What happened
On April 30, 1978, a Piper PA-18-150, registration HB-OZE, was performing a glider tow operation near Gaissau, Austria. The flight began normally, with the aircraft successfully performing several initial climbs. However, during a left-hand turn intended to transition into the downwind leg, a significant altitude discrepancy developed between the tow plane and the glider, an ASW 15 (registration HB-1029).
As the glider climbed higher than the tow plane, the tension on the tow rope pulled the tail of the aircraft upward. This forced the Piper PA-18-150 into a steep, nose-down dive. The pilot was unable to recover the aircraft from this pitch attitude. During the descent, the tow rope snapped. The aircraft struck a wooded area at a 30-degree angle, resulting in a post-impact fire that claimed the life of the pilot. The glider pilot, having become disconnected, was able to return to Altenrhein aerodrome and land safely.
The investigation
Investigators examined the flight dynamics, the mechanical state of the tow equipment, and the experience levels of the crew. The inquiry established that the tow rope utilized a specialized breaking point, but the values used for these points were higher than required by established regulations. The investigation also noted that while both aircraft were equipped with radios, they were operating on different frequencies, preventing communication between the two pilots.
Technical analysis focused on the use of a center-of-gravity (CG) attachment point rather than the traditional nose attachment. The investigation found that the glider pilot, who was undergoing training on this specific model, failed to maintain the aircraft's altitude relative to the tow plane. Instead, the pilot allowed the glider to climb, which directly induced the tow plane's pitch instability.
Findings
- The primary cause of the accident was the glider climbing above the tow plane, which physically lifted the tail of the aircraft.
- A contributing factor was the use of a center-of-gravity attachment for the tow, which makes the aircraft more susceptible to pitch changes compared to a nose attachment.
- The limited experience of the glider pilot on the ASW 15 model contributed to the failure to maintain proper altitude alignment.
- The tow rope failed due to the extreme tension caused by the forced dive of the aircraft.