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© EPA/STR Egypt OUTDebris from crashed Russian jet lies strewn across the sand at the site of the crash, Sinai, Egypt, 31 October 2015. According to reports the Egyptian Government has dispatched more than 45 ambulances to the crash site of the Kogalymavia Metrojet Russian passenger jet, which disappeared from radar after requesting an emergency landing early 31 October, crashing in the mountainous al-Hasanah area of central Sinai. The black box has been recovered at the site.
The jet split in two near the tail, which could mean a 'tail strike' in 2001 was never truly fixed.

The suddenness of what happened to the Russian-operated jet that crashed in the Sinai is highly unusual. According to reports the pilot had reported a technical problem and a diversion to the nearest airport. But the problem was apparently so severe that his plan was overtaken by events and the airplane literally fell out of the sky from its cruise altitude of 31,000 feet.

In theory the Sinai is dangerous air space. Much of the Sinai is a closed military zone where the Egyptian army has frequent skirmishes with Islamic terrorist groups. There have been claims by a jihadist group linked to ISIS that it brought down the flight, but the airplane's altitude put it well beyond the range of shoulder-fired anti-aircraft missiles, or MANPADS, the only relevant weapon fielded by such groups, and first pictures of the wreckage offer no evidence of a missile strike.

Instead investigators will treat as much more credible the possibility of a sudden structural failure. The Airbus A321 was 18 years old, but with a modern airplane like this and regular maintenance that is not in itself a cause for concern.

What does, however, jump out from this particular airplane's record is an accident that it suffered on November 16, 2001 while landing at Cairo (while owned and operated by Middle East Airlines). As it touched down the nose was pointing at too high an angle and the tail hit the tarmac - heavily enough to cause substantial damage.

Tail strikes like this are not uncommon. The airplane was repaired and would have been rigorously inspected then and during subsequent maintenance checks. Nonetheless investigators who will soon have access to the Airbus's flight data recorder will take a hard look at what is called the rear pressure bulkhead, a critical seal in the cabin's pressurization system. Images from the wreckage in the Sinai show parts of the tail and rear fuselage near the site of this bulkhead lying clear of the rest of the debris, suggesting a possible break-up in flight.
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© EPADebris from the cabin section of the crashed Russian jet lies strewn across the sand at the site of the crash, Sinai, Egypt, 31 October 2015.
In the event of a failure of this bulkhead, the airplane would have suffered a sudden and potentially explosive decompression; at its final recorded altitude of 31,000 feet the difference between the pressure inside the cabin and the air outside would have been at the point where such a catastrophic failure would be most likely to occur. The wreckage shows no signs of a fire or an engine-related explosion.

Lufthansa and Air France have announced that they will no longer fly over the Sinai, even though this disaster is almost certainly not a terrorist act.
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© EPADebris from the tail section of the crashed Russian jet lies on the sand at the site of the crash, Sinai, Egypt, 31 October 2015.
I checked the traffic over the Sinai only an hour after the accident was reported. Two corridors were being used, one over the northern Sinai with flights at cruise height of 36,000 feet or more, and a far busier one over southern Sinai with flights at different and often far lower altitudes - some on approach to or departing from Cairo, to the west, some headed for Sharm-el-Sheik, the resort from which the Russian jet departed for St. Petersburg.

Since Malaysian Flight MH17 was brought down by a missile strike over Ukraine, the main flight corridors between Europe, the Middle East, and Asia have been changed to avoid war zones.
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© EPAThe Egyptian Prime Minister, Sherif Ismail (2 - R), examines the wreckage at the site of the Russian plane crash, Sinai, Egypt, 31 October 2015.
The result has been like a highway diversion - much more traffic has been pumped into an alternative route that takes jets over Turkey, Cyprus, and the eastern Mediterranean to a waypoint at Alexandria, Egypt, and then eastward over Cairo, the Sinai and Saudi Arabia to the southern Persian Gulf. There is a major international hub in the Gulf at Dubai, which means that these airlanes are now crowded with long-haul flights routed through Dubai.

Until now the Sinai has not been treated as a war zone, but clearly some airlines are now going to give it a miss. Those that have regular tourist-popular routes into Sharm el-Sheik, like British Airways and Ryanair, have said that they will continue to fly into the southern Sinai. And there is no evidence from the tragedy of the Russian Airbus to suggest that they are wrong.