Did Anti-Terror Cockpit Doors Lead To Alps Crash?

Reinforced cockpit doors were introduced to lock out potential terrorists to keep passengers safe - but they may have led to the Germanwings Alps crash.

Until the September 11 attacks in 2001, doors to the flight deck could be opened from both sides, and were often flimsy enough to be forced open with a kick or a shoulder barge.

Since then, commercial airliners have reinforced the doors - often with bulletproof Kevlar - and made them impossible to open from the outside.

The New York Times quotes a senior military source involved in the investigation as saying that one of the two pilots may have left the cockpit and then been unable to get back in.

That means that if the pilot who remained in the cockpit was incapacitated, through ill-health for example, the plane would have been flying without anyone controlling it.

Some reports have suggested that the door could have been faulty but Airbus says this is "pure speculation".

It was one of the theories put forward for the disappearance of Malaysian Airlines Flight MH370 which disappeared from radar screens over the China Sea.

And in 2013 LAM Mozambique Airlines flight with 27 passengers and six crew on board crashed in Namibia.

The investigation found that the captain had a clear intention to crash the Embraer 190 aircraft, with the cockpit voice recorder capturing repeated loud bangs on the cockpit door from the co-pilot who was locked out of the flight deck until shortly before the crash.

On an Airbus, the pilots have a section on their control panel with a switch to lock and unlock the door.

Usually, a flight attendant will telephone the pilot before being given access, however, if there is no response a secret code can be entered which triggers an emergency unlocking procedure.

Aviation Expert Captain Rusty Aimer told Sky News that the doors are known as "fortress doors" with strong, complicated designs.

In January a Delta Air Lines flight was forced to make an emergency landing after a pilot was accidentally locked out of the cockpit.

The door malfunctioned leaving the first officer to land the plane at McCarran International Airport in Las Vegas.

Other theories as to why the German plane crashed include:

:: Explosive Decompression

The inside of an Airbus A320 is pressurised to the equivalent height of 8,000 feet - the air at the cruising altitude of 30,000 feet is impossible for humans to survive for long due to how thin it is.

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