What happened
On 23 July 2002, a Beech 200 Super King Air, registration G-OWAX, was cruising at FL190 while performing a passenger flight from Oxford to Amsterdam. During the flight, approximately 12 nm north-east of Clacton, Essex, the crew heard a loud bang and a hissing sound, accompanied by fogging in the cabin. The crew confirmed a rapid decompression by observing the climbing cabin altitude and subsequently initiated a descent to FL90. After transmitting a PAN call, the aircraft returned to Oxford. Upon landing, the crew found the main cabin door could not be opened, necessitating the evacuation of the 8 passengers and 2 crew through the emergency exit.
The investigation
The investigation focused on the mechanical failure of the door and the failure of the emergency oxygen system to deploy. Regarding the oxygen system, it was discovered that the system had not been armed. The crew believed the system was active because the arming knob on G-OWlar was positioned in a way that appeared to be the ON position. However, due to a non-standard installation, the knob sat three inches proud of its mounting even when in the OFF position, leading the pilots to misinterpret its status.
Examination of the main cabin door revealed that a pin within the rear upper roller assembly had migrated from its intended position. This movement allowed the roller to exit its slot, removing the necessary support for the lock bolt. Consequently, the internal cabin pressure forced the bolt into the surrounding structure, allowing the door to separate slightly and causing the loss of pressurization. The investigation also noted that the operating rod within the door had become distorted during the incident, which prevented the door from being opened after landing.
Findings
- The primary cause of the decompression was the migration of a pin in the door's roller assembly, which allowed the lock bolt to be displaced by cabin pressure.
- The crew did not manually deploy the emergency oxygen because they believed the system was already armed.
- The oxygen arming knob on this specific aircraft was installed in a manner that differed from the crew's previous experience, making the OFF position appear to be the ON position.
- The pin migration likely occurred over an extended period.
Safety action
- Safety Recommendation 2003-36: It is recommended that the Federal Aviation Administration and Raytheon Aircraft Company review the inspection requirements or the securing method for the main cabin door latch roller assembly on Beech 200 aircraft to prevent pin migration.