N9158DMooney M20J · 1992

After arrival to the destination airport near the conclusion of a cross-country flight the private pilot reported the landing gear circuit breaker (CB) tripped after he attempted to lower the landing gear electrically via the normal method. He reset the CB and again attempted to lower the landing gear via the normal method, but the same CB tripped. He overflew the airport then flew towards the coast where he reviewed the airplane’s Pilot’s Operating Handbook and attempted multiple times to manually lower the landing gear but was unsuccessful. He also contacted his mechanic to obtain assistance, but he was unable to lower the landing gear. At the suggestion of his mechanic, he diverted to a larger nearby airport where he performed a go-around on the first approach because the flight was too fast, then returned and landed gear-up.

According to maintenance personnel associated with recovery of the airplane, lowering the landing gear required them to disconnect the push/pull tubes near the landing gear actuator for each landing gear. Further, the emergency cable activation lever would not move and was “jammed….” Following removal of the push/pull tubes near the actuator the emergency cable activation lever would only travel about 90%. Following removal of the actuator from the airplane, manual operation revealed the actuator turned freely in the retracted direction but would not turn in the gear extension direction. Disassembly inspection of the clutch drive assembly of the landing gear actuator revealed one “tang” of the torsion spring associated with gear extension was fractured. By system design the emergency extension system did not bypass the clutch and damaged spring; thus, a single point failure (torsion spring) precluded manual and normal extension of the landing gear. According to airframe manufacturer, the landing gear actuator and fractured torsion spring are no longer available or supported, but they do have a retrofit for the landing gear actuator.

An airframe manufacturer service instruction specified replacement of the torsion spring in the drive clutch assembly of the landing gear actuator was last performed nearly 5 years and 427 hours earlier. The service instruction, due every 1,000 hours, was due again in about 573 hours. The mechanic who performed the airplane’s last annual inspection nearly 8 months and 49 hours earlier reported that as part of that inspection he performed in part, normal and emergency extension checks of the landing gear and found no issues. He did not perform any maintenance to the landing gear except for lubrication.