What happened
On 27 December 2000, a Maule MX-7-180A, registration G-LOFM, was performing a private flight from Coventry Airport to Manston Airport. While executing a visual approach to Runway 10, the pilot was cleared to land with winds reported at 8 knots. The aircraft approached the threshold at approximately 60 MPH with full flaps selected.
During the flare, the pilot applied full into-wind aileron and achieved a three-point landing. To counteract a leftward swing, the pilot applied full right rudder, full nose-up elevator, and utilized the right wheel brake. Despite these efforts, the aircraft continued to yaw to the left. Upon noticing the right wheel skidding, the pilot released the brake, at which point the aircraft swung violently into the wind, causing the right wingtip and a/c aileron to strike the ground. There were no injuries to the two occupants.
The investigation
The investigation focused on the functionality of the aircraft's steerable tailwheel assembly. This system features a disconnect mechanism designed to allow the tailwheel to castor for improved low-speed ground maneuvering. Investigators discovered that a portion of the locking pin was missing, suggesting it had either sheared during the accident or was already broken. Furthermore, two pins retaining the bellcrank to a pivot assembly were found to have sheared.
Records from the operating company indicated that the retaining pins had been replaced at least four times in the preceding three years. Structural analysis of the locking pin remnant revealed evidence of stress corrosion, likely caused by the constant pressure of the pin against the ramp plate from the return spring load. The corrosion patterns suggested the final fracture of the pin had actually occurred well before the accident.
Findings
- The aircraft's tailwheel steering mechanism was likely inoperative prior to the accident due to a previously failed locking pin.
- The failure of the tailwheel locking pin meant the steering would only disconnect when the remaining retaining pins were subjected to enough force to shear them.
- The locking pin had been weakened by stress corrosion.
- The aircraft's tailwheel steering only disconnected during the landing roll when the secondary retaining pins sheared under the load of the maneuver.