What happened
On 6 September 2017, a Piper PA-31, registration N250AC, was conducting a private flight from a grass airstrip in Cheshire toward Dublin. Approximately 20 minutes after departure, the pilot contacted London Information to report difficulties with pitch control and announced an intention to divert to Caernarfon Airport.
Radar data and eyewitness accounts indicate that the aircraft approached Runway 25 at a high rate of descent and excessive speed. The aircraft struck the runway with its landing gear and flaps still retracted, performing no discernible flare maneuver. The impact was followed by a significant post-crash fire that destroyed the aircraft. The pilot sustained one fatality.
The investigation
The AAIB examination of the wreckage was hampered by fire damage, but investigators found that the elevator trim was positioned in a way that suggested significant nose-down input. While the aircraft's control surfaces were inspected, the intense heat made a full assessment difficult.
Investigators also examined the aircraft's systems, noting that while the autopilot and flight controls were inspected, the extreme fire damage limited the ability to determine the exact cause of the trim position. The investigation also looked into the pilot's procedures and the aircraft's maintenance history, noting that the aircraft had been subject to standard maintenance routines prior to the flight.
The findings
The investigation focused on the possibility of a trim runaway or an uncommanded movement of the elevator trim. The investigation found that the aircraft's elevator trim was in a position that would contribute to a nose-down pitch. The investigation also noted that the aircraft's electrical systems were subject to significant damage from the fire, which could have affected the trim motor's operation.
Although the exact cause of the trim movement could not be definitively determined due to the fire damage, the evidence suggests that the aircraft was in a configuration that made maintaining level flight extremely difficult. The investigation also noted that the aircraft was flying at a high speed, which would have increased the physical force required to counteract the nose-down trim.