History of the Flight
The pilot, holding a Private Pilot's Licence, planned a flight to Caernarfon with a passenger. After de-icing the aircraft and refuelling, the start-up, taxi, and power checks were uneventful, with all instruments, including the ammeter, indicating normally. The takeoff was normal and the landing gear was retracted. Shortly after departure, the pilot noticed that the electronic horizontal situation indicator (HSI) had failed. He recycled the avionics master switch, and the HSI recovered briefly before failing again. He then observed that the red low-voltage light was illuminated and the ammeter indicated that the battery was not charging. The pilot switched off non-essential electrical items and informed Tatenhill Air Traffic Control (ATC) that he had an electrical problem and would return.
The aircraft joined a downwind leg for Runway 26. All avionics except the HSI were working normally. The pilot reduced airspeed below the landing gear limiting speed and selected the landing gear down. He heard a 'clunk' as the gear appeared to lower; at the same time, all avionics and electrical gauges and indicators failed. The pilot recycled the avionics master switch but could not restore electrical power. The green landing gear down indicator light was not illuminated. With no radios, he could not request a visual inspection from ATC. The pilot then moved the landing gear electrical selector switch to the centre position, in accordance with the emergency gear lowering instructions, and attempted to lower the gear using the emergency system. He operated the locking release system but found the emergency extension lever would not move; it already appeared to be in a fully forward position. The pilot interpreted this to indicate that the landing gear was fully down.
The pilot flew the aircraft low and slow along the runway, hoping ATC would signal a steady green light, but received no acknowledgement. He continued with a low-level circuit, believing the gear was down, and briefed his passenger on the possibility of a gear collapse. The aircraft touchdown was normal, but shortly afterwards the landing gear collapsed. The aircraft travelled on its lower fuselage for about 100 metres before sliding off the left edge of the runway, destroying a runway edge light. It came to rest on soft ground a few metres south of the runway. The pilot and passenger vacated the aircraft uninjured. Eyewitnesses confirmed that the landing gear appeared to be down prior to the accident.
Emergency Landing Gear Lowering
The emergency lowering procedure for the landing gear requires three actions: move the landing gear electrical selector switch to the centre position; position the electrical release arm fully forward; and operate the emergency extension handle. The electrical selector is moved to a neutral position to prevent the motor from opposing the manual lowering. The electrical release arm disconnects the electric motor from the gear operating mechanism; if not fully disengaged, manual lowering is impossible. The emergency extension lever is permanently connected to the landing gear operating mechanism and moves with the gear. It has a telescopic handle that is extended to manually lower the gear. The pilot cannot move this lever until the electrical motor is disengaged by the release arm.
Aircraft Examination
A maintenance engineer examined the aircraft immediately after the accident and found that the alternator circuit breaker had tripped. This circuit breaker is positioned out of the pilot's normal field of view in flight. With the alternator breaker tripped, the aircraft electrical systems were powered solely by the battery. The engineer checked the battery voltage and considered it effectively flat. Later, an AAIB engineering inspector found that the rear mounting of the bracket holding the gear lowering jack had been pulled out of the structure. This failure could only occur if the electrical motor release arm had still been engaged when the aircraft touched down with the gear unlocked. The release arm operated satisfactorily, but it had to be moved fully forward to disconnect the motor from the gear operating mechanism.
Analysis
The aircraft experienced an electrical problem that caused the alternator circuit breaker to trip, leaving the battery to supply electrical loads. When the pilot completed the landing checks, only sufficient battery power remained to partially lower the gear. Without electrical power, the gear indication lights were inoperative. Damage to the aircraft indicated that the electrical motor was still attached to the gear operating mechanism when the landing gear collapsed. It appears likely that during the emergency lowering procedure, the electrical motor release arm was not moved far enough forward to fully disengage the motor from the gear mechanism. Consequently, the pilot could not move the emergency extension lever fully forward, and the landing gear was not down and locked. It collapsed during the landing roll.