Piper J3C Crash on Final Approach at Buttwil (HB-OXP)

Aircraft and Pilot Information

• Aircraft: Piper J3C 90 PS (67 kW), registration HB-OXP, privately owned and operated.
• Pilot: Swiss citizen, born 1943, held a private pilot license. Total flight time: 250 hours (34 hours in last 90 days). On type: 207 hours (24 hours in last 90 days).

Flight History

On 2 December 1983, the pilot departed Buttwil airfield at approximately 1300 local time for a reconnaissance flight toward Titlis and Tödi. The flight was routine until reaching the Rigi area, where strong Bise turbulence was encountered. The pilot decided to abort and return to Buttwil via Aegerisee and Affoltern a.A.

Accident Sequence

On final approach to runway 34 at Buttwil, the pilot observed strong sink (about 5 m/s) and severe turbulence. He abruptly added power, but the engine did not deliver full power in time. The minimum flying speed was undershot, causing the left wing to contact treetops. The aircraft stalled and crashed approximately 500 meters before the runway threshold with virtually no forward speed. The pilot sustained serious injuries; the aircraft was destroyed.

Findings

• The pilot held valid licenses and was authorized for the flight.
• Aircraft documents were in order; weight and center of gravity were within limits. No known technical issues influenced the accident.
• Buttwil airfield sits on a terrace of Lindenberg. During Bise conditions, upwinds and gustiness near the ground, especially over the forest ahead of runway 34, are known to local pilots.
• Weather at the time of the accident: wind from NE at 10-15 knots, gusts to 30 knots; visibility over 10 km; clouds 2-3/8 cirrus; temperature -2°C, dew point -10°C; pressure 1031 mbar; hazard: local Bise turbulence.
• The Piper J3C is flown single-seat from the rear seat. The pilot stated he maintained sight of the runway during final, which would not be possible at an extremely high angle of attack.
• Approach speed was 100 km/h, compared to the normal 90 km/h.
• The pilot habitually aimed for a touchdown point 100-200 m past the threshold.

Cause

The accident was due to inappropriate flight tactics in the final approach under difficult wind conditions.