History of the Flight
After departing Biggin Hill Airport, the pilot performed the normal after-takeoff checks, including selecting the landing gear up. Air Traffic Control then informed the pilot that the landing gear appeared still extended. The pilot observed the gear selector handle in the UP position with the red 'Gear Unsafe' light illuminated. A visual check confirmed the main gear legs were down. The pilot selected the gear down to recycle it but subsequently could not select it up. Suspecting the nose gear might not be locked down, he returned to the airfield. A fly-past confirmed all three legs appeared down, and the pilot decided to land. During the landing roll, the aircraft veered left and stopped as the landing gear collapsed. The pilot shut down the engines, switched off the electrical master, and activated the fuel firewall shut-off valves before evacuating with the other occupants.
Landing Gear System
The tricycle landing gear is powered by an electric motor and gearbox assembly. Mechanical down-locks are provided by notched hooks and plates on the main gear drag braces and an over-centre action on the nose gear drag brace. The motor has separate fields for UP and DOWN directions, controlled by a relay box. Limit micro-switches activated by cams on the gearbox stop the motor via dynamic braking. A 5 amp circuit breaker supplies power to the control relays, while a 60 amp circuit breaker feeds the motor. A squat switch on the right main gear prevents inadvertent UP selection on the ground, and a spring-loaded latch covers the selector handle when down on the ground.
Post-Accident Examination
Examination revealed all three landing gear legs had collapsed. The nose gear remained sufficiently extended to keep the propellers clear of the ground, while the main gear had almost fully retracted, causing severe abrasive damage to the rear fuselage underside, flaps, and nacelles. The main gear actuator attachment fittings had failed under the aircraft's weight, indicating the gear was not locked at touchdown or became unlocked during the roll. The 60 amp motor circuit breaker was tripped; the 5 amp control circuit breaker was not. The landing gear selector was found in the DOWN position. The emergency extension mechanism moved freely but could not wind the gear down due to damage; the gear had to be pulled down manually.
Discussion
The investigation suggested an electrical problem prevented the gear from fully retracting after the downlocks had unlocked. The gear movement was small enough that the pilot and ground observers believed it was fully down. The 'Gear Unsafe' red light and absence of three green lights indicated otherwise. The correct procedure—selecting gear down, checking for three greens, isolating the landing gear circuit breaker if necessary, and using the emergency extension mechanism—was not followed by the pilot. The tripped 60 amp circuit breaker indicated the motor may have tried to complete the extension cycle against the weight of the aircraft on unlocked legs after touchdown. Due to ongoing structural repairs, the landing gear system could not be tested electrically at the time of the report.