Who, what, why: How often do planes fly over conflict zones?

The crash of Malaysian airliner MH17 in eastern Ukraine has raised questions about which conflict zones commercial jets will fly over. Who decides where is safe to fly, asks Tom de Castella.

Most of the decisions about a route are taken by airlines. But they must avoid no-fly zones. The area where the Malaysian airliner crashed had a no-fly zone in place up to 32,000ft (9,754m). The airliner was flying at 33,000ft (10,058m).

There are also national aviation bodies to consider. For example, the US's Federal Aviation Administration in April issued a Notam (notice to airmen) that prohibited US airliners from flying over the Crimean region of Ukraine and nearby areas of the Black Sea and the Sea of Azov. After the crash of MH17 it widened that to cover the whole of Ukraine.

British Airways has been avoiding eastern Ukraine for some time, the BBC understands. But many airlines continued to fly over it. According to Flight radar24, which monitors live flight paths, the airlines that most frequently flew over Donetsk in eastern Ukraine in the last week were: Aeroflot 86 (flights), Singapore Airlines 75, Ukraine International Airlines 62, Lufthansa 56, and Malaysian 48. It was not necessarily a risky approach. The chance of a rocket reaching above 32,000 feet was considered remote, says Sylvia Spruck Wrigley, author of Why Planes Crash.

The UK's Civil Aviation Authority says airlines' decisions will be based on a range of factors - advice from the Foreign Office, warnings in the area, weather, navigation aids, strikes and which airports are out of action. They will generally fly the shortest route - a long detour around a warzone will cause delay and add extra fuel costs.

Selected flights over east Ukraine on the afternoon of 17 July

Airlines fly over most trouble spots, says Mikael Robertsson, co-founder of Flight radar24. They have to get from A to B in the most efficient manner possible. Syria is probably the only airspace that everyone avoids. Other trouble spots - North Korea and Somalia - airliners do fly over, he says, although it is hard to verify how common this is.

A pilot told the Guardian that "We would often avoid areas where there is air-to-air conflict, but we flew over Iraq and Afghanistan when the British and US armed forces were deployed there, because only one side was using military jets."

After the attack: Airliners avoid eastern Ukraine

Airlines tend to be secretive about operational details, perhaps for security reasons. BA says that it will not give "further details" on its routes, adding: "Some parts of the world are closed to commercial airline operations and we would never fly in airspace unless we were satisfied that it was safe to do so." It still flies to Ukraine, although not over the east of the country.

Qantas would only say: "We don't fly over the Ukraine. For London to Dubai we fly 400 nautical miles south of the region."

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