Background
On 22 December 2002, a Cessna 402B aircraft registered ZS-NLU conducted an aerial survey flight from Wonderboom to the Ulundi area in KwaZulu-Natal. After completing the survey, the aircraft landed at Richards Bay to refuel for the return flight. The crew consisted of a commercial pilot and another crew member. The pilot had 3948.6 total flying hours, with 499.8 hours on type.
Accident Sequence
During the approach to Richards Bay, cockpit indications were normal, and the landing gear indication lights showed all three gears down and locked. On touchdown, however, the left wing began to drop, and the gear warning horn sounded as the left main gear collapsed. The pilot immediately initiated a go-around and retracted the landing gear. After retraction, the "gear in-transit" warning light extinguished, but the left main gear indication remained showing down and locked. The pilot noted that airspeed indication and the absence of asymmetric drag suggested the left gear had indeed retracted.
The pilot declared an emergency and decided to return to Wonderboom instead of landing at Richards Bay. Upon arrival at Wonderboom, the pilot selected the gear down; three green lights illuminated, though the "gear in-transit" warning light remained on. Prior to landing on Runway 29, the pilot shut down and feathered both engines in anticipation of another left main gear collapse. As expected, the left main gear collapsed on touchdown, causing the aircraft to veer left off the runway.
Damage and Injuries
The accident resulted in damage limited to the left wing and propeller. No injuries were sustained.
Probable Cause
The probable cause, as determined by the South African Civil Aviation Authority, is that the left main gear collapsed on landing because the side braces were not driven into the fully extended over-center position prior to landing. Metallurgical analysis of failed components revealed no pre-existing failures or defects; all failures occurred due to overload. It is believed that improper or poor rigging of the landing gear system prevented the bellcrank of the left gear from driving the side braces into the over-center position when the gear was selected down, leading to the collapse on landing.