Incident Overview
On 19 July 2020, at approximately 18:25 local time (CEST), a Piper PA-28-181 aircraft, registration LX-AVA, experienced a power loss about one minute after departing from St. Gallen-Altenrhein Airport (LSZR). The aircraft was on a private VFR flight returning to Luxembourg (ELLX) after a day trip. The pilot and one passenger, who also held a valid pilot license, were on board. No injuries occurred, and the aircraft remained undamaged.
Sequence of Events
The preflight checks and engine run-up were performed without anomalies. Takeoff was from runway 28. At about 1550 ft QNH and 250 ft above Lake Constance, the engine began to stutter and power decreased noticeably. The pilot reduced the aircraft to level flight, but airspeed dropped to 68 KIAS. The pilot verified the fuel selector, ignition key, throttle, mixture, electric fuel pump (ON), and carburetor heat (OFF). All engine instruments were within the green range, and no circuit breakers had tripped. The stuttering continued, prompting the pilot to execute a right turn back toward the airport. The passenger radioed that the engine was stuttering and they were turning back. The air traffic controller cleared the aircraft to land on runway 10. The aircraft touched down at 18:27:47 without further incident.
Technical Investigation
The aircraft's last maintenance was a 100-hour/annual inspection on 17 July 2020, which included a compression test with the following results: cylinder #1: 78 PSI, cylinder #2: 76 PSI, cylinder #3: 70 PSI, cylinder #4: 78 PSI. After the incident, a post-flight inspection on 30 July 2020 revealed very low compression on cylinder #3. The piston and rings showed no damage, and the intake and exhaust valves had normal combustion deposits. The cylinder was replaced with a new unit, including valves, piston, and rings; subsequent engine test runs produced the required power.
Probable Cause
The investigation determined that low compression in cylinder #3 caused the power loss.