What happened
On 15 July 2011, a Cessna 340A, registration N346DW, was performing a private flight from Dunsfold Aerodrome to Fairoaks Airport. The flight was the second following a recent annual maintenance inspection. During the landing roll on Runway 24, the aircraft's right main landing gear collapsed. This caused the aircraft to veer off the paved runway onto the grass, resulting in the right propeller, right wingtip, and right flap striking the ground. The right engine also sustained shock-loading. The pilot, who was the sole occupant, was not injured.
The investigation
The investigation examined the aircraft's maintenance history and the mechanical state of the landing gear components. Records indicated that during recent maintenance, two worn bushes in the right main landing gear bellcrank had been replaced. However, the investigation found that the extensive 76-step landing gear rigging procedure required by the manufacturer's Service Manual had not been fully completed. Specifically, the 'free-fall' downlock link adjustment procedure was omitted.
Metallurgical analysis of the fractured downlock link adjusting screw and the bellcrank pivot bolt showed no evidence of fatigue, pre-existing cracks, or material defects. The analysis concluded that the failures were the result of single, non-reversed overload events.
Findings
- The right main landing gear collapsed during a normal landing, despite the pilot reporting that the gear had deployed normally with three green indicator lights illuminated.
- The right main landing gear components showed evidence of a bending overload failure of the downlock link adjusting screw and a single shear overload of the bellcrank pivot bolt.
- It is probable that the downlock link or side brace was not sufficiently over-centre, allowing side-loads to cause the brace to fold.
- The investigation could not definitively determine the cause of the collapse because the damage to the microswitch mounting bracket prevented functional testing of the gear system in its pre-accident state.