What happened
During a night flight, the aircraft experienced a partial loss of electrical power while en-route. The pilot attempted to use the electrical system to extend the landing gear, but the gear failed to deploy. While established on a right downwind for the runway, the pilot performed a manual extension of the landing gear. However, the pilot did not receive the three green annunciator lights required to confirm that the landing gear was fully extended and locked.
Because radio communications were unavailable, air traffic control provided landing clearance using a steady green light gun signal. During the landing roll, the left main landing gear collapsed. This caused the aircraft to exit the runway and strike a runway sign. The aircraft then spun 180 degrees before coming to rest in an upright position.
Findings
The investigation found that the cause of the partial loss of electrical power was not determined.