What happened
On September 21, 1967, a student pilot was conducting a series of navigation and altitude tests required for a private pilot license. The flight began at Birrfeld, with the first leg proceeding to Granges. During the second leg, intended for Lausanne, the pilot encountered heavy headwinds that significantly slowed progress. Realizing the remaining fuel was insufficient to reach the destination, the pilot diverted to La Chaux-de-Fonds to refuel.
After landing safely and refueling, the pilot attempted to continue the flight. During the takeoff roll on runway 24, the aircraft was struck by a powerful gust of wind from the left. The pilot attempted to correct the imbalance, but the wind lifted the left wing, causing the Piper J3C to strike the ground with its right wingtip and rotate 180 degrees. As the pilot prepared to evacuate, a subsequent gust caused the aircraft to flip onto its back. The pilot escaped the HB-ONE without injury, though the aircraft sustained 75% damage.
The investigation
Investigators examined the meteorological conditions and the flight's planning. At the time of the accident, a deep depression was moving through the region, causing strong southwest winds and gusts in the lower atmosphere. While the wind at the airport was recorded at approximately 35 km/h, the investigation considered that a localized turbulence or gust, not captured by the anemometer located 200 meters away, likely caused the imbalance.
Findings
- The primary cause was that the flight instructor authorized the student to proceed with the required navigation and altitude tests despite meteorological forecasts predicting a rapid and significant deterioration in weather conditions.
- The instructor likely underestimated the severity of the worsening weather based on the calmer conditions observed earlier in the morning.
- The pilot's decision to divert was necessitated by high fuel consumption caused by strong headwinds.
- The aircraft was within weight and balance limits at the time of the accident.