NTSB Identification: LAX04LA108.
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Accident occurred Sunday, January 18, 2004 in Tucson, AZ
Probable Cause Approval Date: 04/28/2005
Aircraft: Cessna P210N, registration: N4873K
Injuries: 1 Uninjured.

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 the landing roll, the airplane's left main landing gear collapsed and the airplane collided with a taxiway sign. While en route to his destination, the battery warning light illuminated, indicating that the electrical system was not charging. The pilot performed the emergency checklist items; however, the alternator would not reset. The pilot then reversed course to return to the departure airport. The pilot turned off all nonessential electrical equipment in an attempt to conserve battery power. The pilot extended the landing gear and 10 degrees of flaps, then turned the master switch off. The pilot later told responding airport police officers that he did not wait for the gear enunciator lights to turn green indicating that the landing gear was down-and-locked before shutting off the electrical master switch. As the airplane approached the airport, the pilot turned the master switch back on, but the battery had fully drained. The pilot said that he was unsure if the gear were down and locked so on final approach he pumped the emergency gear extension handle. During the landing roll, the left main gear collapsed. Post accident examination of the electrical system revealed that the main alternator field wire and power wire terminals were broken due to a vibration of the alternator. The alternator was not secure on its mounting bracket due to fretting on the forward portion of the alternator bracket housing, which had enlarged the holes into an oval shape. When the alternator and bracket were touched, the entire assembly would move.

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

the failure of the electrical charging system and pilot's failure to verify that the gear was down-and-locked prior to the complete electrical system failure.

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