What happened
On 23 August 2016, a Vans RV-9A, registration G-RPRV, was performing a private flight from Kemble Airfield to Nympsfield Airfield. The pilot had reviewed briefing materials regarding the undulating nature of the Nympsfield grass runway prior to arrival.
During the landing roll on a north-easterly heading, the aircraft was traveling at approximately 20 kt. The pilot noted the presence of a hump in the runway surface and believed they may have instinctively moved the control stick forward while traversing the uneven terrain. Suddenly, the nose landing gear failed, causing the nose of the aircraft to drop abruptly. The propeller struck the ground, and the momentum caused the aircraft to flip onto its back.
The pilot, who sustained minor injuries, managed to turn off the electrical master switch before using a fire axe to cut a hole in the damaged canopy to facilitate an escape.
The investigation
The AAIB examined the aircraft and the landing site. While the surface did not show specific holes or troughs, investigators confirmed that the nose landing 1landing gear leg had bent backward, which significantly reduced the propeller's ground clearance.
Information from the local gliding club indicated that certain areas of the airfield feature steep slopes near the winch track, which are designated as unlandable. However, the investigation established that the aircraft had remained clear of this specific area.
The investigation also reviewed historical data regarding the Vans RV series. The AAIB noted that there have been numerous previous instances of nose landing gear failure in similar aircraft models. The Light Aircraft Association (LAA) is aware of research suggesting that operating on rough ground can induce a harmonic resonance in the nose gear leg, potentially leading to structural failure.
Findings
- The nose landing gear leg failed and bent backward, causing the propeller to strike the ground.
- The aircraft inverted due to the sudden loss of nose gear structural integrity.
- The pilot may have applied forward elevator input while traversing a runway hump, which could have contributed to the loading of the gear.
- The aircraft was operating on an undulating grass surface, a condition known to potentially trigger resonance-related failures in this aircraft type.