Crescent City, CA, USA
N26533
Cessna 421C
The right main landing gear scissors separated during the landing roll, resulting in a ground loop and the collapse of the right main landing gear. Post accident examination of the right landing gear scissors assembly revealed that a hinge bolt assembly had failed. Recent maintenance had reportedly been performed on both main landing gears. A Cessna Service Information Letter, ME83-37, dated November 23, 1983, recommended main landing gear scissor washer replacement for airplanes with serial numbers that included the accident airplane. The Service Letter recommended replacement of the two outer washers on the main landing gear scissor link for improved service life, and main gear wheel alignment retension. The Service Letter called for the installation of a new AN175-20 scissor bolt, and one 5045018-2 washer under the head of the bolt for each main landing gear scissors. Post accident examination of the scissor assembly revealed two damaged washers under the head of the scissors bolt, with diameters only slightly larger than the extreme hex points of the bolt head. The two washers were significantly smaller than the recommended washers, and were extruded, or bent towards, the scissor bolt head, which allowed the upper and lower scissor assembly to disconnect.
On March 4, 2003, at 2245 Pacific standard time, a Cessna 421C, N26533, veered off the runway and ground looped while landing at the Crescent City, California, airport. The airplane was operated by Westlog, Inc., d.b.a., Cal-Ore Life Flight as a positioning flight under 14 CFR Part 91. The airline transport pilot and two passengers were not injured. The airplane was substantially damaged. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight originated at Medford, Oregon, at an undetermined time. Post accident examination of the right landing gear retract scissors assembly revealed that a hinge bolt assembly had failed. The parts were recovered by Federal Aviation Administration inspectors for detailed examination of the hardware and the maintenance manual. Recent maintenance had reportedly been performed on both main landing gears. A Cessna Service Information Letter ME83-37, dated November 23, 1983, recommended main landing gear scissor washer replacement for Cessna models 401 thru 421, with serial numbers that included the accident airplane. The purpose was to recommend replacement of the two outer washers on the main landing gear scissor link for improved service life and main gear wheel alignment retension. A Cessna Service Kit SK421-118, provided the necessary parts to comply with ME83-37. Step 3.b calls for the installation of a new AN175-20 scissor bolt and one 5045018-2 washer under the head of the bolt for each main landing gear scissors. The 5045018-2, 0.75-inch diameter washer is 0.063-inch thick and made of SAE 4130 steel with an inside diameter of 0.313-inch, with a tolerance of +0.031-inch and minus zero. The AN 175-20 scissors bolt is 0.3125-inch outside diameter. Post accident examination of the scissor assembly revealed two damaged washers under the head of the scissors bolt with diameters only slightly more than the extreme hex points of the bolt head, measuring about 0.564-inch. One washer internal diameter was about 0.453-inch and 0.024-inch thick; the other internal diameter was about 0.325-inch and about 0.032-inch thick. The washer material appears to be stainless steel. The two washers were extruded, or bent towards the scissor bolt head, allowing for the upper and lower scissor assembly to disconnect.
The separation of the upper and lower right main landing gear scissor links due to improper maintenance, which resulted in a ground loop, and the collapse of the right main landing gear during the landing roll.
Source: NTSB Aviation Accident Database
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