Incident
Following takeoff of flight 4317, the main landing gear did not retract. The flight crew executed the emergency checklist, extended the landing gear, and subsequently made an uneventful landing.
Examination Findings
A detailed examination of the aircraft disclosed that the right landing gear retraction fitting had failed. Additionally, a hydraulic line was severed. The quantity limiting valves were found to be corroded, and their respective piston movement was restricted. Consequently, both hydraulic systems were drained of fluid.
Further examination of the fitting attachment bolts revealed that the top bolt had lost torque and failed in fatigue; the bottom bolts failed in overload. Additionally, the fitting spigot failed due to hydrogen embrittlement. To address the hydrogen embrittlement problems, an improved fitting has been produced.
Fleet Campaign and Directives
The operator conducted a fleet campaign and found 13 loose bolts in other 100 series aircraft. Subsequently, several airworthiness directives were issued to correct the loss of torque on attachment bolts. These directives included checking the torque at the 300-hour landing gear inspection.