What happened
On 30 June 2001, a Piper PA-28-161 Cherokee Warrior II, registration G-MAND, was conducting a private training flight at Wolverhampton Airport. The flight was intended to assist in the revalidation of a second pilot's Private Pilot's Licence. Shortly after departing from Runway 28, the engine began to run roughly at approximately 700 feet. The instructor pilot took control as engine speed dropped significantly from full power.
After the engine lost nearly all power output, the instructor decided to perform a forced landing on the reciprocal runway, Runway 10. Despite attempting a sideslip to manage the descent, a strong tailwind prevented the aircraft from touching down until the middle of the runway. The aircraft could not stop within the remaining paved surface, overrunning the runway, passing through a boundary hedge, and coming to rest in a nearby field. During the excursion, all three landing gear legs failed and the left wing detached from the airframe. The two crew members sustained minor whiplash injuries but were able to evacuate the aircraft safely.
The investigation
The AAIB conducted a detailed examination of the engine and the aircraft components. Investigators focused on the Lycoming O-302-D3G engine, which had been in service for 1,865 hours since its last rebuild. The investigation included a strip examination of the engine, testing of the magnetos, carburettor, and fuel pump, as well as metallurgical analysis of the cylinder assembly.
Engine examination revealed severe wear on the valve operating mechanism, specifically involving the camshaft lobes and follower bodies for the No 3 and No 4 inlet valves. Additionally, the investigation identified extensive cracking within the No 1 cylinder assembly. The cracks were found to have penetrated the full thickness of the cylinder head wall, effectively separating the head from the cylinder.
Findings
- The primary cause of the power loss was a substantial pre-existing crack in the No 1 cylinder head that rapidly extended around the circumference of the head, causing the cylinder to vent.
- While severe wear was present in the valve operating mechanism due to insufficient lubrication, this was not a contributing factor to the immediate engine failure.
- The use of a specific oil additive, which was mandated for other similar engine models but not required for this specific model, might have reduced the observed wear on the camshaft.
- The extent of the cylinder head cracking was significant, and while the exact cause of the initial crack (such as detonation or thermal shock) could not be confirmed, the failure led to the total loss of engine power.