Accident Overview
On 12 July 1961 at 1723 UTC, a Piper Cub L4H, registration HB-OEF, operated by Piper Club Basel and chartered by Balair, was involved in an accident at Basel-Mulhouse Airport in France. The aircraft was on a local training flight with a student pilot as the sole occupant. No passengers were on board.
Sequence of Events
The student pilot, who held a student pilot license issued on 24 May 1961, had accumulated 20.30 hours of total flight time, all on the accident aircraft type, with 155 landings (68 solo). At approximately 1700 UTC, he received authorization from his instructor to perform several circuits. He departed for his first circuit and landed successfully, though slightly short. After departing for a second circuit, a sudden and violent wind associated with a nearby thunderstorm developed, with wind direction 260° and speed 30 to 40 knots. The control tower activated runway 26 and illuminated the T, runway, and airport beacon to indicate the change. Two other Piper aircraft in the vicinity landed normally on runway 26.
The student pilot, however, continued to attempt landings on runway 34 despite signals from his instructor on the ground and from the control tower to abort. After two unsuccessful attempts, he made a third approach with the apparent intention of landing on runway 34. Shortly before touchdown, the aircraft turned right and landed on the grass with a trajectory roughly aligned with the wind direction. After rolling approximately 200 meters, the aircraft overturned and came to rest inverted. The pilot freed himself and emerged from the accident uninjured.
Damage Assessment
Initial assessment indicated 20 to 30 percent damage. A more detailed inspection revealed: right wing upper surface 100% destroyed, left wing upper surface 30% destroyed; fuselage slightly deformed in the middle; vertical stabilizer and rudder 40% damaged; windshield broken, vertical frame deformed; propeller broken; engine cowling dented; carburetor air filter destroyed. The aircraft was estimated to be 30% damaged, but full repair would require stripping and recovering the wings. No pre-existing defects or malfunctions were found; the engine operated normally throughout the flight. Fuel on board (46 liters at departure, maximum 25 minutes of flight) ruled out fuel exhaustion.
Meteorological Conditions
The weather had been thundery throughout the afternoon, but the cloud formations did not indicate serious concern. The thunderstorm was located southwest of the airport and was not expected to affect the area. Local flights had been authorized. Balair instructors had consulted the meteorological service and were aware of the thundery conditions but did not anticipate rapid deterioration. Wind records at the airport showed: from 1600 to 1640 UTC, wind calm to 2-3 knots; 1640-1710 UTC, calm to 6-9 knots; 1710-1715 UTC, 240°-260° at 20-25 knots; 1715-1725 UTC, 260° at 30-35 knots, then decreasing to 8-28 knots between 1800 and 1830 UTC. The rapid increase occurred between 1710 and 1715 UTC, when wind speed rose from 9 to 25 knots.
Air Traffic Control and Safety Actions
As soon as the sudden wind was observed shortly after 1700 UTC, control tower personnel attempted to contact Balair supervisors by phone, but there was no direct communication with instructors on the grass strip. The controller sent someone to the grass strip while implementing measures to change landing direction. A Flyco vehicle was positioned near runway 26, and airport safety vehicles were stationed at potential accident sites. The shift supervisor did not have time to descend from the tower and reach the grass strip before the wind increased. However, Balair personnel on the ground had already begun signaling students to avoid landing on the grass strip.
Probable Cause
The initial cause of the accident lies in a pilot error: he did not use the most advantageous landing direction, which was also the imposed one. The reasons for his choice were not established. The pilot was scheduled to give a statement the day after the accident but left town for an indefinite period without presenting himself to the investigator. It appears he told his instructor that he thought he was landing into the wind, whereas he actually landed downwind. It is likely that during the landing roll, he kept the elevator control back, which placed the elevator under maximum wind effect and facilitated the tail lifting under gusts; under those conditions, minimal brake input could cause the aircraft to overturn. The inexperienced pilot became somewhat flustered by the unexpected situation and did not realize he could have landed facing west, as other aircraft did.