NTSB Identification: LAX99LA221.
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Accident occurred Sunday, June 20, 1999 in SAN DIEGO, CA
Probable Cause Approval Date: 08/16/2001
Aircraft: Cessna 172M, registration: N61560
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

During a practice instrument approach on a dark night, the aircraft began losing electrical power. The airplane was over a low cloud layer and the pilot cancelled his IFR clearance, informed ATC that he was losing electrical power and that he would fly back to home base under visual flight rules. He then flew in a southerly direction, following roads until he decided that he had flown far enough to locate his home airport. He was unable to locate the airport, made a 180-degree turn in an attempt to locate another airport, and found that he was unsure of his position. He elected to land on a large well-lit parking lot and collided with concrete barriers during the landing roll. An automotive alternator was found installed on the airplane, with a nonapproved support bracket that allowed for pulley misalignment, slack belt tension, and excessive vibration. The voltage regulator, alternator, and associated wiring harnesses were removed for functional testing. The voltage regulator and the alternator as separate units passed functional tests. The power input connector on the regulator fit loosely and allowed an intermittent electrical connection. Failure of the connection would allow the alternator to cease operating. A month prior to the accident, in response to pilot reports of intermittent low system output, a mechanic removed the alternator for repair. The automotive shop that performed the work found the unit had an acceptable voltage output, but the amperage was low. A diode in the bridge rectifier was replaced and the mechanic reinstalled the alternator on the engine. The mechanic said the alternator had been on the airplane for several years and 'it never occurred to [him] to check the Type Certificate Data Sheet' to ensure the alternator was approved for airplanes.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The mechanic's improper installation of nonapproved automotive electrical system parts, and his failure to ensure that all electrical connections were secure during the reinstallation, which resulted in the failure of the electrical system. The pilot's becoming lost and disoriented during the subsequent attempt to find an airport on the dark night flight was a factor.

Full narrative available

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