History of Flight
On August 22, 2013, at about 1050 mountain daylight time, a Cessna TU206F, registration N922MA, was substantially damaged during landing on runway 10L at Boise Air Terminal/Gowen Field (BOI), Boise, Idaho. The commercial pilot and the four passengers were uninjured. The backcountry charter flight was operated by McCall Air under 14 CFR Part 135. Visual meteorological conditions prevailed, and no flight plan was filed.
The pilot reported that he had flown to Wilson Bar USFS Airport (C48) in Dixie, Idaho, to pick up passengers and transport them to BOI. The landing and departure at C48 were uneventful. The approach and initial touchdown on runway 10L at BOI were also normal. However, when the pilot lowered the nose landing gear (NLG) to the runway, the airplane began to vibrate severely, and he lost directional control. The airplane veered left and came to a stop near the runway edge. The pilot secured the airplane and everyone exited safely.
Personnel Information
FAA records indicated the pilot held a commercial pilot certificate with airplane single- and multi-engine land ratings. He had approximately 6,837 total flight hours, including about 4,568 hours in the accident airplane make and model. His most recent flight review was in July 2013, and his most recent FAA second-class medical certificate was issued in May 2013.
Aircraft Information
The airplane was manufactured in 1976 and equipped with a Continental Motors TSIO-520 series engine. It had a total time in service of about 6,706 hours. The most recent inspection under the continuous inspection program was completed on August 6, 2013, and the airplane had flown about 52 hours since then.
Meteorological Information
The 1053 BOI automated weather observation reported wind from 160 degrees at 10 knots, visibility 10 miles, clear skies, temperature 31°C, dew point 8°C, and an altimeter setting of 29.99 inches of mercury.
Wreckage and Impact Information
The airplane came to rest upright with its NLG collapsed near the north edge of the runway, about 1,400 feet beyond the landing threshold. The outboard end of the right wing incurred scraping and buckling damage from contact with the runway. The NLG strut was folded aft under the fuselage, with the upper link of the torque assembly fracture-separated from the strut. The diagonal braces were fractured and/or gouged. No non-impact damage to the nose wheel steering mechanism was noted.
Additional Information
Nose Landing Gear Design
The NLG consists of a trunnion assembly affixed to the airframe, including the shock strut cylinder, two diagonal braces, steering actuator, and shimmy dampener. The shock strut assembly mates with the trunnion and includes the shock strut piston, fork, wheel, and tire. A torque link assembly controls rotation for nose wheel steering.
Nose Landing Gear Inspections and Maintenance
The operator used a manufacturer's continuous airworthiness inspection program. Most NLG components were original. The most recent NLG maintenance was on August 22, 2012, when the upper torque link and hardware were replaced. That component had about 352 hours in service at the time of the accident. Cessna Supplemental Inspection (SI) 32-20-01, applicable to the accident airplane, required inspections every 3,000 hours or 5 years to ensure structural integrity of nose gear components. The operator reported accomplishing the SI at least twice, most recently on August 22, 2012, well within intervals.
Nose Landing Gear Laboratory Examination
The NLG components were examined at the Cessna Materials and Process Engineering laboratory in July and September 2015. All components were proper parts; hardware was present. The shimmy dampener functioned normally. Two lugs on the steering collar had fractured in ductile overload, with no pre-existing damage. However, a paint shadow on one lug suggested the presence of an object near the bolt hole at the time of painting, but its significance could not be determined. A crack was found on the steering collar's upper circumference, identified as high-cycle fatigue, but its age could not be determined. The roller bearing between the collar and strut did not rotate freely and exhibited light corrosion, indicating insufficient lubrication.
Nose Gear Shimmy
The FAA Aviation Maintenance Technician Handbook defines shimmy as abnormal vibration of the nose wheel, often caused by looseness or imbalance. Shimmy, if uncorrected, can damage components and lead to failure. The accident-induced damage precluded assessment of the NLG's condition regarding shimmy susceptibility. The pilot reported no previous shimmy problems.