NTSB Factual Report

On January 18, 2004, at 0552 mountain standard time, a Cessna P210N, N4873K, experienced a collapse of the left main landing gear during the landing roll at the Tucson International Airport (TUS), Tucson, Arizona. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot was not injured; the airplane sustained substantial damage. The flight departed Tucson at 0440, en route to Dallas Love Field (DAL), Dallas, Texas. Visual meteorological conditions prevailed, and no flight plan had been filed.

The Tucson Airport Police interviewed the pilot immediately following the accident. He reported that en route, a light illuminated indicating that the battery was not charging. The pilot competed the emergency checklist procedures, but the light continued to illuminate. After lowering the landing gear and the flaps, the pilot turned the master switch to the "OFF" position, in order to conserve power. He did not wait for the "green light," indicating that the gear was in a down and locked position. The pilot landed without difficulty. However, during the landing roll, the right main gear collapsed, and the airplane collided with a taxiway sign.

The pilot submitted a written statement. While en route to Dallas, 30 miles east of Benson, Arizona, the low battery light illuminated. He verified that the alternator was not working and it would not reset. He turned the airplane in the direction of Tucson and declined landing at Benson because he had not landed there before. He advised Tucson approach control of his intentions and then turned the master switch into the "OFF" position. He continued to Tucson at an altitude of 17,500 feet mean sea level (msl). During a descent to 15,000 feet msl, the landing gear was lowered as the pilot searched for the airport. He again turned the radio master switch on and the global positioning system (GPS) indicated he was flying over the runways.

The Tucson International Air Traffic Control Tower (ATCT) advised him to fly heading 140; he turned and located runway 11L. He then extended the flaps and all electrical power was lost. The airplane was positioned on final for runway 11L and a 360-degree turn was completed because the airplane's altitude was too high. As the pilot turned onto final, the emergency gear extension lever was "pumped a few times" until he was certain the gear was fully extended. The airplane touched down at 70 knots. During the landing roll, the left main gear collapsed.

The electrical system was examined at Premier Aviation on February 25, 2004, under the auspices of a Federal Aviation Administration (FAA) inspector. The alternator, although it appeared securely attached, would move when it was touched. The technician reported that a 9-inch bolt secured the alternator to the engine mount by a bracket. A shorter bolt assisted in tensioning the alternator belt. Each of the bolts was secured in their respective positions. The longer bolt fit through the alternator housing and was clamped through the use of bushings. Although the longer bolt was torqued against the bushings, it was not secure in the housing due to aluminum wear on the forward portion of the housing. The forward portion of the housing was an oval shape. A vibration resulted, and the field and main power wires' terminals became disconnected. The tension of the alternator belt was normal.

On March 26, 2004, the bolts, bushings, and housing were reexamined. The housing diameter was measured at 0.8777-inch. The bolt diameter was measured to be 0.4373-inch. The bushings on the aft portion of the bolt housing measured 0.7468-inch for the outer diameter and 0.4601-inch for the inner diameter. The forward bushing inner diameter measured 0.5287-inch. The forward bushing was egg shaped and stuck in the bolt housing. Fretting corrosion was present along the surface of the forward housing.

ASA Dictionary of Aeronautical Terms defines fretting corrosion as a form of corrosion between two surfaces which have a slight amount of relative motion between them. The protective oxide coating that forms on aluminum or magnesium alloys is rubbed away by the movement of the parts. New oxides must be continually formed to replace those that are worn away.

NTSB Probable Cause

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.