What happened
On March 9, 2012, a Tecnam P2002-JF, registration HB-KPG, was conducting a daytime VFR instructional flight at Geneva Airport (LSGG). The flight crew, consisting of a flight instructor and a student pilot, prepared for a session involving circuit training and a solo navigation flight. After performing standard pre-flight checks and refueling with 25 liters of AVGAS UL91, the aircraft taxied to the grass runway 05 holding point.
The aircraft remained at the holding point for approximately 20 minutes to allow for engine warm-up and GPS programming. During this period, the engine operated normally at 1100 RPM. Upon receiving takeoff clearance, the student pilot applied full power. However, shortly after takeoff, the engine suffered a significant loss of power, with propeller RPM dropping from 2000 to 1500, accompanied by intense vibrations.
The instructor took control of the aircraft. Due to the insufficient altitude and power, the instructor opted to fly along the edge of a nearby forest rather than attempting an immediate landing on the grass runway. The aircraft struggled to climb, maintaining an altitude of approximately 1700 ft AMSL. After communicating the engine difficulties to the tower controller, the instructor requested an emergency landing on the paved runway 23. The aircraft landed safely on the concrete runway, and the vibrations ceased once power was reduced for landing.
The investigation
SESA examined the technical and operational aspects of the incident. Investigators reviewed maintenance records, which showed a 100-hour inspection had been completed in December 2011, including carburetor servicing and spark plug replacement. The investigation also looked into previous instances of engine fluctuations observed in similar Tecnam aircraft at the same aero club, which had been attributed to the use of automotive gasoline (SP98) before the club switched to AVGAS UL91.
Technical analysis of the engine components revealed that the spark plug for cylinder number 2 showed signs of contamination by small beads on the electrode and ceramic insulator. This finding suggested that the cylinder had experienced excessively high operating temperatures. However, subsequent engine tests on a test bench were unable to replicate the power loss, and no mechanical defects were found in the cylinder head.
Findings
- The primary cause of the incident was a loss of engine power following takeoff.
- The investigation could not definitively determine the exact origin of the power loss, though a temporary overheating of cylinder number 2 was a strong possibility. The asymmetric airflow during the 20-minute warm-up period, combined with the propeller wash, may have caused insufficient cooling for that specific cylinder, potentially leading to pre-ignition.
- There was a secondary hypothesis regarding carburetor icing, though meteorological data showed a relatively low dew point, making the risk of icing less likely than overheating.
- The instructor's decision to land on the paved runway 23 was deemed appropriate given the altitude and remaining power.
- The air traffic controller reacted promptly and appropriately by clearing the necessary airspace to facilitate the emergency landing.