Incident Overview
On 17 April 2003, at approximately 1115 hours UTC, a DH82A Tiger Moth (registration G-ANHK) was cruising at about 2,000 feet when the pilot noticed a slight engine vibration. Within a few seconds, the vibration worsened and the engine lost power. A backfire was heard, and the pilot observed smoke emanating from the carburettor air intake. Opening the throttle increased the vibration.
Pilot Actions
The pilot checked both magnetos and the fuel supply, finding no anomalies. He then conducted a forced landing into wind. During the landing roll, the aircraft tipped onto its nose, coming to rest on the propeller and left wing tip. The pilot, who was uninjured, climbed out of the open cockpit. There was no fire.
Damage
The aircraft sustained damage to the propeller, engine cowling, cockpit floor, and left wing tips.
Engine Examination
Examination of the engine by a maintenance organisation revealed that the No 2 cylinder inlet rocker arm had failed close to the exhaust valve. The separated portion had become jammed in the exhaust guide. The broken pieces were sent to the AAIB for metallurgical examination, which identified a high cycle fatigue failure that had initiated in a region of mechanical damage.
Aircraft and Engine History
The aircraft had been operated by the current owner for approximately 30 years with low utilisation. The engine had completed 670 hours since overhaul, but only 170 hours since 1978. The last maintenance entry in the log book that would have involved removal of the cylinders and rocker arm was in 1990. It was not possible to determine when or how the damage to the rocker arm occurred.