What happened
On 13 June 1998, a Montgimterie-Bensen B8MR gyroplane, registration G-WHIR, was conducting a private flight near Stornoway Airport. After performing several practice maneuvers and touch-and-go landings, the pilot transitioned to visual flight rules (VFR) flying toward the north.
As the aircraft approached the village of Coll, witnesses observed the pilot performing low-altitude maneuvers, including a brief hover over a road. During this phase, the pilot appeared to be leaning heavily to one side. The flight ended abruptly when the engine noise increased and the aircraft entered a steep climb at low speed. The gyroplane then began to slide backward and roll to the left, eventually turning upside down. During this sequence, the rotor blades struck the propeller, causing the propeller to break apart and the aircraft to impact the ground in a garden.
The investigation
The AAIB investigation focused on the mechanical state of the aircraft and the fuel system. Examination of the wreckage revealed that the transparent PVC sight-tube used to monitor fuel levels had disconnected from the lower fuel tank outlet pipe. This disconnection was caused by the PVC material shrinking and becoming brittle due to prolonged exposure to fuel.
Investigators found that the shrinkage of the tube had created axial tension, eventually pulling the tube off its connection. While the fuel level could not drop below the outlet pipe, leaving approximately 9 litres of usable fuel, the leak was located near the hot engine exhaust. The investigation also noted that a previous ground accident involving damage to the rotor and propeller had not been formally recorded in the aircraft logbooks.
Findings
- The fatal accident was caused by the disconnection of the fuel tank sight-tube, which led to a fuel leak near the hot exhaust.
- The PVC tubing had lost its plasticizer due to fuel contact, causing it to shrink, harden, and eventually pull away from its fitting.
- The pilot may have been distracted by the sight of leaking fuel while attempting to use the ground for a visual reference during a hover.
- The resulting loss of rotor speed and subsequent aircraft attitude led to the rotor blades striking the propeller.