What happened
On May 28, 2003, a Piper PA-28-151, registration HB-OQK, departed Birrfeld as part of a group excursion to Italy. The flight was intended to proceed via Willisau and the Simplon Pass, with a planned stop in Parma. However, due to deteriorating weather conditions and the need to avoid a restricted zone caused by artillery practice near the Simplon Pass, the pilot selected a different route.
While flying through the Napf region, the aircraft encountered significantly degraded visibility. At approximately 12:08, while maneuvering in a right-hand turn, the aircraft struck trees on the ridge of the Bärhegechnübeli near Sumiswald. The impact caused the aircraft to crash into the mountainside. The two fatalities on board were confirmed at the scene by emergency responders.
The investigation
Investigators from the SUST examined radar plots, GPS data from the onboard Garmin unit, and flight plan records to reconstruct the aircraft's path. The investigation focused on the pilot's navigation decisions and the prevailing meteorological conditions. Evidence showed that the pilot had adjusted the route to avoid terrain and weather obstacles, but the chosen path crossed areas where the GAFOR weather forecast indicated that VFR routes were closed.
Technical inspections of the Piper PA-28-151 revealed no mechanical failures or engine issues prior to the impact. The aircraft's weight and balance were within limits, and the engine was heard to be operating normally until the collision. The investigation also noted that the pilot was attempting to avoid rising clouds by initiating a turn, but the maneuver was executed too late.
Findings
- The primary cause of the accident was the continuation of VFR flight under instrument meteorological conditions (IMC).
- The aircraft encountered a closed cloud layer that obscured the terrain.
- The pilot's attempt to avoid encroaching clouds via a right-hand turn was initiated too late, leading to a collision with trees and the terrain.
- The chosen flight path intersected areas where weather minima for VFR flight were not met.