What happened
On the evening of July 11, 1967, a pilot was conducting night landing training at Zurich-Kloten Airport. The flight involved several touch-and-go maneuvers in a Beechcraft D-35 Bonanza, registration HB-EGZ, carrying three passengers. The aircraft was performing a series of landings on the West runway to fulfill requirements for the renewal of the pilot's night flying rating.
During the fifth landing of the session, the aircraft touched down smoothly on its main gear at approximately 95-100 knots. Shortly after touchdown, the pilot switched off the landing lights. As the aircraft continued its rollout, the nose gear collapsed. This caused the aircraft's nose to drop toward the runway, leading the propeller to strike the concrete, which subsequently caused the engine to stall. The aircraft slid for approximately 750 meters before coming to a halt. All four occupants escaped the incident uninjured, though the aircraft sustained substantial damage.
The investigation
Following the incident, the Swiss Transportation Safety Investigation Board (SUST) examined the mechanical and electrical systems of the landing gear. Investigators found no pre-existing defects in the gear's operation, and the pneumatic pressure in the struts was within regulatory limits. However, the structural tube strut responsible for the nose gear's movement was found to be buckled.
Investigators also reviewed the cockpit controls. The landing gear selector is located on the right-side instrument panel, positioned immediately adjacent to the landing light switches. To retract the gear, the pilot must first move a locking pin and then lift the gear lever. The investigation noted that the landing lights had indeed been turned off at the time of the accident.
Findings
- The primary cause of the accident was likely a reflexive or accidental movement of the landing gear lever by the pilot.
- It is believed that while attempting to turn off the landing lights, the pilot inadvertently disengaged the locking pin and briefly moved the gear lever to the up position.
- Because the gear was unlocked and partially retracted, the nose gear strut was unable to withstand the longitudinal impact forces of the rollout, leading to the buckling of the strut.
- The investigation concluded that the retraction process was likely extremely brief, which explains why the cockpit warning horn was not noted by the occupants.