Accident Overview
On 20 March 1966 at approximately 1525 MEZ, two Piper Super-Cub aircraft collided in mid-air over the Luzern-Beromünster airfield in the canton of Lucerne. The aircraft involved were HB-OYB, serving as a glider towing aircraft, and HB-OYC, which was on a normal traffic pattern flight. The collision occurred at an estimated altitude of 10 to 15 meters above ground, near the threshold of runway 34. Both aircraft became entangled and crashed, resulting in serious injuries to the pilot of HB-OYC and minor injuries to the pilot of HB-OYB. Both aircraft were destroyed.
Involved Aircraft
Both aircraft were Piper Super-Cub PA-18-125 models, equipped with Lycoming O-290-D engines and two-blade metal fixed-pitch propellers. They were high-wing strut-braced monoplanes with tandem seating and fixed tailwheel landing gear. Neither aircraft was equipped with radio communication. Both had dark gray paint schemes with white registration markings and orange warning paint on wingtips and leading edges. Weight and center of gravity were within limits, and no technical defects were found.
Pilots
The pilot of HB-OYB, born 1927, held a private pilot license issued November 1964, valid until June 1966. He had a total flight experience of 80 hours and 441 landings, including 19 hours 35 minutes on the accident type. In the three months prior, he flew 8 hours 14 minutes and 18 landings, all on the accident aircraft. No previous accidents or violations were recorded.
The pilot of HB-OYC, born 1934, held a private pilot license issued May 1965, valid until February 1967. He had a total flight experience of 86 hours and 459 landings, of which 49 hours and 392 landings were on motor aircraft, predominantly Piper Super-Cub. In the three months prior, he flew a 25-minute dual check flight with 5 landings on February 28, and 13 minutes solo with 3 landings on March 4. No previous accidents or violations were recorded. No health issues were indicated on the day of the accident.
Weather Conditions
The weather at the time was sunny with light cumulus clouds. Wind was from the northeast at 10 knots, visibility was good, and temperature was 5°C. The sun's elevation was 27 degrees with an azimuth of 235 degrees.
Flight Sequence
On the day of the accident, three pilots intended to complete required glider towing flights under the supervision of a chief flight instructor. After a briefing emphasizing airspace surveillance, the pilot of HB-OYB departed at 15:15 towing a glider (Ka-8). The tow proceeded normally. After the glider released at approximately 400 meters above ground, the towing pilot performed a right-hand circuit to lose altitude and drop the tow rope beside the runway. However, seeing an aircraft on final approach, he went around again. On the second attempt, he dropped the rope from about 100 meters, added power, and at midfield turned left to initiate a short circuit for landing. He reduced speed, set flaps to first notch, and after checking that the approach zone was clear, began a left turn with approximately 30 degrees of bank. He then fully extended flaps and entered a slight left sideslip. Shortly after, he saw someone on the runway waving a red flag. Looking to the right, he saw a wing appearing from below, and the collision occurred. He attempted to disengage but the aircraft remained locked together and crashed left of the runway threshold.
The pilot of HB-OYC had arrived about an hour earlier with the intention of flying a solo circuit and then a short flight with his fiancée. With agreement from the instructor, he took off after the towing aircraft departed. He flew the standard left-hand traffic pattern as published in the AIP. Before turning final, he checked the approach sector. On final, he focused on the runway where a group of people was moving. As he was about to flatten his approach, he saw the red flag waved by the instructor and added full power to go around. Immediately, he heard a sound from the left, and his aircraft began to roll left. He tried to correct but failed. He had not seen the other aircraft during final approach and only realized they had collided during the crash.
The chief flight instructor stated he was standing near the runway threshold. When HB-OYC was on final and HB-OYB began its landing turn, he took the red flag. He observed both aircraft and believed the pilot of HB-OYB must have seen HB-OYC, but when the towing aircraft made no evasive action, he waved the flag vigorously, hoping both would react. The pilot of HB-OYC apparently saw the signal, added power and climbed slightly, at which moment contact occurred at about 10-15 meters. The aircraft first flew straight ahead, climbed slightly to about 20 meters, then rolled and crashed.
Conclusion
The accident was essentially due to objectively insufficient airspace surveillance, particularly by the pilot of the towing aircraft.