Explosion, systems failure caused crash
The loss of a Malaysia Airlines Boeing 777 over the South China Sea on Saturday was almost certainly caused by a catastrophic explosion or failure.
The clues are telling. No mayday from the crew and the 777 dropped off the radar in a second, indicating a failure of all systems.
Mercifully, the passengers would have likely known little, with most being knocked out by the intensity of the explosion or the G- forces of the upset.
There are only a few scenarios that could cause such devastation - a bomb, the loss of a cargo door, failure of the rear pressure bulkhead or the loss of a wing or tail.
A bomb brought down Pan Am Flight 103 over Scotland in 1988, killing all 243 passengers and 16 crew on board.
But while the initial focus is on a bomb carried aboard by passengers or loaded as cargo, a structural failure is a more likely cause.
The lost 777 was involved in a serious accident at Shanghai's Pudong International Airport in August 2012 that damaged its right wing.
It was preparing for take-off to Kuala Lumpur when its wing struck the tail of a China Eastern A340-600 with such force that it sheared off and was left embedded in the A340's tail.
The 777 was repaired and returned to service but it is possible that the damage done was more serious than just losing the wing tip.
Aviation history is littered with "minor" incidents that develop into tragedies several years later.
In 1979, an American DC-10 crashed at Chicago Airport when a pylon that attaches the engine to the wing failed and the engine ripped away from the plane.
Investigators found there was a crack in the pylon that was caused by an unauthorised maintenance procedure.
The worst single crash in the history of aviation was the result of a faulty repair to the rear pressure bulkhead of a Japan Airlines 747 that took seven years to fail.
The JAL 747 was involved in a landing accident in June 1978 at Osaka and sustained substantial damage to the rear underside of its fuselage. The rear pressure bulkhead was also cracked.
The plane was repaired and engineers replaced the lower part of the rear fuselage and a portion of the lower half of the bulkhead.
On August 12, 1985, the repair failed and the tail of the 747 ripped away.
The loss of the tail and hydraulic lines left the pilot helpless and the 747 crashed, killing 520 of the 524 aboard.
Pilot error is also a possibility in the loss of the 777.
The Air France disaster, when an Airbus 330 plunged into the Atlantic Ocean in 2009, killing 228, was a combination of faulty sensors and inadequately trained pilots.
Fire is an unlikely cause because the 777 would not have disappeared so quickly and it would have been very likely that the pilots would have sent out a distress call.
Another possibility, albeit remote, is a software glitch.
Malaysia Airlines had a serious incident in August 2005 with a 777 flying from Perth to Kuala Lumpur.
Flying at 11,500m about 30 minutes after takeoff, the 777's software incorrectly measured speed and acceleration, causing it to suddenly shoot up 1000m.
The pilot disengaged the autopilot and descended and landed safely back in Perth.
Other possibilities include it being hijacked or accidentally shot down.
It may take search and rescue teams days, if not weeks, to locate the plane and it might take investigators years to work out what caused the crash.
