What happened
On July 15, 1990, a private flight was conducted using a SOCATA TB10 aircraft, registered as HB-KAX, departing from Kägiswil airfield. The pilot, accompanied by three passengers including his father-in-law and his parents-in-law, intended to perform a scenic tour over the Bernese Alps. The aircraft took off from Runway 03 at approximately 10:10 local time. Due to noise abatement procedures in effect at the time, the standard departure route required a right-hand turn rather than the usual left-hand pattern.
Witnesses observed the aircraft climbing poorly and flying in a nose-up attitude immediately after takeoff. The plane turned right over the Sibeneich ridge near Kerns. Conditions were hazy with visibility around 5 km. Instead of heading south toward the Brünig Pass as typically planned for such routes, the aircraft appeared to follow the contour of the terrain on its left side at a low altitude. It entered the Kleines Melchtal valley and flew southward.
Approximately nine minutes after departure, near the area known as Chrummelbach, witnesses saw the aircraft exhibiting rolling movements before colliding with trees. The impact occurred in a forested area at an elevation of 1500 meters above sea level. The aircraft was destroyed upon impact. Two passengers were killed instantly. The pilot and one other passenger sustained severe injuries; the pilot later died from his wounds five months after the accident.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the flight path, weather conditions, and aircraft status. The investigation noted that the departure route change to a right-hand turn was unusual for the pilot, who was otherwise familiar with the area. This unfamiliarity complicated navigation. The haze obscured forward visibility, forcing the pilot to rely on visual references from the terrain on his left.
The aircraft's gyroscopic compass had been removed, leaving only the magnetic compass which was destroyed in the crash. The investigation determined that the absence of the gyrocompass prevented the pilot from immediately detecting a course deviation of approximately 20 degrees between the intended route and the actual path. The poor climb performance, measured at 1.91 m/sec compared to the expected 2.43 m/sec, may have been due to downdrafts or suboptimal speed control.
Findings
The primary cause of the accident was the pilot flying too low into a narrow valley. Contributing factors included:
- Navigation error: The pilot likely intended to fly over the Brünig Pass but, disoriented by the unusual right-hand departure and haze, followed the valley floor instead.
- Haze: Reduced visibility hindered situational awareness.
- Removed gyrocompass: The lack of this instrument made it difficult to detect the significant course deviation early enough to correct it.
The aircraft was airworthy, and the pilot held a valid license with no evidence of medical impairment. The mass and balance were within limits.
Safety action
The report highlights the risks associated with unfamiliar departure procedures and the importance of reliable navigation instruments during VFR flight in complex terrain.