Incident Overview
During an IFR approach to Grenchen Airport's runway 25, the pilot of a single-engine aircraft (type unspecified) deviated from the published procedure. After passing over the Alps and a layer of stratus over the Plateau, the pilot reached the Willisau VOR and was cleared to begin the approach. He performed a standard turn but subsequently followed the 290° radial instead of the published 280° radial.
Sequence of Events
As the aircraft progressed along the incorrect radial, the DME system indicated 7 NM from the VOR. At that point, the pilot realized he was too far from the normal approach track. He disengaged the automatic pilot system and attempted to gain altitude. With the flaps and landing gear extended, the aircraft could not achieve sufficient climb height.
Collision and Aftermath
The aircraft struck the wooded slope of Mt Balmfluechöpfli, elevation 1,289 meters, located approximately 12 km northeast of Grenchen Airport. Visibility was poor due to thick fog. On impact, the aircraft disintegrated. The pilot was killed. The female passenger, who was seated in a seat facing opposite the direction of flight, sustained minor injuries and was able to walk from the wreckage to seek help.
Probable Cause
The official investigation identified the following factors: selection of radial 290° instead of the published 280° radial; inappropriate NAV setting; too late and inconsistent throttle reset; difficult IFR approach procedure without radar monitoring; and too high speed on approach.