Incident Overview
On 2 September 2021, at 14:55 local time, a Robin DR40 (registration HB-KLT) operated by the Air-Club d'Yverdon-les-Bains was conducting a solo navigation flight as part of the pilot's training for a Private Pilot Licence (PPL(A)). The flight originated from Bressaucourt aerodrome (LSZQ) and was destined for Yverdon-les-Bains aerodrome (LSGY). The pilot, a Swiss national born in 1946, had accumulated 240 hours and 36 minutes of total flight time, with 14 hours and 8 minutes in the preceding 90 days, and a total of 795 landings, 35 of which occurred in the last 90 days. The flight was conducted under Visual Flight Rules (VFR).
Sequence of Events
After completing the first two legs with landings at Sion (LSGS) and Bressaucourt (LSZQ), the pilot proceeded to Yverdon for the final landing on runway 05. The aircraft touched down on the paved runway in a three-point attitude but briefly became airborne again. The pilot was unable to stabilize the aircraft's attitude, and the aircraft bounced three times before departing the runway. At that point, the pilot regained control and taxied via taxiway Bravo to the apron. The nose gear and propeller tips sustained minor damage; the pilot was uninjured.
Findings
According to the pilot's statements, no technical malfunctions played a role in the serious incident. Visual meteorological conditions prevailed at the time.
Analysis
The investigation identified parallels with three previous occurrences involving aircraft HB-TDD (13 October 2017), HB-CCD (5 July 2017), and HB-DFK (11 June 2020). The common element is that after an initial landing and subsequent takeoff (bounce), a porpoising motion can develop. This results from an increase in the angle of attack caused by the nose gear rebounding on landing, followed by a reduction in angle of attack as the pilot pushes forward on the elevator control. The repeated pilot inputs on the elevator create a pilot-induced oscillation, which can be safely terminated by initiating a go-around.