What happened
On October 23, 1976, a Chipmunk T 22 A, registration HB-TUL, was performing a glider tow at Buttwil airfield. After releasing a Ka8 glider at approximately 700 meters, the pilot released the tow rope at an altitude of about 30 meters and initiated a standard circuit to land on runway 34.
During this period, a motor glider was preparing for takeoff on the same runway. To avoid contact with the discarded tow rope, the motor glider pilot delayed his departure. An observer on the airfield, concerned by the proximity of the aircraft, used hand signals to instruct the motor glider pilot to abort the takeoff. The tow pilot, observing both the moving motor glider and the person on the runway, decided to execute a tight, low-altitude turn to avoid the runway obstruction.
While performing this maneuver, the pilot became uncertain whether the tow rope had actually disconnected, as he was distracted by the hand signals on the ground. In an attempt to verify the status of the rope, the pilot repeatedly looked backward. This loss of focus caused the aircraft to fall below its minimum flying speed during the landing approach. The aircraft subsequently stalled, lost control, and crashed into a wooded ravine approximately 550 meters short of the runway threshold. The pilot escaped without injury, but the Chipmunk T 22 A was destroyed.
The investigation
The investigation established that the aircraft was properly maintained and that all mechanical systems, including the tow release mechanism and the rope indicator light, were fully functional. The pilot's medical health was found to be unimpaired, though the investigation noted the pilot had been involved in a similar accident with the same aircraft type in 1968.
Investigators examined the airfield conditions and found that the runway had been temporarily relocated due to construction. At the time of the accident, there was no radio communication or runway controller present to manage the simultaneous glider and motor glider operations. The investigation also confirmed that the aircraft's weight and center of gravity were within safe limits and that the weather conditions were clear with light winds.
Findings
- The pilot's decision to perform a low-altitude, tight turn was unsuitable flight tactics, as it placed the aircraft dangerously close to rising terrain.
- The pilot was distracted from essential flight tasks by attempting to visually verify the tow rope status while performing a complex maneuver.
- The aircraft's speed dropped below the minimum required threshold during the landing circuit, leading to the loss of control.