What happened
On June 29, 1971, a Phoebus C Standard glider, registration HB-960, was involved in an accident during the final approach to the Montricher airfield. The flight began with a tow from Neuchâtel airfield, with the pilot releasing the tow cable at approximately 1,700 meters near Orbe. The pilot intended to glide toward Montricher, passing over the airfield at an altitude of 500 meters.
While attempting a landing on runway 03, the pilot encountered significant turbulence and downdrafts. As the aircraft transitioned into a left-hand downwind leg, the pilot's altitude decreased rapidly. In an attempt to compensate, the pilot shortened the landing pattern and initiated a 180-degree turn roughly 150 meters before the runway threshold. During this maneuver, the glider experienced a stall on the left wing and struck the ground. The aircraft came to rest on its back in a field at 19:15. The pilot sustained grievous injuries, and the glider was heavily damaged.
The investigation
The investigation confirmed that the pilot held a valid glider license and possessed good flight experience, with no evidence of health issues affecting performance on the day of the accident. The HB-960 was found to be in excellent mechanical condition with a valid certificate of airworthiness, and both weight and center of gravity were within prescribed limits. Technical failure was ruled out as a cause.
Weather conditions at Montricher were characterized by good visibility but significant wind activity. A West-Northwest wind of 10 to 15 knots was blowing, creating moderate turbulence near the terrain. This specific wind pattern, known locally as the "joran," produces gusts perpendicular to the Montricher runway.
Findings
- The pilot likely underestimated the strength of the crosswind, resulting in the aircraft being positioned too low and too close to the runway centerline at the end of the downwind leg.
- The primary cause was a loss of airspeed during a turn in turbulent conditions, which led to a left-wing stall.
- The altitude at which the stall occurred was insufficient to allow the pilot to recover to a normal flight attitude.