What happened
On July 9, 1973, a SZD 12A Mucha 100A glider, registration HB-624, departed from the Courtelary aerodrome on runway 07. Following a winch launch, the pilot released the aircraft above a ridge near Cortébert at approximately 700 m QFE. After failing to find sufficient thermal activity, the pilot transitioned toward Courtelary, reaching an altitude of 250 m QFE.
While attempting to maneuver, the aircraft encountered significant downdrafts of 3 to 4 m/s. Due to the loss of altitude and the strength of these sinking currents, the pilot attempted an emergency landing in a field adjacent to the Suze river. During a low-altitude turn intended to align with the field, the left wingtip struck a tree on the north bank of the river. The glider subsequently came to rest in the riverbed.
The investigation
The investigation examined the pilot's experience, the aircraft's airworthiness, and the prevailing meteorological conditions. The pilot was an experienced flyer with over 800 total hours, including 67 hours on this specific type. There were no indications of health issues or prior regulatory infractions. The SZD 12A Much00 A was found to be in a valid state of flight readiness, and no technical failures were identified as contributing to the crash.
Weather conditions at the time involved a Bise wind with light thunderstorm tendencies. While convection was low, moderate turbulence was present. Witnesses observed the glider performing several left-hand turns over Courtelary, noting that the aircraft appeared to be on final approach at altitudes of 150 m, 100 m, and finally 60 m, which surprised observers as the pilot continued to circle rather than land.
Findings
- The primary cause of the accident was an approach conducted at an altitude too low to safely reach the aerodrome.
- The pilot encountered downdrafts that depleted the aircraft's energy.
- There was a failure to adhere to local aerodrome procedures, which required gliders performing local flights to maintain a minimum altitude of 300 m AGL while in the holding pattern before initiating an approach at 200 m AGL.
- The pilot had previously received a warning regarding non-compliance with these specific altitude instructions.