What happened
On June 26, 1997, a Piper PA-18-150, registration D-ENPO, was conducting a VFR cross-country flight from Tallinn to Turku, with a subsequent leg toward Vaasa. While flying near Närpiö, approximately 60 km from Vaasa Airport, the pilot experienced engine roughness and a drop in RPM of 100–200 r/min, accompanied by an increase in exhaust gas temperature (EGT).
To investigate the cause of the engine malfunction, the pilot decided to land in a nearby 1,000-meter-long field. The aircraft touched down on the final quarter of the field at a high speed, causing several bounces. Fearing the aircraft would not stop before reaching a ditch and a road at the end of the field, the pilot applied heavy braking. This caused the aircraft to nose over and eventually capsize upside down. The pilot sustained a minor injury to the right leg, while the passenger was uninjured.
The investigation
The investigation examined the engine components, the aircraft's weight and balance, and the landing sequence. Technicians inspected the engine cylinders, spark plugs, and the carburetor. The investigation also reviewed the aircraft's mass at takeoff, noting it was approximately 28 kg over the maximum allowable takeoff weight.
Findings
- The engine malfunction was caused by combustion irregularities in cylinder number 4, likely resulting from either a spark plug failure or a valve sticking.
- The aircraft was operating at an overweight condition, exceeding the maximum takeoff mass by 28 kg.
- The landing was characterized by excessive speed and multiple bounces on the field surface.
- The primary cause of the accident was the pilot's decision to apply heavy braking during the landing roll, which led to the aircraft'n nose-over and subsequent capsize.