What happened
On 17 April 2003, a DH82A Tiger Moth, registration G-ANHK, was conducting a private flight at an altitude of roughly 2,000 feet when the pilot detected a minor engine vibration. This vibration intensified rapidly, resulting in a complete loss of engine power. During the event, the pilot observed smoke emerging from the carburettor air intake and heard a backfire. Attempts to rectify the issue by adjusting the throttle, checking the fuel supply, and inspecting the magnetos yielded no results.
In response to the power loss, the pilot performed a forced landing into the wind at Bromsgrove Farm, near Pewsey, Wiltshire. During the aircraft's landing roll, the plane tipped forward onto its nose, coming to rest on the propeller and the left wing tip. The pilot sustained no injuries and was able to exit the cockpit safely. The aircraft sustained damage to the propeller, engine cowling, cockpit floor, and left wing tips, but no fire occurred.
The investigation
The AAIB investigation relied on the pilot's accident report, telephone interviews, and a metallurgical analysis of a failed engine component. Technical examination of the engine by a maintenance firm identified that the inlet rocker arm of the No 2 cylinder had failed near the exhaust valve. The broken segment of the arm had subsequently become lodged in the exhaust guide.
Records indicated that the aircraft had been owned by the current operator for three decades with infrequent use. While the engine had recorded 670 hours since its last overhaul, only 170 of those hours had been flown since 1978. Notably, the last maintenance entry requiring the removal of the cylinders—and therefore the rocker arm—was dated 1978. Investigators were unable to establish the exact timing or cause of the initial mechanical damage to the arm.