Summary
On 27 May 1967 at 1504 Central European Time, a Piper Cub aircraft (registration HB-OSU) was involved in an accident near Biel-Kappelen airfield. The pilot, born in 1926 and holder of a valid private pilot license with about 42 total flight hours (including 1 hour 40 minutes since his private pilot exam on 24 September 1966), had exclusively flown Piper Cubs. The aircraft was properly certified, airworthy, and within weight and balance limits. The weather played no role.
Investigation
The airfield Biel-Kappelen, opened a few months prior, has a grass runway 05/23 measuring 630 meters in length and 30 meters in width at an elevation of 438 meters. The aircraft was equipped with a carburetor air preheating device.
On the day of the accident, the pilot completed several short flights. After two solo circuits of 10 minutes each, he flew a passenger to Grenchen and returned to Biel-Kappelen to pick up another passenger, landing at 1500. At 1504, he took off again with the passenger without first verifying that the carburetor preheat was off (pushed in). The aircraft lifted off with difficulty and the pilot soon noticed the preheat was on. He immediately switched it off but found himself at very low altitude approaching an electric power line. He decided to fly under the line and turned to avoid a pole, but the left wingtip collided with a concrete locality sign on the Lyss-Biel road. Approximately one meter of the wing was sheared off, but the aircraft remained sufficiently flyable and controllable. The pilot landed without further damage after about 300 meters. Both occupants were uninjured.
Discussion
The pilot himself noted that after the previous landing, he forgot to push in the carburetor preheat, and during takeoff preparations he omitted the corresponding check. Because the engine with preheat engaged produces significantly reduced power, the takeoff was long and shallow. By the time the cause was found and corrected, the aircraft was already close to the power line obstacle. While attempting to maneuver the aircraft between two poles, the low left wingtip struck the road sign.
Conclusion
The accident must be attributed to inadequate pre-takeoff preparation.