What happened
On June 26, 2003, at approximately 11:55 UTC, a Cessna 152, registration CS-AYG, departed from Cascais Municipal Aerodrome (LPCS) for a solo navigation training flight. The flight plan involved a route through Santarém (LPSR) and Santa Cruz (LPSC) before returning to Cascais.
Shortly after takeoff, while climbing through 700 feet, the pilot experienced a sudden reduction in engine RPM accompanied by heavy vibrations throughout the airframe. The pilot immediately applied full power, enriched the mixture, and set the carburetor heat to maximum cold; however, the engine RPM remained stuck between 60/650 RPM.
Following established procedures, the pilot executed a tight circuit to return to the airfield. During the approach to runway 35, another pilot observed smoke trailing from the aircraft, prompting the pilot to declare an emergency. The pilot successfully landed the aircraft without injury. While no fire occurred, oil from the engine's breather had leaked along the left side of the fuselage, which caused the visual illusion of smoke.
The investigation
The GPIAAF investigation focused on the engine's condition and maintenance records. Post-incident inspections of the Textron Lycoming O-235-L2C engine revealed significant damage to cylinder #2, including fractured piston rings and a fractured piston head. The investigation also examined the engine's service history, noting it had been overhauled and reinstalled on May 28, 2003.
Investigators reviewed the Aircraft Technical Reports and found that while high oil temperatures and lower-than-normal RPMs were known to the crew, these anomalies were only communicated orally and not recorded in writing. Furthermore, the investigation found that the engine had been serviced with Aeroshell 100 oil, which is a dispersive oil not recommended by the manufacturer for the initial 50-hour "break-in" period of a newly overhauled engine.
Findings
- The primary cause of the power loss was the fracture of the piston rings and piston head in cylinder #2 due to engine detonation.
- The use of a dispersive oil type during the critical engine break-in period contributed to the detonation phenomenon.
- Failure to follow recommended manufacturer break-in procedures allowed the engine to operate at excessively high temperatures.
- Inadequate maintenance logging meant that high oil temperatures and excessive oil consumption were not formally documented, preventing maintenance personnel from taking corrective action.
- A lack of adherence to internal reporting standards allowed known engine anomalies to remain unaddressed.