Flight History
On Easter Monday, 23 April 1973, the pilot conducted a private flight with three passengers from Zurich to Sitten and back in a Cessna Cardinal F 177 RG, registration HB-CWD. Landing at Sitten was abnormal: the aircraft touched down short of the marked threshold and the main landing gear rolled over the lowered cables of the arrestor net. The pilot did not report this occurrence. At 1500 MEZ, the return flight to Zurich was initiated. During gear retraction, the yellow indicator lamp (for gear up and locked) did not illuminate. The pilot extended the gear, but the green indicator lamp (for gear down and locked) also failed to illuminate. Repeated extension and retraction cycles did not resolve the discrepancy. The pilot chose to continue to Zurich with the gear lever in the "Up" position and without the yellow gear indication. He noted that cruise speed was slightly below normal at the usual throttle setting.
On approach to Zurich, the pilot extended the gear early, but the green lamp did not illuminate. He overflew the control tower for a visual check; the tower reported that the gear appeared extended and normal. When the pilot reduced throttle, the gear warning horn sounded. He decided to go around and manually extend the gear by turning off the electric hydraulic pump and using the hand pump, but could not achieve a green light. The pilot requested a landing on runway 28 and declined an offer of advice from a technical specialist on the ground. Over the runway threshold, he precautionarily turned off the master switch and ignition, closed the fuel valves, and unlocked the door. The aircraft touched down at 1640 on what appeared to be locked main gear, but after a short roll it nosed over and slid on the nosewheel fairing. No fire occurred.
Aircraft Information
The aircraft, a Cessna Cardinal F 177 RG (HB-CWD), possessed a valid airworthiness certificate and was approved for operation. No pre-existing defects were found. Examination revealed that the mechanical-electrical control mechanism of the landing gear had been damaged by a strike on the right main gear. After jacking up the aircraft in the hangar, gear retraction and extension functioned normally. However, after repair, further locking issues emerged in flight, which only resolved after replacing the apparently damaged control solenoid of the right gear. At the time, no specific checklist for landing gear malfunctions existed; the English-language Owner's Manual did not fully cover a simultaneous extension and retraction fault.
Pilot Information
The pilot, born in 1930, held a valid private pilot license. His total flight experience was 128 hours, including 9 hours on the accident type. In the preceding 90 days, he had flown 5.5 hours, of which 3.5 were on the accident type. No evidence of health issues at the time was found, and no prior incidents were recorded in the Federal Air Office files.
Investigation and Findings
The investigation determined that the landing gear control system was damaged when the aircraft rolled over the lowered cables of the arrestor net during the landing at Sitten. The pilot should have reported this occurrence before the return flight. He did not fully follow manufacturer's procedures after the gear fault appeared, initially suspecting only an indication malfunction. However, subsequent testing showed that even with correct procedures, the gear would not always lock in flight due to the damaged control mechanism. At Zurich, the main gear appeared to lock, but the nose gear remained unlocked and collapsed during rollout.
Probable Cause
Damage to the landing gear control system caused by rolling over an obstacle during the preceding landing.