AirAsia QZ8501: Air France lessons for missing plane probe

Locator beacon on a flight recorder displayed at Changi airport, Singapore - 29 December Image copyright EPA
Image caption Crash investigators should be able to recover QZ8501's flight recorders relatively quickly

Crashes are often complex. A series of events that on their own wouldn't bring a plane down, yet combined, lead to tragedy.

There are some clues as to what might have caused this AirAsia flight to come down, but we won't know for sure until rescuers retrieve the "black boxes".

There are two on board, normally near the tail which is more likely to survive any impact.

One of the boxes uses microphones to record the sounds from the flight deck.

Not just the voices of the crew, but also important clues, like the sound of the engines (were they straining? was there a bang?), the sound of alarms going off (stall warnings, low level warnings), even the sound of seats being shifted around if the crew were moving about.

The second black box records thousands of pieces of data which tell investigators exactly what the aircraft was doing. Speed, height, power, where the flaps deployed and so on.

It's critical to get all of this information before making judgements, for good reason.

Five years ago a French airliner, flight AF447, also crashed into the sea without sending out a mayday.

Searchers also spotted wreckage days afterwards. And just like the AirAsia flight, they knew the weather had been bad.

Back then, investigators even had some data that had been automatically pinged back to land before the crash, telling them there had been a problem with the aircraft's speed.

Mid-air stall

There is also speculation that the AirAsia plane may have been flying more slowly than normal, although it could be irrelevant because if it was climbing then it would be going more slowly anyway.

Image copyright AFP
Image caption This wreckage from the Air France plane was picked up six days after the crash

But it wasn't until they uncovered the French plane's black boxes more than two years later, buried deep in an underwater mountain range in the Atlantic, that they finally solved the mystery of what happened to flight AF447.

The Air France crash was triggered by bad weather icing up the thin tube that tells the aircraft how fast it's going.

The crew didn't know their speed, but critically, it's the way they handled the problem that eventually crashed the plane. They slowed the aircraft down so much that it stalled in mid air without them realising and dropped out of the sky.

It also transpired that they hadn't been trained to handle the situation they found themselves in. And the alarms on the flight deck were also confusing in a way no-one had anticipated.

The point is, despite several years of speculation and analysis, the final story still surprised everyone, even the experts.

With the AirAsia flight it should be much easier to find the black boxes as they are in much shallower water (30-50m rather than thousands of metres with Air France).

So there should be answers much sooner.

But it once again begs the question: Why is information from all airliner black boxes not streamed in real time to engineers on the ground? If it were, we'd probably have answers already.