The FAA required that the cockpit doors on airliners be locked before take-off on September 11th 2001. How then did hijackers break into locked cockpits in four different planes without any of the eight pilots sounding an alarm over their radios?


Cockpit keys were available to the hijackers in the first-class passenger cabin.

The policy of locking the cockpit door but requiring that keys be left in the passenger cabin arose out of safety concerns and is explained in a 1997 FAA/ National Transportation Safety Board Report A-96-85. After an incident in 1997 in which locked cockpit doors impeded flight attendants from telling the pilots about a smouldering fire, the National Transportation Safety Board (NTSB) found that locked cockpit door presented a hazard because flight attendants might not be able to use interphone link to warn the pilots in the cockpits. To remedy this situation, it asked the FAA to require: " air carriers should either ensure that each flight attendant has a cockpit key in his/her possession during the performance of duties in flight, or that a cockpit key is in a readily accessible place on the aircraft and flight attendants are trained in this location during initial and recurrent training."

So airlines had a choice issuing keys to all flight attendants, which could be lost, stolen or duplicated, or to store cockpit keys in designated place in passenger cabin" convenient to the cockpit."

To avoid the risk of issuing tens of thousands to flight attendants, major airlines, in accordance with the FAA/NTSB recommendation, put cockpit keys for the flight attendants in the first class compartment in containers near cockpit doors. As a "back-up", also in accordance with another FAA/ NTSB recommendation, they gave flight attendants pre- arranged knocking codes to summon the pilots to open the door.
While these measures gave flight attendants the requisite access to locked cockpits, it also provided hijackers with their opportunity. As reconstructed by the FBI, The September 11th conspirators had made at least a dozen reconnaissance flights on Boeing airliners in which they closely observed, and even photographed, the flight crews procedures in the first class compartment. One objective of these conspirators could accomplish would be to pin- pointing the location of the containers for the cockpit keys and learning the back-up pattern of knocks.

Once these conspirators accomplished this reconnaissance mission, the locked cockpit presented no barrier to hijackers.

Collateral question:

If the US government was concerned Al-Qaeda might attempt to seize Airliners in July 2001, what sibgle precaution would have made it far more difficult for the hijackers to get into locked cockpits?