What happened
On July 24, 2011, at approximately 15:27 JST, a privately owned SOCATA TB2B, registration JA4123, experienced a landing gear retraction while taxiing on the apron at Tajima Airfield. The aircraft, which was being operated for a flight from Tajima to Nagoya, was occupied by the pilot and the aircraft owner. During the taxi maneuver, the left-hand main landing gear retracted, causing the left wing to strike the ground surface. The impact resulted in substantial damage to the aircraft, including cracks in the wingtip cover and deformation of the wing structure near the flap hinge. No injuries were reported.
Prior to the accident, the aircraft had arrived at Tajima from Nagoya. During that earlier flight, the crew had encountered issues with the landing gear system, specifically a circuit breaker that repeatedly popped. To land safely, they had utilized the emergency landing gear extension knob. During the subsequent pre-flight check at Tajima, the crew noted that the landing gear position indicator lights were not showing the expected down-locked status, but they proceeded with the flight after the owner concluded the gear was properly locked.
The investigation
The Japan Transport Safety Board (JTSB) conducted an investigation that included on-site examinations and a teardown of aircraft components. Investigators focused on the landing gear extension and retraction system, specifically examining the landing gear UP and DOWN relays.
Testing revealed that the landing gear UP relay installed in the aircraft was incompatible with the aircraft's electrical system. While the aircraft operated on a 28V power supply, the installed relay was rated for only 12V. This mismatch caused the relay coils to overheat, leading to the degradation and partial melting of the contact points. Furthermore, the investigation found that the landing gear system was prone to moving into the UP position even when the lever was set to the DOWN position due to the compromised state of the electrical components.
Findings
- The primary cause of the accident was that the crew began taxiing the SOCATA TB2B without the landing gear being properly down-locked. This caused an imbalance in the load between the landing gear actuators, leading to the unintended retraction of the left-hand main landing gear.
- The crew failed to implement appropriate maintenance measures despite being aware of the landing gear system malfunctions during the previous flight.
- The crew did not correctly interpret the landing gear position indicator lights during the pre-flight check, which indicated the gear was out of the down-lock position.
- An incorrect electrical component (a 12V relay) had been installed in a 28V system, likely during manufacturing, which caused the relay contact points to deteriorate and fail.