What happened
On February 7, 2020, a Piper PA-18, registration HB-POG, was performing a mountain landing training flight at the Rarogne airfield in Switzerland. During the takeoff roll on runway 28, the aircraft climbed to an altitude of approximately 40 meters when the engine experienced a progressive and complete loss of power.
As the aircraft was positioned near buildings at the end of the runway, the instructor in the rear seat took control to execute an emergency maneuver. The instructor performed a 90-degree left turn to avoid obstacles, leading to an emergency touchdown on the grass adjacent to the threshold of runway 10. The aircraft continued toward a nearby forest, and while a collision with trees was unavoidable, the instructor managed to guide the plane between two large trunks. The impact tore both wings from the fuselage, bringing the aircraft to a halt. Despite a significant fuel leak, no fire occurred, and both occupants were able to exit the wreckage uninjured.
The investigation
Investigators examined the wreckage and the engine's performance. The investigation found that the Quick Drain Valve on the carburetor bowl was in the open position. Evidence of fuel leakage was found on the ground near the aircraft's hangar and on the left side of the fuselage.
Technical tests were conducted on the engine. While the engine functioned normally during bench tests with the valve closed, tests on a similar aircraft revealed that running the engine with the drain valve open caused significant RPM fluctuations and power drops. The investigation also ruled out carburetor icing due to the prevailing atmospheric conditions and confirmed that the fuel selector was correctly positioned.
Findings
- The primary cause of the accident was a loss of engine power during the takeoff phase.
- The loss of power was likely caused by fuel leakage through the Quick Drain Valve, which had been left in the open position following the pre-flight inspection.
- The instructor's decisive actions in maneuvering the aircraft between trees prevented a much more serious outcome.