Flight Events
During flight, the pilot encountered an overvoltage condition and subsequently turned off the electrical master switch. The pilot noted that the VHF radio circuit breaker had tripped and that the turn and bank indicator emitted smoke. Approximately 10 miles from the airport, the pilot turned the master switch back on and attempted to reset the circuit breaker, but again observed smoke in the cockpit.
The pilot reported that the landing gear extended very rapidly and forcefully, but it did not lock into place. When the pilot attempted to follow the emergency gear extension procedure, the crank did not function. During landing, the main gear collapsed.
Examination Findings
An examination of the electrical system disclosed a charred and expanded battery. The down limit switch for the landing gear motor had broken from its mount, caused by the upper bell crank traveling beyond the down limit. A teardown of the landing gear actuator assembly revealed evidence of overtravel. The alternators, voltage regulators, and overvoltage relay all tested within allowable limits.