What happened
On July 29, 2007, an experienced pilot was performing a series of aerobatic maneuvers at Ardfert Private Airfield in County Kerry. Having previously completed a successful 18-minute aerial display for the Ardfert Festival, the pilot had landed at the nearby airfield for a brief rest. Upon departing for a return flight to Coonagh Airfield, the pilot began a sequence of maneuvers, including horizontal rolls and an inverted fly-past. During the final maneuver—a climbing roll to the right—the engine of the Steen Skybolt, registration EI-CIZ, suddenly sputtered and ceased operation.
As the aircraft lost altitude rapidly, the pilot attempted to level the wings. The aircraft struck the ground in a nose-down attitude before rebounding into a stone boundary wall covered in hedges. The impact destroyed the aircraft. The pilot, seated in the rear cockpit, sustained fatal injuries.
The investigation
The AAIU examined the wreckage and the engine components at their facility in Gormanston. The investigation focused on the fuel system, the engine's mechanical state, and the aircraft's flight history. Technical analysis of the engine revealed no mechanical defects that would have caused a failure, though it was noted that the engine had been in service for 27 years without a full overhaul.
Investigators scrutinized the design of the main fuel tank, which was divided into two sections. The cockpit gauge only monitored the upper section of the tank. The investigation also examined the 'flop tube'—a flexible hose with a weighted end designed to ensure fuel delivery during inverted flight. Data from the aircraft's GPS and witness accounts helped reconstruct the flight path and the sequence of the engine's failure.
Findings
- The primary cause of the accident was engine fuel starvation occurring during the climbing roll.
- The pilot was performing aerobatic maneuvers while the upper section of the main fuel tank was empty, meaning the cockpit gauge read zero.
- During the steep climbing roll, the movement of the aircraft caused the weighted end of the flop tube to uncover, cutting off the fuel supply to the engine.
- The low altitude at which the engine failed left the pilot with insufficient height to recover the aircraft or attempt an engine restart.
- While the aircraft still contained significant fuel in the lower section of the tank, the specific configuration of the fuel intake prevented it from reaching the engine during that specific maneuver.