By Alex Watts, Sky News
01 April 2014

The mystery of what made flight MH370 crash thousands of miles off route in the middle of the southern Indian Ocean has filled news websites and TV bulletins for the past three weeks.

But despite the huge interest and speculation, are we any nearer to finding out what happened to the doomed Boeing 777 than when it vanished from radar on March 8?

What we do know is both the plane’s transponder and Aircraft Communication Addressing and Reporting System (ACARS), an in-flight digital system that helps track planes after they have gone out of radar coverage, were disabled or stopped working less than an hour into the flight.

The Malaysia Airlines jet carrying 239 people then flew west for at least five hours before crashing somewhere in the Indian Ocean.

Six theories remain for why the plane disappeared – cabin depressurisation, toxic fumes, fire, hijacking, pilot murder-suicide, or simultaneous failures.

A panel of experts – including pilots, airline bosses, manufacturers and regulators – met in central London on Tuesday and tried to throw light on the mystery.

The event, organised by the Royal Aeronautical Society (RAeS), came up with this analysis:

1. The aircraft depressurised but continued to fly

This would explain the initial change in altitude and heading, as well as subsequent lack of communication, but not why the ACARS and transponder were turned off.

The transponder can be turned off from the cockpit and is done routinely when an aircraft lands.

Turning off the ACARS is more complicated, though, and would need someone with systems knowledge going into the aircraft’s avionics bay – but this should have been prevented if security was adequate.

If the plane was depressurised, it would continue to fly automatically until the fuel ran out.

The effect on passengers would vary depending on the altitude. If the aircraft was above 35,000ft, it would take about one minute before everyone was incapacitated.

Oxygen masks should have descended automatically which would work for around 15 minutes.

The flight crew could have lasted longer using oxygen masks, depending on whether they used pure oxygen or an oxygen mix.

SUMMARY: It’s possible.

2. The aircraft was overcome by toxic fumes

The pilots should have been able to send out a distress call and, again, it does not explain why the ACARS and transponder were turned off.

SUMMARY: Unlikely.

3. There was an onboard fire which damaged the communications systems

This would explain the lack of communication, but it is unlikely the aircraft would have then continued to fly as long as it did if the fire continued to burn.

The aircraft’s communication systems could have also been disabled by power failure or sabotage.

Birdstrike is possible, but is unlikely to have caused such damage.

SUMMARY: Unlikely.

4. The aircraft was hijacked

The aircraft was not flown to another destination, nor was it used as a weapon for a suicide terrorist attack.

If it was an individual hijacker, then no one person or motive has been established and, if it was a group, no organisation has claimed responsibility.

SUMMARY: It’s possible.

5. The aircraft was deliberately diverted by the pilot/co-pilot

No reason for this has not been identified. If it was a suicide attempt then why did the aircraft continue to fly for so long?

Another question is why there were no mobile phone calls or texts from passengers or cabin crew, given the in-flight entertainment (IFE) map would have shown the aircraft going off course.

One explanation is the IFE system was turned off.

The second is most passengers were asleep or did not realise anything was wrong until it was too late to do anything. If they tried to phone later, the aircraft would have been in a remote area over the ocean where there was no signal.

The third is passengers and cabin crew may have been incapacitated in some way, such as by hypoxia due to cabin depressurisation.

SUMMARY: It’s possible.

6. Simultaneous failures

One technical expert pointed out that for every plausible scenario, there is at least one contradictory statement.

“If it was hypoxia, then who turned the aircraft?” he asked.

“If it was a fire, then how did it continue flying? If it was the flight crew, then why did the cabin crew not intervene?”

He suggested that, perhaps, more than one scenario occurred simultaneously – such as a wiring fire and depressurisation.

OVERALL SUMMARY: Until more evidence is found, nothing can be proved.