What happened
On the afternoon of September 20, 1979, a Mooney M20F, registration HB-DVI, departed Neuchâtel airport for a flight to Bern. Prior to departure, the pilot had been coordinating with a mechanic to repair a defective DME unit. Despite being warned by a flight instructor on the ground that weather conditions were extremely poor—characterized by a thick cloud ceiling and low visibility—the pilot intended to proceed under Instrument Flight Rules (IFR).
Shortly after takeoff, the aircraft entered an area of heavy fog and rain. Witnesses on the ground, including two woodcutters working on the southern slope of the Chaumont, reported hearing the aircraft's engine power fluctuate several times. The aircraft subsequently struck the rising, wooded terrain at an altitude of approximately 1,000 meters. The impact destroyed the aircraft and caused the death of the pilot.
The investigation
Investigators examined the wreckage and the pilot's flight preparations. The aircraft's weight and balance were found to be within limits, and the engine and airframe showed no evidence of pre-existing mechanical failures. The investigation also reviewed the pilot's credentials, noting he was a highly experienced IFR pilot with over 1,400 flight hours.
Meteorological data confirmed that while the cloud ceiling at Neuchâtel was around 3,000 feet, lower stratus clouds were resting against the Jura mountains. The investigation also noted that the pilot had inquired about IFR approach procedures at La Chaux-de-Fonds earlier that day, suggesting a possible change in intended routing.
Findings
- The pilot was legally qualified and physically fit to conduct the flight.
- The Mooney M20F was airworthy and properly maintained.
- The pilot encountered a sudden transition from visual to instrument meteorological conditions.
- A navigation error occurred during the transition from VFR to IFR conditions.
- The pilot may have become disoriented while simultaneously managing navigation instruments and flight charts.
- Fluctuations in engine power observed by witnesses suggest the pilot may have struggled to maintain altitude or orientation while encountering unexpected clouds.