History of the Flight
The flight was intended to test the engines after the aircraft's annual maintenance check. The pilot, who also performed maintenance, completed pre-flight checks and functioned the hydraulic system on the ground. After a normal takeoff, the landing gear and flaps were retracted, with all three gear legs indicating up and locked. The pilot flew a large visual circuit to verify engine operation and set up for a long final approach to Elstree. Upon selecting gear down, both main gear legs locked down, but the nose gear green light did not illuminate. Initiating a go-around due to slower traffic, the pilot retracted flaps and selected gear up, noting that the nose gear remained in a semi-retracted state. Troubleshooting included selecting gear down (only main gear locked), using the emergency hand pump (no resistance and smell of hydraulic fluid), and activating the emergency CO2 blow-down bottle (no effect). After circling for about 30 minutes to allow other aircraft to land, the pilot performed a flapless approach, shut down both engines, and feathered propellers. The aircraft touched down on the main gear, but soon the nose sank, and the nose gear retracted, causing the nose to scrape along the runway until the aircraft stopped. The pilot and passenger exited normally.
Recovery of the Aircraft
The recovery plan involved lowering the tail to manually pull the nose gear forward into the locked position. A truck pulled a rope attached to the tail tie-down ring while four people sat on the horizontal tail and the pilot held the brakes. When the tail was low enough, the pilot exited and began pulling the nose gear. As he did so, the main landing gear retracted, causing the aircraft to hit the ground. The truck then pulled off the tie-down ring and surrounding skin.
Landing Gear System Description
The aircraft has a hydraulically actuated retractable tricycle landing gear. The nose gear retracts aft, main gear retracts forward. Each leg has a hydraulic actuator that extends a drag link to an over-centre position for downlock. Microswitches indicate locked position via cockpit lights. The system includes an emergency hand pump and a CO2 blow-down bottle for hydraulic failure. The hydraulic lines of all three actuators are interconnected, so moving one actuator displaces fluid that can move the others.
Maintenance History
The aircraft underwent an annual inspection completed on 1 February 2005, the first flight since then. During inspection, the landing gear was cycled and hydraulic lines checked. Between August 2002 and the accident flight, the aircraft flew only once (45 minutes on 10 May 2004). Total airframe hours were 2,341 hours.
Examination and Findings
An AAIB inspector found no mechanical fault with the main or nose gear. Congealed hydraulic fluid was present around the nose gear door and on the belly aft of the nose gear bay. The nose gear actuator and lines could not be inspected without jacking the aircraft, which was not possible at the time. The loss of hydraulic fluid in flight resulted in insufficient actuating force to lock the nose gear down, as more force is required to extend the nose gear against the slipstream compared to the main gear.