What happened
On August 8, 1972, a private VFR flight departed from Speck-Fehraltorf, bound for Bern. Because the aircraft, a Super Falco F8L with registration HB-UOE, was not equipped with radio communications, the pilot followed standard procedures by obtaining landing clearance via telephone prior to departure. The air traffic control center instructed the pilot to land to the right of the runway vehicle on grass runway 32 L.
During the approach at 3200 ft/MSL, the pilot entered a left turn and began a descent. As the pilot reduced speed below 125 mph to extend the landing gear, the gear remained retracted. The pilot proceeded with the approach, extending flaps and reducing speed to 80 mph. The aircraft touched down 216 meters beyond the threshold of runway 32 L with the landing gear still up, resulting in a 281-meter excursion. The pilot was uninjured, and the aircraft sustained only minor damage.
The investigation
The investigation examined the mechanical state of the aircraft and the operational conditions at the airport. It was determined that the landing gear lever was in the "Up" position, and the cockpit indicators—including a red light and three mechanical gauges—correctly reflected that the gear was retracted.
Crucially, the investigation found that the landing gear warning horn, which is triggered by a switch on the power lever, failed to sound. This was due to a loose preload screw on the membrane of the horn. Because the horn rarely sounds during normal operations, this defect had gone unnoticed. Additionally, the investigation noted that the runway vehicle, which is responsible for providing visual light signals to non-radio-equipped aircraft, was not in position at the time of arrival due to a shift change in personnel.
Findings
Several factors contributed to the failure to extend the landing gear:
- The pilot experienced a lapse in concentration, specifically focusing too heavily on other aspects of the approach and forgetting to verify the gear position.
- The absence of expected visual light signals from the runway vehicle caused additional distraction and irritation for the pilot.
- The aircraft's warning system was inadequate; the warning horn was non-functional due to the mechanical defect, and the red cockpit warning lights were difficult to see due to sunlight glare.