Introduction
On 17 July 1968, a Piper Cherokee PA-28-180, registration HB-OZD, was involved in an accident at Grenchen airfield. The aircraft was owned by the Segelfluggruppe Grenchen. The flight was a conversion training session for the pilot.
Aircraft and Crew Information
The aircraft was a 1967 Piper Cherokee PA-28-180, serial number 28-4564, powered by a 180 hp Lycoming O-360-A4A engine. It had a fixed tricycle landing gear and mechanical flaps. At the time of the accident, the weight was approximately 1003 kg, within limits. The flight instructor, born in 1938, held a private pilot license and a provisional motor flight instructor certificate, with over 2000 hours of motor flight experience. The conversion pilot, born in 1942, held a private pilot license with approximately 194 hours of motor flight experience. Two passengers were also on board.
Weather and Airport Conditions
The weather was overcast and rainy. Grenchen airfield has a grass runway 580 m long and 30 m wide, oriented 25-07. Runway surfaces were wet from rain.
Flight Sequence and Accident
During the evening of 17 July 1968, the conversion pilot preflighted the aircraft. The flight instructor later joined and invited two students from a pre-flight course to accompany them. During taxi, the instructor explained his principle that a pilot should keep one hand on the throttle during takeoff and landing. He warned that he would pull the throttle to idle if the student did not comply. During the first takeoff, the student released the throttle to grip the yoke with both hands, and the instructor immediately reprimanded him.
After a familiarization flight, the instructor began landing training. The first approach was aborted due to overshooting. On the next approach, the instructor instructed the student to perform a touch-and-go if the landing was satisfactory. The landing occurred about 150 m past the landing T, and the instructor called "go." The student applied power. The instructor raised the flaps to position 1, but the student instinctively reached for the flap lever with his right hand, releasing the throttle. The instructor immediately pulled the throttle to idle. This occurred approximately two-thirds down the runway. The instructor told the student to brake. The student, surprised by the throttle retraction, momentarily tried to reapply power but found the throttle blocked by the instructor. The instructor repeated the brake command. Braking on wet grass was poor. The aircraft neared the runway end and a public road crossing perpendicularly. The instructor directed the student to use directional changes to extend the stopping distance, then called for a "cheval de bois" (ground loop). The student, fearing structural damage, preferred to cross the road straight ahead, noting an approaching car had stopped. The aircraft rolled over the raised road and came to rest in a cornfield.
Damage and Injuries
The four occupants were not injured. The aircraft sustained damage to the landing gear, wings, and fuselage, estimated at 12% of its value. No third-party damage occurred.
Later Findings
The aircraft had hydraulic wheel brakes on the main gear, operated by pedals on the left seat only. A handbrake lever under the instrument panel could be used from both front seats. The nosewheel was linked to the rudder pedals.
Conclusion
The official finding stated that the accident was caused by inappropriate intervention by the flight instructor during a go-around he had ordered.