Max Kingsley Jones, an aviation expert at Flight International magazine, answered questions for BBC News Online on what may have gone wrong:

The suggestions are the aircraft decompressed - is this a reasonable assumption?

Yes, it is one possible scenario, given the circumstances.

What happens during decompression?

Sudden decompression is very violent, with the air in the cabin being rapidly sucked out through a puncture in the fuselage. It's a bit like air rushing out of a balloon.

When cabin air pressure falls below normal levels (either rapidly or gradually), a pressure warning horn or klaxon will normally sound in the cockpit.

What courses of action are available to pilots in such an event?

To don oxygen masks, execute rapid descent to a safe altitude (10-15,000ft), and inform the Air Training Corp (ATC).

Can this type of event occur in big passenger aircraft and what are the procedures when this happens?

Yes. Pilot procedure is same as above, while passengers will be provided with drop-down oxygen masks in the cabin.

How would air traffic control have discovered the problem?

The Learjet was not responding to radio calls and diverted from the course filed in its flight plan.

What is the safety record of the Lear jet?

Some 1,800 Learjets (all models) are in service worldwide, with the first aircraft being delivered in 1964. To date, around 60 aircraft have been destroyed in fatal crashes, where crew and/or passengers were killed.