Incident Details
The pilot/owner of the airplane reported a low thumping noise during takeoff on several occasions, which he attributed to the landing gear. He flew to an airport where a mechanic familiar with the airplane attempted to troubleshoot the issue. After a visual inspection did not identify the problem, a test flight was conducted. During the flight, the mechanic, seated in the rear, heard the noise. After a few minutes of flying, the mechanic requested a return to the airport.
When the pilot extended the landing gear, the three green lights indicating gear down and locked did not illuminate. The pilot cycled the gear, but the lights again failed to illuminate. He stated that he believed he heard the appropriate sounds associated with proper gear extension and decided to continue the landing without attempting the manual gear extension as prescribed in the Emergency Procedures section of the pilot's operating handbook. During the landing roll, the landing gear collapsed.
Investigation Findings
Postaccident testing of the landing gear system was conducted with the airplane on jacks. Tests revealed that the battery charge was insufficient to fully extend the electrically operated landing gear. Further testing showed that the battery could accept a charge, but the alternator produced no output. Examination of the alternator revealed a defective rotor and excessively worn electrical brushes.