The secrets of the indestructible black box and the mysteries it has solved

IN MAY 1953 a de Havilland Comet jet aircraft, operated by British carrier BOAC, crashed near Calcutta killing all 43 people on board.

missing plane, black box, secrets, mysteries, location, help, solve, problem, Malaysian Boeing 777, missing, jet, data, recorder, family, relativesA black box could hold the answer to the missing Malaysian Boeing 777 plane[AP]

The plane was on its way from Singapore to London and the dead included a senior Australian politician travelling with his wife to represent the state of Victoria at the Queen's Coronation, as well as 10 guests also bound for the ceremony.

One of those called to investigate the tragedy - a gruesome early milestone of the jet age - was a young Australian fuel chemist called David Warren, whose father had died in an unexplained plane crash 19 years earlier.

For him the Indian crash was a mystery "without any explanation, without any witness, without any survivors".

Around the same time he saw a small pocket recorder at a trade show and started to think about the use to which such a device could be put.

"If a businessman had been using one of these in the plane and we could find it in the wreckage and play it back, we'd say, 'We know what caused this'," he later recalled.

He went on to develop the flight data recorder (FDR), better known as the "black box".

It got that nickname not because of its colour - it's actually bright orange to make it easier to find at a crash site - but because of its seemingly mysterious properties.

Designed to withstand jet fuel fires and massive water pressure, the recorder is now the first thing investigators look for if a plane crashes.

It remains the best hope of finding out what happened to Malaysian Airlines flight MH370 which disappeared on March 8 and is now assumed to have crashed into the southern Indian Ocean.

Given that the battery on the recorder's locator beacon lasts only about a month, the news that the Australian defence vessel Ocean Shield has detected a signal consistent with transmissions from the plane's black box has come just in time.

The FDR itself records air speed, altitude, vertical acceleration and fuel flow.

Its discovery would reveal whether or not the doomed plane climbed for some reason to an altitude at which passengers and crew lost consciousness, as one theory suggests, thereby explaining why it flew on for hours in the wrong direction without transmitting any kind of distress messages.

 Inventor David Warren with his flight data recorder [EPA]

Sometimes the mistrust is so great that the veracity of the black box recording becomes suspect

The black box also contains the simple piece of kit that inspired Warren's invention: the cockpit voice recorder (CVR) on a permanent loop that tapes the last half hour or so of flights.

This is the element that might tell us what was going on aboard the Malaysian plane in human terms: was the cockpit stormed?

Was the pilot on some kind of suicide mission?

It also satisfies our morbid fascination with what it was actually like to be there, creating a kind of real-life dramatisation of the events that have caught the world's horrified imagination.

That fascination was the rationale behind an American documentary play called Charlie Victor Romeo (the codename for CVR) devised by a New York theatre group in the late 1990s.

Using the black boxes from six air crashes between 1985 and 1996, actors recreated the moments when the crew realised what was happening to their plane.

It may sound like bad-taste voyeurism but aviation experts and military officials flocked to the play and the US Air Force recorded a performance for educational purposes.

Mercifully, disaster sometimes happens before the victims know what has hit them.

That was the case in Britain's worst air disaster, when Pan Am Flight 103 dropped out of the sky over Lockerbie on December 21, 1988, killing all 259 people on board and 11 on the ground.

The CVR recorded a loud noise consistent with an explosion.

This could be used alongside radar data that showed the wreckage spreading for more than a mile within eight seconds, building up a picture of the bomb smuggled aboard.

In other cases just being able to hear what was going on in the cockpit gives solace to grieving relatives.

After United Flight 93 crashed in Pennsylvania on September 11, 2001 - the only one of four planes hijacked by Al Qaeda that did not reach its intended target - families asked to be allowed to hear the actual tape.

The FBI initially refused but eventually changed its mind and agreed to play the tape at a confidential meeting.

Even then, the black box helped fuel conspiracy theories.

Families were told the voice recorder stopped at 10.03am, but seismic data indicated that the plane hit the ground at 10.06am.

 Devastated families have no clue what has happened to their loved ones who went missing on March 8 [GETTY]

Was the discrepancy evidence of some kind of cover-up, boosting the theory that the US Air Force had shot the aircraft down to prevent the terrorists crashing it into the White House or the Capitol Building in Washington DC?

It was just as likely to be a synchronisation error on one of the recording devices either on the aircraft or on the ground.

But the supposed time lag remains unexplained.

Sometimes the mistrust is so great that the veracity of the black box recording becomes suspect.

That's what happened with South African Airways Flight 295 - a Boeing 747 named Helderberg - that crashed into the Indian Ocean in 1987 killing all 159 crew and passengers.

A report by the post-apartheid Truth and Reconciliation Commission found there was a belief among SAA pilots that passenger flights were being used to transport armaments, and there was speculation that a fire on board the plane may have been connected to the country's nuclear programme.

This speculation was fuelled by reports that the pilot could be heard on the CVR referring to "deadly material" on board but, amid accusations of a cover-up by the aviation authorities both before and after the fall of apartheid, it wasn't even certain that the recording was genuine.

With other aviation crashes the explanation provided by the black box is much more prosaic.

The closest recent parallel to the Malaysian Airlines mystery is Air France Flight 447 from Rio de Janeiro to Paris, which went missing with 228 people on board in June 2009.

It vanished somewhere over the Atlantic, beyond the reach of radar, and for five days its fate was a complete puzzle.

Once the black box was recovered the harrowing last conversation - "Damn it, we're going to crash… this can't be happening!" - indicated the autopilot had packed up suddenly after a thunderstorm.

Then the crew responded incorrectly to cockpit readings and put the aircraft into a stall from which it could not recover.

It was a case of simple human error with catastrophic consequences.

But in the case of the Malaysian plane the CVR may be the least interesting element in the black box.

At the moment the likeliest explanation for its erratic course is that around the time it ceased communications something happened to make the passengers and crew lose consciousness.

The plane then flew on for hours in the wrong direction before it ran out of fuel and dropped out of the sky on the wrong side of Australia.

If that's the case the cockpit recorder will have wiped over the most interesting part of the tape and the final half hour will just be the sound of the plane flying on unattended to its doom.

But for the bereaved families, that may be the most comforting sound of all.

It would at least confirm that the ill-fated passengers were unaware of what was about to hit them as the plane began to plummet into the watery depths.