What happened
On 4 April 2003, a Rutan Varieze, registration G-BEZE, was conducting a flight at Biggin Hill Airport to evaluate the performance of a recently installed, overhauled engine. The flight was part of the procedures required to renew the aircraft's Permit to Fly. The pilot's plan involved completing two circuits, including one go-around, before performing a full-stop landing.
Prior to departure, the aircraft was in its usual parked position with the nose gear retracted. To prepare for flight, the pilot raised the front of the aircraft and operated the cockpit handle to extend the nose landing gear. The pilot noted that the landing gear warning light had extinguished and the handle was stowed, leading to the belief that the gear was securely locked. During the flight, the pilot did not adjust the gear handle, as there was no intention to retract the gear after takeoff.
After completing the first circuit and a subsequent go-around, the pilot performed a normal approach using the airbrake. Upon touchdown, the nose landing gear collapsed. The aircraft proceeded down the runway on its nose bumper until it came to a halt. The pilot was uninjured.
The investigation
Investigators examined the nose landing gear mechanism of G-BEZE and discovered significant damage to the worm gear and crown wheel. Specifically, the teeth on the crown wheel had been stripped across approximately 120 degrees of its circumference. This damage indicated that the gear had been subjected to an unusually high load.
Technical analysis focused on the locking mechanism of the nose gear. The system relies on the actuating arms moving to an over-centre position to lock the gear in place. If the gear is not over-centre, the weight of the aircraft is supported solely by the mesh of the gear teeth between the worm gear and the crown wheel. While the warning system was tested and found to be functional, the investigation looked into whether the gear had been properly locked prior to takeoff.
Findings
- The investigation established that the crown wheel teeth failure was the primary reason the gear could not support the landing loads.
- It is probable that the nose landing gear was not in the fully over-centre locked position during the flight, despite the cockpit warning light extinguishing.
- While the gear teeth could withstand the loads experienced during taxiing, they were unable to sustain the much higher loads encountered during the landing phase.
- Because the gear was not mechanically locked, the mechanism retracted upon impact, causing the collapse.