Cessna 310R N455TB accident near Great Falls, Montana

Probable cause

The uncommanded retraction of the right main landing gear during taxi due to the failure of the landing gear extension system to move the right main gear upper side link into the locked position for undetermined reasons.

NTSB analysis

While on approach to his planned destination, the pilot lowered the landing gear handle, but the green "gear down" light for the right main landing gear did not illuminate, and the "gear in transition" light stayed on. After checking the "gear down" light, which illuminated when pushed, the pilot reached the conclusion that the problem was most likely a bad gear position indicator switch, which was a problem he had experienced before. The pilot then considered cycling the landing gear, but decided not to do so in case there was something broken in the system that might result in the right main gear remaining up once it was retracted. He then executed an uneventful landing and rollout, which included slowing to his normal taxi speed. At that point he turned off the runway onto the taxiway, and as he began to straighten the airplane to follow the taxiway centerline, the right main gear to folded back, causing the right wing to impacted the taxiway. A postaccident inspection determined that the right main gear upper side link (over-center lock) had not moved fully to its locked position, and that the side-loads generated by the turn to align with the taxiway were transferred to the gear activation system. The transfer of those loads then resulted in the overload failure of the right main gear strut-mounted bellcrank. It could not be determined what caused the right main landing gear activation linkage to be far enough out of adjustment as to result in the upper side link not moving to its fully locked position.

Text from the NTSB. Open the NTSB docket for WPR10LA476 for the full record.