Q&A: New York air crash

An American Airlines plane has crashed near New York's John F Kennedy airport after one of its engines reportedly separated from the fuselage. BBC transport correspondent Simon Montague assesses the evidence so far.

Q: What can we tell at this stage?

A: We can't tell anything for certain at all. Eyewitnesses have given accounts of having seen an engine fall off. Normally one has to view eyewitness accounts with a great deal of doubt, but on this occasion there also seems to be what looks like part of an engine that has landed at a petrol station some distance from the main crash, so that does seem to lend some support to the theory that an engine or part of an engine did fall off the aircraft shortly after takeoff.

Q: How likely is it for an engine to fall of an aircraft?

It's extremely unusual for an engine to fall off an aircraft

A: It's extremely unusual for an engine to fall off an aircraft but it does occasionally happen. In fact American Airlines had an incident back in 1979 when an engine fell off a DC10 near Chicago. The aircraft crashed with the loss of all 271 people on board and at that time it was America's worst ever air accident. Why the engine fell off, if indeed it did at all is something that would have to be explored by the accident investigators.

Q: Would the plane automatically crash if the engine did fall off?

A: What the experts say is that modern aircraft of this size are designed to cope with engine failure on takeoff and that this aircraft should in theory have been able to keep flying despite what appears to have been the loss of one of its two engines and they are rather puzzled that the aircraft crashed. They say it must have been a particularly critical stage of the takeoff, perhaps when it was only just off the ground or perhaps when the undercarriage was still down.

Q: Could this have been an accident?

Whether it was terrorist action or some kind of malfunction it's not clear

A: One of the mysteries at the moment is that there doesn't appear to have been any communication from the pilots of the aircraft that they had forseen any kind of trouble. Yet at the same time we're hearing the American government saying that it does appear to be some kind of accident. Well that suggests that perhaps it was a very sudden accident but you would still expect there to be some kind of communication from the crew.

Q: What will investigators be looking at now?

A: One of the key things will be for investigators to discover the two aircraft data recorders. There's the cockpit voice recorder which should have on it all the verbal communications between the pilots and air traffic control and then there's the flight data recorder - which has already been found - that records a wide range of parameters about the aircraft, such as what angle it was flying at what height it was flying at etc. From these the investigators should be able to create pretty exactly how the aircraft was being flown and what went wrong and at what stage.

Q: What about reports of an explosion?

A: We're getting all sorts of reports at the moment. On the one hand the government saying it's apparently an accident on the other hand the FBI saying there appears to have been an explosion but whether it was terrorist action or some kind of malfunction it's not clear. While a lot of reports are focusing on an engine falling off one doesn't actually know whether that's the cause of the crash or the consequence of something else happening on the plane.