What happened
On 19 May 2017, a Piper PA-24-250 Comanche, registration N673SA, was conducting a private flight when it encountered difficult conditions during an approach to Firs Farm Airfield in Berkshire. The aircraft was approaching a grass runway during a period of heavy rainfall. The pilot performed a touchdown with roughly 400 m of the runway remaining, though the approach speed was noted as being higher than ideal.
While attempting to decelerate, the pilot applied heavy braking; however, the wheels began to lock, necessitating a reduction in brake pressure to avoid a skid. This reduction in braking effectiveness significantly increased the required stopping distance. As the aircraft reached the end of the available runway, the pilot attempted a turn to avoid an area planted with crops. During this maneuver, the aircraft skidded and slid off the grass surface. The impact resulted in the collapse of the left landing gear, though both occupants escaped the aircraft without injury.
The investigation
Investigators examined the aircraft's performance capabilities relative to the runway conditions. While manufacturer data suggested a corrected landing distance of 309 m for a wet grass surface using maximum braking techniques, the pilot's need to ease off the brakes due to wheel locking meant the actual distance required was much greater. The investigation also noted that the pilot's touchdown point was late, leaving insufficient margin for the high-speed approach and the degraded braking performance.