What happened
On 17 July 1999, a Viking Dragonfly Mk 3, registration G-BKPD, was involved in an incident at Cambridge Airport during a private flight. Following a period of inactivity, the pilot intended to perform a high-power engine run-down on Runway 23 to verify the aircraft's operational status. The weather conditions at the time featured a surface wind of 260 degrees at 12 knots.
During the procedure, the pilot conducted a brief flight over the runway to confirm that the flight controls were functioning correctly. The aircraft subsequently returned to the runway surface at a speed of approximately 55 knots. Upon making contact with the ground, a vibration was detected originating from the forward section of the aircraft. Suspecting an engine-related issue, the pilot shut down the engine; however, the vibration intensified as the aircraft's speed decreased. When the aircraft reached a speed of roughly 25 knots, the nose landing gear collapsed, resulting in damage to the gear assembly. No injuries were reported, and the propeller remained undamaged.
The investigation
The investigation focused on the cause of the vibration and the subsequent structural failure of the nose gear. Investigators examined the condition of the nosewheel pivot and the engine components. It was established that the aircraft had been stationary for an extended period prior to the flight.
Findings
- The investigation determined that engine oil leakage had contaminated the nosewheel pivot.
- This oil contamination reduced the necessary friction within the pivot mechanism.
- The loss of friction led to the onset of nosewheel shimmy, which manifested as the vibration felt by the pilot.
- The mechanical instability caused by the shimmy contributed to the collapse of the nose landing gear.