What happened
On June 11, 2020, a Mooney M20J, registration HB-DFK, was performing a private VFR flight departing from and returning to Grenchen Airport (LSZG). After completing a 30-minute local flight, the pilot was cleared for a direct approach to runway 06.
During the landing phase, the aircraft touched down and subsequently lifted off the runway. This cycle repeated several times, with each subsequent impact becoming increasingly severe. The aircraft eventually sustained damage to its propeller and nose gear. The pilot was uninjured, but the aircraft suffered heavy damage.
The investigation
SUST examined radio communications, webcam footage of the landing, track markings on the runway, and GPS data from the aircraft's collision warning system. The investigation focused on the aircraft's approach speed, the pilot's recent training history, and the specific handling characteristics of the Mooney M20 series.
Analysis of the GPS data revealed that the aircraft was flying significantly faster than recommended. At 50 feet above the ground, the ground speed was approximately 76 knots, which translates to an indicated airspeed of 81 KIAS. This was well above the manufacturer's recommended 71 KIAS for a normal landing and even exceeded the speed required for a maximum performance landing.
Findings
- The primary cause of the accident was the excessive approach speed, which prevented a proper "main wheels first" touchdown and triggered an initial bounce.
- The subsequent sequence of bounces, known as "porpoising," developed into a pilot-induced oscillation (PIO) as the pilot attempted to correct the pitch with the elevator.
- The pilot's recent flight experience was very limited; they had not flown for two years prior to the accident and had only completed a single afternoon of aircraft familiarization on the Mooney M20J.
- The lack of recent training may have contributed to the pilot's failure to initiate a go-around, which would have been the safest way to terminate the oscillation.
- The Mooney M20 series is known to be susceptible to pitch oscillations during taxiing and landing due to its specific landing gear design.