Introduction
On 28 July 2012, a Beech B200 Super King Air, registration OO-LET, was involved in an accident at Cambridge Airport. The aircraft was engaged in aerial work, providing communications relay for the 2012 Olympic Games. The crew consisted of two pilots and two technicians. No passengers were on board. No injuries were reported. The aircraft sustained extensive damage to the propellers, engines, undercarriage doors, and luggage pod.
History of the Flight
The aircraft was returning to Cambridge Airport after completing an airborne communications relay task over London. It was operating in the London TMA at FL240 in VMC. This was the second flight of the day for both the aircraft and crew. After completing the task, the pilots prepared to return. ATC cleared the aircraft to descend to FL180 and route to the BKY VOR. The co-pilot, who was pilot flying (PF) from the left seat, selected engine anti-ice on to provide additional drag for the descent, and the pilots commenced the Descent checklist. Due to cockpit workload, neither pilot recalled seeing anti-ice annunciations or the inertial vane bypass doors extend.
During the checklist, the PF noticed the fuel gauges indicating zero. Almost immediately, ATC informed the pilots that the Mode C transponder readout was no longer received. The commander transmitted a possible electrical problem, but no further radio communication occurred. The last Mode C readout was at FL183.
Electrical Failure
Over the next two to three minutes, the pilots experienced progressive failure of all electrical equipment except the left instrument panel Electronic Flight Information System display, which remained powered by a backup supply. However, the display gave erroneous information, so pilots turned it off. The abnormal checklist did not cover a total electrical failure, so the PF turned both generators and the battery switch off and on again in an attempt to restore power. He also selected the alternate inverter, and the PNF recycled cabin power switches. The PF did not attempt to select generators to RESET. The left panel had functioning ASI and VSI; the right panel had a working vacuum-driven attitude indicator, ASI and altimeter. Engine rpm gauges and standby compass remained operational. Both pilots saw no warning lights on the annunciator panel and were not wearing sunglasses. Technicians reported seeing the AC frequency gauge oscillate full-scale deflection. The PF turned off the engine anti-ice but couldn't recall when.
Mindful of avoiding a security alert during the Olympic Games, the crew executed the pre-briefed communications failure procedure, turning the aircraft onto a northerly heading to clear the London TMA, then proceeding towards a designated holding area.
Approach and Landing
As the aircraft approached Wisbech, the commander recognized land features. The aircraft descended to 5,000 ft, and the crew visually navigated towards Cambridge Airport. Concerned about fuel endurance due to inoperative fuel gauges, they circled the airport to alert ATC. The crew then carried out the Landing Gear Manual Extension procedure. During this, they operated the landing gear control handle but omitted to pull the landing gear relay circuit breaker. The PF operated the alternate extension handle. Initially easy, the handle met heavy resistance, and the PF stopped to avoid damaging the system. The PNF checked the resistance, and the PF continued pumping on downwind and base legs, stopping each time heavy resistance was felt.
The PF conducted a flapless approach, touching down gently at approximately 100 kt. Almost immediately after touchdown, the landing gear began to collapse. The PNF immediately shut down the engines and feathered the propellers. The aircraft settled onto the centreline luggage pod and main undercarriage doors, coming to rest after a ground run of approximately 400 m, yawing slightly right. The PF used rudder to keep the aircraft on the paved surface. After stopping, the commander ordered evacuation; the pilots completed the shutdown checklist before vacating. The flight time from electrical failure to landing was about 37 minutes.
Examination
The aircraft was lifted onto a trailer and moved to a hangar. The landing gears partially extended; they were lashed to prevent further damage. Visual inspection showed hydraulic lines intact and no broken landing gear components. The battery, reconnected after the accident, showed 10 V, indicating full discharge. Starter/generators were tested and found fault-free. They were reinstalled, and the electrical system functioned normally during the ferry flight to Denmark for full repair. Additional investigation of the landing gear during repair revealed no fault. The investigation was unable to determine the cause of the electrical failure.
Landing Gear System
The Beech B200 is equipped with an electrically‑powered hydraulic power pack for landing gear operation. Alternate extension is via a hydraulic hand pump. Earlier models use an electrically operated system with a 28 V DC motor and chain drive; OO-LET had the hydraulic system. The manufacturer stated the hand pump system has a relief valve that ports fluid when pressure is exceeded.