What happened
On September 2, 2021, a student pilot was conducting a solo navigation flight as part of their training for a Private Pilot License. The flight originated from Bressaucourt (LSZQ) and included intermediate stops at Sion (LSGS) before heading toward the final destination of Yver/verdon-les-Bains (LSGY).
Upon approaching runway 05 at Yverdon-les-Bains, the pilot executed a three-point landing. However, the aircraft briefly lifted off the runway again immediately after the initial contact. The pilot was unable to stabilize the aircraft's attitude, leading to a series of three bounces. During this sequence, the Robin DR40, registration HB-KLT, veered off the runway. The pilot eventually regained control and taxied the aircraft via taxiway Bravo to the tarmac. The pilot remained uninjured, though the aircraft sustained minor damage to the nose gear and propeller tips.
The investigation
The investigation established that the flight was conducted under Visual Flight Rules (VFR) in good weather conditions. The pilot reported that no mechanical or technical failures contributed to the incident. Investigators focused on the aerodynamic behavior of the aircraft during the landing phase, specifically looking at the sequence of the bounces.
Findings
- The primary cause of the excursion was porpoising, an oscillatory motion triggered by the initial bounce.
- The phenomenon was driven by a cycle of increasing and decreasing the angle of attack: the nose gear contact increased the angle of attack, while the pilot's subsequent elevator inputs to correct the pitch decreased it.
- The investigation noted that the pilot's repeated elevator corrections contributed to a pilot-induced oscillation.
- The analysis highlighted that such oscillations are most safely interrupted by performing a go-around (missed approach) rather than attempting to correct the pitch through aggressive elevator use.