What happened
A flight test mission was being conducted to gather data on the production configuration of the stall warning system and improvements to the landing gear warning system. During takeoff, a discrepancy occurred within the landing gear warning system, characterized by the activation of the gear warning horn and an unsafe gear indication while the landing gear remained retracted. The aircraft climbed to 8,000 feet for planned testing.
Following the tests, it was observed that the gear warning would persist unless throttles were reduced to approximately 14 inches manifold pressure. The flight returned to the departure airport while the warning horn and unsafe gear annunciator remained active. During the base leg of the approach, the pilot lowered the landing gear selector handle and confirmed three green lights indicating the gear was down and locked. This status was confirmed twice more during the final approach.
The Piper aircraft touched down on the main landing gears followed by the nose landing gear. Upon reducing back pressure, the aircraft suddenly pitched nose down as if the nose gear had collapsed. The pilot observed the airplane sliding on the runway in a level attitude, suggesting a main gear collapse. During the slide, the right wing collided with a taxiway sign. The aircraft spun approximately 150 degrees to the right and came to rest upright on the grass. After the aircraft stopped, it was noted that only the left main down and locked light was illuminated. Following the occupants' exit, fuel leakage from the right fuel tank was observed. There were no injuries.
The investigation
An FAA inspector examined the aircraft four days after the accident using an external power cart. With the landing gear selector in the down position, the aural gear warning horn sounded and no down and locked light was observed for the left main landing gear. Investigators attributed the horn and light malfunction to the main landing gear actuator attach point being sheared. After bypassing the left main landing gear down microswitch, the light illuminated and the horn stopped.
When attempting to retract the landing gear, there was no movement or sound from the normal hydraulic pump; however, the gear retracted when the pump was supplied power directly. Attempts to extend the nose and right main landing gears using direct power to the hydraulic pump were unsuccessful, and they could not be forcefully unlocked. The only noted discrepancy was that the nose landing gear over-center locking device appeared to have some play, though a comparison with a new production aircraft showed no such evidence of play.
A post-accident rigging check by New Piper Aircraft, Inc. revealed no abnormalities. Records indicated the nose gear and torque links had been inspected for wear limits and reinstalled following a gear swing check in September 2002.