What happened
Tower controllers notified the pilot that they observed smoke trailing from the right engine shortly after takeoff. The pilot elected to return to the field for an emergency landing. During the approach, the pilot lowered the landing gear and verified the gear down indications on the instrument panel.
Upon touchdown, the landing gear collapsed during the landing roll. The aircraft was subsequently recovered and placed on jacks for inspection.
The investigation
A mechanical examination of the recovered airplane revealed that the landing gear safety switch had been contaminated with water. The component was found to be corroded and improperly rigged, which likely prevented proper operation of the gear indication system or the gear locking mechanism.
Findings
The collapse of the landing gear was directly linked to the condition of the safety switch. The contamination and corrosion compromised the integrity of the switch, leading to improper rigging. This mechanical failure contributed to the inability of the landing gear to support the aircraft during the landing roll.