What happened
On 28 January 2006, a Reims Cessna F152, registration G-BHCP, was conducting a training flight near Meden Vale, Nottinghamshire. Approximately 20 minutes into the flight, the engine began running unevenly with severe vibrations. The instructor attempted to increase power to initiate a climb, but within 10 seconds, the engine RPM dropped and the engine continued to run erratically. After applying carburettor heat, the instructor noted the RPM remained unstable. The instructor then searched for a suitable landing site, transmitted a 'PAN' call, and briefed the student. The aircraft was successfully landed in a field roughly half a mile southeast of Meden Vale. The landing caused damage to the nose landing gear and the lower engine cowling, but the two occupants escaped without injury.
The investigation
An engineering examination of the Lycoming O-235-L2C engine revealed that the No 4 cylinder had completely detached from the engine at the area between the cylinder-to-crankcase mounting flange. Metallurgical analysis showed that external corrosion pits on the outer surface of the cylinder had reduced the wall thickness. These pits acted as stress raisers, leading to the initiation and propagation of a fatigue crack that traveled around approximately 36% of the cylinder's circumference before the final failure.
Investigators also noted a lack of historical maintenance documentation. While the engine had been overhauled in 1997, the original detailed worksheets from that overhaul were unavailable, as the overhaul organisation had destroyed them in accordance with then-current regulations. Furthermore, there were no records available to confirm the specific serial numbers of the cylinders installed during that overhaul.