As the search continues for the missing Malaysia Airlines flight MH 370, which disappeared over the ocean somewhere south of Vietnam while on route from Kula Lumpur to Beijing during the weekend, most reports have concentrated on the possibility of terrorism.
But there are also many other possible reasons why a fully laden plane carrying 239 passengers might go missing in mid-flight – here are eight of them.
1. Catastrophic failure of the plane’s airframe. However, most experts believe this unlikely given the plane’s safety record.
2. A bomb. A distinct possibility in this case. Pan Am Flight 103 was a transatlantic from Frankfurt to Detroit via London and New York that was destroyed by a terrorist bomb on Wednesday, 21 December 1988, killing all 243 passengers and 16 crew.
3. Hijacking. Used many times in the past by terror groups, hijacking usually results in the targeted plane landing somewhere before demands are made in return for the release of the passengers. There is no evidence to suggest this but a hijacking gone wrong cannot be discounted.
4. Engine failure. A failure of both the plane’s Rolls Royce engines is a possibility but many experts think this unlikely because a plane can glide for around 20 minutes giving the pilots' time to make a mayday call which didn’t happen.
5. Storms. Bad weather can bring down a plane but most modern aircraft are built to take the additional stresses of storms and the weather during the missing plane’s flight was reportedly clear.
6. Suicide. Planes have crashed in the past when their pilots decided to end their own lives and the lives of their passengers. A Silkair flight and an EgyptAir flight during the 1990s are believed to have crashed in this way.
7. Military action. Passenger aircraft have been shot down by military planes. A Korean Airlines flight was shot down in 1983 by a Russian jet fighter and an Iran Air flight was shot down by a US warship in 1988.
8. Pilot error. Again, this has happened before when pilots have become disoriented and allowed the plane to go off course. But it is unlikely because the missing plane would have been picked up by radar from the surrounding countries.