What happened
During the landing rollout, the main landing gear of the aircraft collapsed. The pilot reported that upon selecting the gear down position, the in-transit light illuminated and subsequently, all three landing gear position lights indicated the gear had extended. No gear warning indications or horns were heard during the initial extension.
The pilot performed a normal landing; however, before reaching the first taxiway, both main landing gear collapsed. During this collapse, the pilot noted that the in-transit light illuminated and the landing gear warning horn sounded. The three landing gear position lights remained illuminated after the aircraft came to rest.
The investigation
The aircraft was elevated for an operational test of the landing gear. During a normal gear extension sequence, the nose and right main landing gear functioned as designed. However, the left main landing gear extended only approximately 3/4 of the way before becoming mechanically bound. While the nose and right main gear position lights illuminated, the left main landing gear position light failed to illuminate during this binding event.
Upon further inspection, it was discovered that the left main landing gear could be forced into the down-and-locked position, at which point the gear position light would illuminate. The investigation found that corrosion on the linkage between the left oleo strut assembly and the gear, along with dirt present on the landing gear position switches, contributed to the malfunction. After the linkage was disconnected, the left main landing gear moved freely.