Barrier must withstand ramming force of 136kg food trolley but open in event of a pressure loss

Decompression requirements are emerging as the key challenge for companies trying to develop long-term secure flightdeck door designs in the wake of the 11 September terrorist attack on the US.

The fundamental problem is to design a door that can withstand the ramming force of a 136kg- (300lb) plus food trolley, while remaining capable of instantly opening large sections or vents in the case of sudden cabin or cockpit depressurisation. The retrofit market for the door is estimated at $2 billion and may affect 10,000 commercial aircraft worldwide.

According to Boeing figures, there have been over 600 decompressions in commercial jet transport history. In evidence given to a hearing of a US House and Senate subcommittee recently the manufacturer says around 300 incidents have been severe enough to require use of oxygen masks.

"Approximately 50 were rapid decompressions that could stress the structure. Only two of those led to accidents," the company adds.


Despite the decompression risk, the US Federal Aviation Administration has been forced by the urgency of the situation to grant a 180-day waiver on this airworthiness requirement to US airlines for the installation of simple cockpit-door crossbar locking devices, augmented by deadbolts and strengthened hinges.

Among those developing the devices are American Airlines, Butler National and a Timco Engineered Systems and AIM Aviation joint venture.

Manufacturers plan to use radical new concepts to comply with FAR Part 25.365governing the capacity of the door to provide an instantaneous decompression path between the flightdeck and passenger compartments.

Flight Structures & Integration (FSI), part of B/E Aerospace, received FAA approval on 10 October for its design. It includes a strengthened, bullet-resistant cockpit door, bulkhead barrier and security camera system.

Although approved as a long-term solution, the FAA is believed to have granted FSI the go-ahead for its design, based on the short-term waiver guidelines to enable the manufacturer to use the current supplemental type certificate (STC) rather than having to wait for up to a year longer for a future STC.

The design, details of which remain confidential until it receives a patent on its entry and locking system, will be available by January.

"The FAA's concern is with an explosive decompression and subsequent catastrophic event," says the company. "It is worried it could create dangerous load paths, as the cockpit door could suddenly become an internal pressure bulkhead."

The system is thought to be based on a set of quick-release bolts possibly triggered by a static pressure system to open panels and vents in the event of decompression. With the bolts in place, however, the door will be sufficiently strong to repel even a determined attack.

To verify its ballistic tolerance, FSI has tested the structure against a variety of calibres including heavy calibre 0.357in Magnums.

Texas-based Avcom Technologies, is also developing its "Guardian Door" concept featuring reinforced latches and a set of large vents around the edge of the door to meet the requirement.

Airbus and Boeing are also thought to be studying new approaches based on work in progress to counter the growingnumber of air rage incidents.

Airlines have 180 days to file a refit plan with the FAA and the work must be completed on all aircraft by March 2003.

Source: Flight International