What happened
On April 23, 1973, a private flight involving a Cessna Cardinal F 177 RG, registration HB-CWD, was traveling from Zurich to Sion and back. During the initial landing in Sion, the pilot landed short of the runway threshold, causing the main landing gear to run over the cables of a lowered safety net. The pilot did not immediately report this incident.
During the return flight to Zurich, the pilot noticed that the landing gear indicator lights were malfunctioning; specifically, the yellow light failed to indicate gear retraction, and the green light failed to indicate that the gear was locked. Despite attempting to cycle the gear and noticing a slight decrease in cruise speed, the pilot continued the flight with the gear lever in the up position. Upon approaching Zurich, the pilot attempted to manually extend the gear using the hand pump after the hydraulic pump was deactivated, but the green indicator remained unlit.
During the landing on runway 28, the main gear appeared to be locked, but the nose gear failed to lock properly. As the aircraft decelerated, the nose gear collapsed, causing the aircraft to tilt forward and slide on the nose gear assembly. There were no injuries to the pilot or the three passengers, and the aircraft sustained only minor damage.
The investigation
The investigation focused on the mechanical state of the landing gear and the pilot's actions following the landing in Sion. Investigators examined the aircraft's maintenance history and the physical condition of the landing gear components. The investigation established that the aircraft was airworthy and the pilot had no prior history of incidents or health issues that would have contributed to the event.
Findings
- The primary cause of the accident was damage to the landing gear control mechanism caused by striking the safety net cables during the landing in Sion.
- The impact on the right main gear damaged the electromechanical control mechanism, specifically the control solenoid.
- The pilot failed to report the initial landing incident in Sion, which prevented timely inspection of the gear.
- While the pilot did not strictly follow manufacturer instructions regarding gear extension procedures during the flight, this was deemed secondary, as the mechanical failure would have persisted regardless of the manual pumping attempts.
- The nose gear remained unlatched during the final landing, leading to the collapse.