On August 28, 2019, about 2010 mountain daylight time, a Cessna 172, N53432, was substantially damaged when it was involved in an accident near Denver, Colorado. The student pilot received minor injuries. The airplane was operated as Title 14 Code of Federal Regulations Part 91 instructional flight.
The student pilot was conducting a solo cross-country flight. During the first leg of the flight, he noticed that the low voltage warning light illuminated intermittently and turned a faint red. He explained that although the voltmeter dropped from 28.5 volts (v) to 28.4v or 28.3v, it appeared to remain about 28v all the way to his destination, so he did not perceive a problem that required immediate action.
The student pilot conducted a touch-and-go landing at the destination airport and proceeded back to the departure airport. Shortly thereafter, the voltmeter “began to decline more.” The pilot requested visual flight rules flight following from air traffic control and climbed to about 10,000 ft. He reported that he was “not confident that he completely understood how an electrical system failure may affect the aircraft.” The voltmeter continued to indicate a loss of voltage as the pilot approached the departure airport. He reported the electrical issue to the tower controller, requested a straight-in approach, and was cleared to land on runway 03; at this time, the voltmeter indicated about 12v.
About 10 miles from the airport, the student pilot moved the flap selector to 10°; however, the airplane lost all electrical power, and the flaps did not extend. The student pilot reported that he had not previously completed a no-flap landing. The airplane crossed the runway numbers at 100 knots and touched down about the 1,000 ft. markings. The airplane bounced multiple times. The pilot applied brakes once the airplane remained on the ground but could not stop the airplane before it continued off the end of the runway and over a retaining wall, impacting a guardrail. The airplane sustained substantial damage to the propeller, fuselage, and landing gear.
The alternator was examined at the manufacturer’s facility with oversight from the Federal Aviation Administration. The alternator suffered impact damage to the pulley, cooling fins, and front housing. The damaged front housing was replaced with an exemplar unit and the alternator passed the acceptance test procedure for a new/rebuilt alternator. Some wiring was shipped with the alternator, including the aircraft-side connector and harness for the alternator control unit. The wiring from the alternator control unit displayed some insulation cracking and areas of exposed wires. It could not be determined whether this damage was the result of chafing or impact damage. The aircraft-side alternator control unit connector pin sockets were loose, with no apparent sealing or strain relief. Two wires displayed crimp splices, which remained intact when manipulated.