What happened
On Saturday, August 20, 1983, a Piper PA-28-161 Warrior registered PH-RAV departed from Bern-Belp Airport at 11:39 local time. The aircraft was operated by two pilots and carried three passengers, including an infant, on a private VFR flight intended for Basel. Before reaching the destination, the crew diverted to photograph a colorful sailboat regatta on Lake Thun. Witnesses confirmed that the aircraft conducted extremely low-level passes, sometimes as low as 20 meters above the water surface, for approximately 15 minutes.
After leaving the lake area, the pilot entered the Lombach valley near Unterseen at a relatively low altitude. The aircraft then climbed to approximately 1,200 meters before entering the narrower Traubachtal valley north of Interlaken. As the terrain rose steeply and the valley narrowed, the aircraft struggled to maintain altitude. It collided with two fir trees and subsequently crashed onto rocky ground near Habkern at an elevation of 1,600 meters. The accident occurred around 12:08 local time.
The investigation
The Swiss Transportation Safety Investigation Board (STSB) examined the wreckage, witness testimonies, and flight records. The aircraft was found destroyed with significant forest damage in the vicinity. Technical inspections revealed no mechanical failures; the engine was delivering power at impact, and all control surfaces were functional. Medical examinations of the pilots showed no signs of alcohol, medication influence, or pre-existing organic diseases.
The investigation focused on operational factors and pilot decision-making. The aircraft had been fully fueled, and its weight and balance were within limits. The flight plan was not filed with Air Traffic Control, which delayed the initiation of a search operation until the aircraft was discovered two days later by a private individual. The primary focus remained on the flight path analysis through the complex mountain terrain.
Findings
The accident was caused by incorrect flying tactics in mountainous terrain. Specifically, the pilot entered an unpredictable valley without sufficient altitude reserve to ensure safe passage or reversal. The crew failed to accurately estimate their vertical trajectory relative to the rising valley floor and missed the last viable opportunity to turn around.
Contributing factors included:
- Lack of mountain flying experience: The pilots were unfamiliar with the specific challenges of navigating narrow, steep valleys.
- Geographical disorientation: There was a possibility that the pilots confused the Lombach valley with another route, such as the Justistal or Brünig pass, leading to late recognition of their position.
- Visual illusion: The steep climb required to stay above the terrain created a false sense of security for inexperienced pilots, who may have perceived the sky ahead as clear while actually being below the ridge line.
Safety action
The investigation highlighted that the lack of a filed flight plan contributed to the delay in locating the wreckage. For domestic VFR flights, filing an ATC flight plan is optional but recommended to ensure automatic search initiation if the aircraft fails to arrive at its destination. The report emphasized the critical importance of maintaining adequate altitude reserves when entering uncharted or complex valleys to allow for geographical orientation and emergency maneuvers.