Air crash investigations centre on finding the "black boxes" - the data collection devices mounted in the tail of an aircraft.

Click here to see a diagram of modern flight data recorder

Under internationally agreed regulations, commercial aircraft must carry the equipment to record the performance and the condition of the aircraft in flight.

Survivor: The data recorder from the 1996 TWA 800 disaster

The recorders are housed in immensely strong materials, such as titanium, and insulated to withstand a crash impact many times the force of gravity, temperatures of more than 1,000C for up to 30 minutes and the immense pressure of lying on the seabed.

One manufacturing test for data recorders involves firing them from a cannon into a wall to simulate an aircraft suffering a catastrophic crash landing while travelling at hundreds of miles an hour.

The recording material is itself insulated against accidental deletion and the corrosive effects of sea water.

Modern black boxes, which are actually orange, record up to 300 factors of flight including:

• Airspeed and altitude
• Heading and vertical acceleration
• Aircraft pitch
• Cockpit conversations
• Radio communications

The safety precautions are designed to ensure, theoretically, that accident investigators will be able to recover the recorders, compile a full picture of an aircraft's last moments from the recordings and then accurately explain what went wrong.

Origins

Australia lays claim to the development of the flight recorder after one of its scientists dreamed up the concept following the birth of commercial jet aircraft in the 1950s.

Simple but effective: First recorders monitored few factors

In 1953, jet flight experts were struggling to understand why a number of Comet airliners had inexplicably crashed, throwing the entire prospect of commercial jet air travel into doubt.

A year later Dr David Warren, an Australian aviation scientist, proposed a flight recording device and by 1958 he had produced the prototype "ARL Flight Memory Unit".

That first version was slightly larger than an adult hand but capable of recording some four hours of cockpit conversation and instrument readings.

To Dr Warren's surprise, the device was at first rejected by aviation authorities as having "little immediate direct use in civil aircraft" while pilots described it as a "Big Brother" spying on their actions.

On taking the device to the UK, Dr Warren was enthusiastically received and, following a BBC report on the device, manufacturers came forward to take over the project.

Similar developments had by this stage also begun in the United States and by 1960 the first steps were being taken to make the devices mandatory.

Computers have now replaced magnetic tape, meaning the devices can record more data and are far more likely to survive an impact.

Black and white archive pictures courtesy of the Australian Department of Defence.

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