What happened
On July 19, 2020, a Piper PA-28-181, registered as LX-AVA, departed from St. Gallen-Altenrhein Airport (LSZR) for a flight to Luxembourg. The aircraft, carrying a pilot and a licensed passenger, took off from runway 28 at approximately 18:25 local time.
Roughly one minute after takeoff, while at an altitude of approximately 1,550 feet QNH (about 250 feet above the lake), the engine began to sputter, resulting in a noticeable loss of power. The aircraft's airspeed dropped from 85 KIAS to 68 KIAS. The pilot immediately transitioned the aircraft into level flight and performed a rapid assessment of the engine controls, including the fuel selector, ignition, mixture, and carburetor heat. Finding no obvious control issues or electrical failures, the pilot initiated a right-hand turn to return to the airport. The passenger notified air traffic control of the engine sputtering and declared an emergency. The aircraft successfully landed on runway 10 at 18:27, remaining undamaged with no injuries to the occupants.
The investigation
SUST examined the aircraft's maintenance history and technical condition following the incident. A compression test conducted two days prior to the flight, as part of a 100-hour/annual inspection, had shown all cylinders were within acceptable limits, with cylinder number 3 showing only a 10 PSI difference from the others. However, a follow-up inspection on July 30, 2020, revealed that the compression in cylinder number 3 had dropped significantly.
Technical analysis determined that the loss of power was caused by a leak in either the intake or exhaust valve of the third cylinder. Investigators found typical combustion residues on the valves, which can prevent a proper seal.
Findings
- The primary cause of the engine power loss was compression loss in cylinder number 3 due to a leaking intake or exhaust valve.
- The leak was likely caused by carbon deposits or lead particles from Avgas accumulating between the valve face and the valve seat.
- While the compression readings during the previous inspection were within the manufacturer's allowable tolerances, the engine's condition deteriorated rapidly within just a few flight hours.
- The pilot's decision to perform a low-altitude turn to return to the airport, while successful, was noted as a high-risk maneuver that can lead to loss of control.