Incident Overview
On 19 July 2020 at 10:41 local time, a Piper PA-28-161 Warrior II, registered as HB-PMF, made a forced landing in a cornfield near Reitnau, Canton Aargau, Switzerland. The aircraft sustained light damage, and neither the pilot nor the passenger was injured.
Aircraft and Pilot
The four-seat aircraft was owned and operated by Fliegerschule Birrfeld AG. It had been modified from its original Lycoming O-320 gasoline engine to a Technify TAE 125-02-99 diesel engine. The pilot, a Swiss national born in 1953, held a Private Pilot Licence (PPL(A)) issued by the Swiss Federal Office of Civil Aviation. He had 648 total flight hours, including 146 hours on the accident aircraft type.
Engine Failure
The flight departed Birrfeld Airfield at 10:27 for a scenic flight over the Alps. At 5,500 ft above sea level in cruise flight with 75% power, the engine failed while over the Zofingen region. The pilot noted that both FADEC indicator lights were flashing. Despite performing the engine failure checklist, the engine could not be restarted.
Forced Landing and Aftermath
During the descent, the pilot initially aimed for Triengen airfield but decided to land in a cornfield near Reitnau, judging that no suitable emergency landing sites were within gliding range to reach Triengen. After touchdown, the aircraft came to a stop against a furrow at the far end of the field. The nose gear collapsed, causing minor damage to the propeller and nose gear. Flight path data from a collision warning device showed a glide toward Triengen, followed by a turn back to the field initiated at about 100 m above ground, with a decreasing turn radius.
Investigation Findings
Examination revealed that the high-pressure fuel pump had a mechanical defect: a broken spring caused the inlet valve to stick in the open position, preventing the pump from maintaining adequate pressure in the common-rail system. FADEC data showed that common-rail pressure dropped from its setpoint of 1063 bar to 9 bar within two seconds. The pump had accumulated 592 hours since new, with a scheduled replacement interval of 600 hours. The engine manufacturer reported that only three such failures had occurred in 6.7 million flight hours, considering the event rate acceptable. A similar engine failure had occurred in 2015 with the same training school's HB-PQI, but that was due to a failed fuel supply pump.