Incident Overview
A pilot reported that during the landing sequence, no gear movement occurred when the gear selector was initially lowered. After recycling the switch, the landing gear extended, but the gear down indicator did not illuminate. The control tower confirmed that the gear appeared to be down. The pilot then performed a manual extension of the landing gear and subsequently observed a down-locked light. However, during the landing rollout, the landing gear retracted.
Examination Findings
Post-incident examination of the aircraft revealed excessive play in the linkage of both the left and right main landing gear. Specifically, the left main gear could extend but would not achieve the over-center position in the down configuration when using manual extension. Additionally, a broken wire was found within its insulation at the left gear down switch. The break occurred in an area where the wire flexes as the landing gear cycles.
Safety Device Information
Later production models of this aircraft include a landing gear down safety device designed to mechanically lock the gear in the down position when extended manually. According to the source, a service spares letter published in 1973 announced the availability of this device for retrofitting on earlier production airplanes.