What happened
On the afternoon of November 10, 1979, a Beagle Pup B 121, registration HB-NAZ, departed from Porrentruy for La Chaux-de-Fonds with two passengers on board. Before takeoff, the airfield manager had specifically warned the pilot about dangerous snow squalls and low visibility over the hills, suggesting a northern route toward France where the sky was clearer. Despite this warning, the pilot proceeded with the flight.
As the aircraft traveled through the valley, it encountered severe weather, including heavy snow and rain. Witnesses near the Doubs valley reported hearing the engine revving at high power, suggesting a desperate attempt to regain altitude or a sudden maneuver, followed by a sudden silence. The aircraft subsequently crashed into a forest near Lac de Moron at an approximate descent angle of 70 degrees. The impact was so violent that all three occupants were killed, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and local meteorological data to reconstruct the flight. The aircraft was found with its nose heavily damaged, though the engine and wings remained largely intact. The investigation confirmed that the aircraft's weight and center of gravity were within safe limits and that no mechanical failures contributed to the crash.
Witness accounts provided a timeline of the engine noise, which indicated the pilot may have been performing an aggressive maneuver or struggling to maintain altitude. The investigation also noted that the pilot's radio telephony extension was not present on his license, and no radio communications were received during the flight.