What happened
On 28 July 2012, a Beech B200 Super King Air, registration OO-LET, was performing aerial communications relay duties over London in support of the 2012 Olympic Games. While operating in the London TMA at FL240, the aircraft experienced a sudden and progressive failure of nearly all electrical equipment. The crew, consisting of two pilots and two technicians, noted that fuel gauges indicated zero and the Mode C transponder signal was lost.
In an attempt to manage the emergency, the pilot flying (PF) turned off the engine anti-ice system and attempted to restore power by cycling the generators and battery switches. The crew eventually navigated visually towards Cambridge Airport. Due to the lack of electrical power, the crew could not verify the landing gear position via the cockpit annunciators. They initiated the manual landing gear extension procedure using the hydraulic hand pump. During the approach, the pilot stopped pumping the handle upon feeling heavy resistance, fearing potential damage to the mechanism.
Upon touchdown at Cambridge Airport, the landing gear collapsed. The aircraft slid along the runway for approximately 400 meters, causing extensive damage to the propellers, engines, undercarriage doors, and the luggage pod. There were no injuries to the four crew members on board.
The investigation
The AAIB examined the aircraft after it was recovered to a hangar. Testing of the aircraft battery showed it was fully discharged. While the investigation could not pinpoint the exact cause of the electrical failure, the starter/generators were found to be in good working order during subsequent tests.
Investigators also examined the landing gear system. Although the pilot had omitted to pull the landing gear relay circuit breaker, the investigation concluded this was unlikely to have caused the collapse. The inspection revealed that the hydraulic lines remained intact and no components of the gear itself had broken. However, the investigation noted that the crew's decision to stop pumping the handle was influenced by conflicting mental models of different landing gear systems.
Findings
- The primary cause of the gear collapse was likely that the crew ceased operating the alternate extension handle before the landing gear was fully extended and locked.
- The crew's inability to confirm the gear status was due to the total electrical failure, which rendered the gear-down annunciators inoperable.
- The pilot's decision to stop pumping the handle was driven by a fear of damaging the system, a concern reinforced by the presence of different landing gear systems in the crew's regular fleet.
- The abnormal procedures for the hydraulic system on OO-LET did not provide warnings regarding the consequences of continued pumping once the gear was locked, unlike the mechanical system used on other aircraft the crew frequently operated.