What happened
On the evening of November 18, 1999, a Piper PA-46 Malibu, registration HB-PLD, was conducting an IFR flight from Lyon-Bron to Grenchen with two passengers on board. During the approach to Grenchen, the pilot was notified of heavy snowfall and an unplowed runway. After performing a missed approach, the aircraft diverted to Bern-Belp, where weather conditions were also deteriorating.
At the time, airport services had suspended snow removal operations because heavy snowfall was immediately covering cleared areas. Although the runway was officially closed due to snow, the pilot was permitted to land at his own risk following the precedent of another aircraft. During the ILS approach to runway 14, the pilot experienced severely obscured visibility through the windscreen due to snow accumulation. The aircraft touched down on the left side of the runway, and as it rolled, it drifted off the left edge of the pavement. The sudden deceleration caused the nose gear to collapse, resulting in damage to the nose gear, propeller, engine mounts, and the engine. A runway sign was also damaged in the excursion.
The investigation
The investigation examined the aircraft's technical state, the weather conditions, and the pilot's decision-making process. Investigators confirmed the aircraft was within weight and balance limits and was certified for IFR Category I operations. The pilot held a valid license and had sufficient fuel reserves.
Technical inspections revealed that while electrical de-icing elements were active, the pneumatic leading-edge boots had not been deployed after leaving the holding pattern, as no ice buildup was initially visible. However, hard-packed snow was found on the leading edges following the accident. The investigation also noted that the pilot's visibility was significantly compromised by snow accumulation on the windscreen and the effects of the heated window panel.
Findings
- The primary cause of the runway excursion was the loss of directional control while landing on a snow-covered runway during heavy snowfall and low visibility.
- The pilot's visibility was severely restricted by snow accumulation on the windscreen.
- The lack of visual contrast between the snow-covered runway and the surrounding environment led the pilot to focus on the left edge lights, causing the aircraft to land near the runway boundary.
- The uneven snow depth on the runway surface caused the aircraft to lose directional stability during the rollout.
- Potential aerodynamic disturbances caused by snow accumulation on the wing leading edges may have further destabilized the aircraft during touchdown.