Incident Overview
During a flight arriving over Chicago, Illinois, the crew experienced a malfunction when the landing gear failed to extend. After multiple unsuccessful attempts to lower the gear, the crew decided to return to their home base airport to perform a gear-up landing. The landing was executed successfully, and no injuries were reported.
Investigation Findings
A subsequent investigation revealed the cause of the malfunction. A locking nut had backed off a tapered pin located at the inboard universal joint in the left main gear extension/retraction torque tube. This allowed the tapered pin to work itself out, disconnecting the torque tube from the gear drive motor and preventing gear extension. Investigators found no evidence of factory torque stripping on the nut.
Conclusion
The incident was attributed to the loosening of the locking nut, which led to the disconnection of the torque tube and subsequent landing gear failure.