http://aviation-safety.net/database/record.php?id=20131129-0

The real change in the regulation on the use of cockpit doors in flight came about after September 11 attacks, when, in the the chaos that ensued, regulators realised that even if cockpit doors were closed, better laws were needed to prevent unauthorised access to the cockpit.

The motive was that passengers on the United flight 93 which crashed in Pennsylvania had managed to knock down the cockpit door using catering trolleys to get to the terrorists locked inside.

This led to the introduction of compulsory reinforced cockpit doors for aircraft over 45 tonnes and the requirement for cockpit doors to be lockable from the inside.

These relevant changes were introduced in ICAO’s Annex 17 which refers to the corresponding requirement in Annex 6 (Aircraft Operation).

It’s worth mentioning that aircraft under 45 tonnes (including large turboprop aircraft) are still not required to have cockpit reinforced doors and indeed some have no cockpit doors at all.

Having said that, I still believe that cockpit reinforced doors and the requirement for doors to be lockable from the inside became redundant as soon as they were introduced. And this for two primary reasons.

1. The September 11 attacks brought about a complete overhaul in AVSEC regulations. Passengers and employees at airports are screened to far tighter standards by better trained staff using far better equipment.

The probability of prohibited articles which can cause serious injury to a person being introduced on board aircraft is now remote.

Proof of this is that terrorist attacks on aviation since 9/11 were limited to attacks on soft targets (airport public areas, buses etc) or resorted to new and inventive methods to conceal improvised explosive devices.

2. The very events of 9/11 caused a shift in the attitude of passengers towards security. On two separate occasions, two terrorists Richard Reid and Umar Farouk Abdulmutallab who had smuggled IEDs on board transatlantic flights were disabled not by sky marshalls, but by the passengers themselves. It is also not uncommon to hear of passengers who restrain disruptive fellow passengers causing trouble on flights.

It is thus hard to imagine passengers sitting idly by while a terrorist tries to gain access to a cockpit using a hostage.

Rather than “solves that”, it would be more accurate to say “reduces that risk considerably”. The crime that a single person can do on his/her own, could be accomplished by two persons working in tandem.

This is also the reason why crew outside the cockpit can unlock the door by means of a security code, but those within the cockpit can bar it.

It’s to stop a hijacker gaining access by holding a gun to a crew member’s head and forcing him/her to key in the security code (which is how the gunmen got into the Charlie Hebdo offices, you might recall).

The weakness is that they are not kept locked at all times and destructive action by the pilot has not been factored in.

Making it mandatory for two crew members to be in the cockpit at all times solves that.

http://edition.cnn.com/2015/03/26/travel/germanwings-crash-death-by-pilot-cases/