What happened
On the evening of 2 April 2023, a Cessna C310Q, registration ZS-III, was performing a night flight from Upington Aerodrome to Rand Aerodrome. The aircraft, operated under private Part 9 and carrying a pilot and four passengers, was flying under visual meteorological conditions.
During the landing approach on Runway 35, the pilot confirmed that the landing gear was in the down and locked position, noting the three green indicator lights. However, during the landing roll, the left main landing gear suddenly collapsed. This caused the left wing and propeller to strike the runway surface, forcing the aircraft to veer off the runway and come to rest approximately 6 metres from the edge. While the aircraft sustained substantial damage, there were no injuries to the five people on board.
The investigation
SACAA AIID investigators examined the mechanical failure of the landing gear assembly. The investigation established that the left main landing gear retracted unexpectedly due to an overload failure within the locking mechanism. Specifically, the failure occurred at the bell-crank axis mechanism, where the adjusting screw eye-end attachment could no longer support the forces applied. This failure led to the destruction of the push-pull tube and further caused the propeller blades to strike the ground.
Findings
- The primary cause of the gear collapse was an overload failure of the locking mechanism.
- This failure was triggered by either pre-load stress introduced during a previous adjustment or an oscillatory motion caused by an incorrect, loose adjustment that amplified stress on the bell-crank.
- The manufacturer had previously identified similar risks in this aircraft type, issuing Supplemental Inspection Documents (SIDs) to monitor for wear and slack in the retraction system.
- Incorrect rigging during maintenance was identified as a contributing factor to the mechanical instability.