Synopsis
On April 24, 2008, at 1710 Mountain Daylight Time, a twin-engine Cessna 421C, N513FS, sustained substantial damage after veering off the runway during landing roll-out at Sterling Municipal Airport (STK), Sterling, Colorado. The airline transport pilot and the two passengers were not injured. The airplane was registered to and operated by Alpine Air LLC, Telluride, Colorado. A visual flight rules flight plan was filed for the flight that departed City of Colorado Springs Municipal Airport at 1630 and was destined for Sterling. Visual meteorological conditions prevailed for the on-demand, nonscheduled flight conducted under 14 Code of Federal Regulations Part 135.
Pilot Report
In a written statement, the pilot reported that he continuously monitored weather conditions prior to landing on Runway 33. He made a normal landing and the wind felt like it was blowing right down the runway. As he decelerated through an estimated 50-60 knots, an extreme gust of wind, estimated at least 50 knots, hit the aircraft from the right side. The aircraft weathervaned into the wind, and the pilot applied full left rudder to compensate, but the input was not effective. The pilot attempted to maintain control as the airplane skipped off the right side of the runway onto the grass. Subsequently, the left main landing gear collapsed due to side load, and the aircraft came to an immediate stop. The pilot secured the airplane and evacuated the two passengers.
Examination Findings
Several Federal Aviation Administration safety inspectors performed an on-scene examination. The nose gear had collapsed and the left main gear had separated from the airframe. The right main landing gear remained attached, but the upper and lower torque links had separated, and the wheel was rotated to the right. Examination of the upper and lower link assembly's securing bolt, bushing, two AN washers, castellated nut, and cotter pin revealed that it had pulled through the lower torque link boss, allowing the main wheel, brake, and strut assembly to rotate inside the strut housing. Both propellers were damaged, and the left wing sustained substantial damage.
Maintenance History
The airplane was last inspected on March 13, 2008, in accordance with the Cessna 421C progressive care operation 3 &4 checklists at an airframe total time of 6,791.9 hours. The logged entry stated, "Adjusted main gear camber and toe." The accident occurred approximately 39.1 hours after this inspection.
On November 23, 1983, Cessna issued Service Kit SK 421-118, which called for replacement of washers and inspection of the main gear torque links. The Service Kit specified washer P/N 504518-2 to be installed under the bolt head and nut, with replacement washer P/N S1450-5H12-063 to be incorporated into the next revision. Cessna issued a Service Information Letter in conjunction with the Service Kit for "improved service life and main gear alignment retention." The washers listed in the Service Kit were not installed on the accident airplane. Compliance with the Service Kit and Service Information Letter is not mandatory.
Pilot Information
The pilot held an airline transport pilot rating for airplane multi-engine land and instrument airplane. He reported a total of 8,720 flight hours, of which 557 hours were in a Cessna 421C.
Weather Conditions
Weather reported at Sterling Municipal Airport at 1653 included variable wind at 5 knots gusting to 14 knots, visibility 10 miles, scattered clouds at 6,000 feet, overcast clouds at 10,000 feet, temperature 63 degrees Fahrenheit, dewpoint 33 degrees Fahrenheit, and barometric pressure 29.71 inches. Remarks indicated a wind shift at 1614, a peak wind from 310 degrees at 32 knots recorded at 1625, and lightning east of the airport.