recorders. A cockpit voice recorder captures the sounds in the cockpit, and a flight data recorder logs the aircraft's flight data.

Both are installed in the most crash-survivable part of the aircraft, usually the tail section.

A cockpit voice recorder captures crew voices and radio transmissions on 4 channels. Older units recorded on quarter-inch magnetic tape, and newer ones use digital memory chips.

A flight data recorder keeps 25 hours of continuous recording. A cockpit voice recorder keeps 30 minutes, or 2 hours in solid-state digital units.

US airline rules require the flight data recorder's data to be kept until the airplane has been operated for at least 25 hours.

By regulation, newly manufactured aircraft must monitor at least 88 parameters, such as altitude, airspeed, heading and attitude. Some flight data recorders track more than 1,000.

The box is not black. US airworthiness rules require each cockpit voice recorder container and each flight data recorder container to be bright orange or bright yellow.

The container must also carry reflective tape on its external surface to help searchers locate it under water.

Each recorder carries an underwater locator beacon that switches on when immersed in water and transmits at 37.5 kHz.

The beacon runs for 30 days once activated, and its battery has a shelf life of 6 years or more.

Recorders are built to withstand an impact of 3,400 g for 6.5 milliseconds and a fire of 1,100 °C. The NTSB gives the fire duration as 30 minutes.

The container must be mounted to minimise the chance of rupture. It should sit as far aft as practicable, but not where aft-mounted engines could crush it.

An erasable recorder must stop automatically within 10 minutes after crash impact.

A cockpit voice recorder needs an independent backup power source that supplies 10 minutes, plus or minus one minute, of power for the recorder and the area microphone.