What happened
On Saturday, April 6, 2002, at approximately 11:30 local time, a Cessna 152, registration F-GGCS, was conducting a flight training session at the Lyon Bron aerodrome. The aircraft, operated by a local flying club, was occupied by an instructor and a student pilot. Following two takeoff and landing cycles on runway 34, the aircraft reached an altitude of approximately 200 feet during the initial climb when the engine experienced a series of RPM fluctuations accompanied by severe vibrations.
The instructor took control of the aircraft, leveled off, and performed a low-altitude right-hand pattern to approach runway 34. After notifying air traffic control of the engine issues, the crew was granted priority landing. The instructor successfully landed the aircraft and proceeded to the parking area while continuing to use the engine.
The investigation
Post-flight inspection of the Lycoming 0-235-L2C engine revealed that cylinder number 2 had become detached from the crankcase. Investigators found that three mounting studs at the base of the cylinder had fractured. Additionally, the exhaust manifold was severed at the point where it connects to the cylinder.
At the time of the incident, the engine had completed a 50-hour inspection on April 4, 2002, which included a visual check of the cylinder bases in accordance with airworthiness directives. The engine had operated for eight hours since that inspection and had accumulated 602 hours since its last overhaul.
Technical analysis of the fracture surfaces on the recovered studs revealed fatigue cracking, indicating progressive failure due to cyclic loading. No evidence of corrosion or material inclusions was found. Examination of one specific stud showed signs of abnormal bending stress, though investigators noted this could have resulted from either insufficient tightening or the prior failure of other missing studs.