Accident Summary
On July 18, 2016, about 1230 Alaska daylight time, a tailwheel-equipped Stinson 108 airplane, registration N343C, sustained substantial damage following a loss of control during the landing rollout at Haines Airport, Haines, Alaska. The certificated private pilot and three passengers were not injured. The airplane was registered to and operated by the pilot as a visual flight rules personal flight under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight departed Skagway Airport (SGY) at about 1200, destined for Haines Airport (HNS).
Pilot and Passenger Statements
The pilot reported that he listened to the automated weather at HNS prior to arrival and elected to land on runway 26 with a quartering tailwind because the winds were light and variable. He performed a normal wheel landing. During the rollout at about 20 mph, he initiated a right turn toward taxiway B, a high-speed exit taxiway. As he turned, the airplane abruptly turned right, resulting in a 180° right ground loop. He applied full left rudder and left brake, but the right turn continued. The left main landing gear collapsed, and the fuselage and left wing impacted the runway surface. Substantial damage occurred to the left wing, aileron, lift strut, and lower fuselage. The pilot noted that after the accident, the winds were stronger and gusting from various directions.
A passenger seated in the front right seat stated that during the approach he heard the automated weather report wind at 4 knots but could not recall the direction. The landing felt normal until near the end of the landing roll, when the airplane made an unexpected abrupt right turn and then collapsed onto its left side during the ground loop. After the accident, he noticed gusting winds.
Post-Accident Examination
Photographs revealed metal scrapes on the runway surface collocated with rubber wheel skid marks from the left main landing gear wheel. The ground scars began about 50 feet before the tight ground loop signatures. The left main landing gear wheel assembly separated from the left main landing gear leg at the axle weld and came to rest about 15 feet behind the wreckage. The left main landing gear leg separated from the fuselage near the upper shock strut attachment points. No tailwheel abnormalities were observed at the accident scene. The airplane was towed to a hangar on the right main landing gear wheel and tailwheel.
During a post-accident examination after recovery, the pilot discovered that the airframe tailwheel assembly attachment mount was fractured through its entire width. This bracket is one of two airframe attachment points for the tailwheel assembly. The tailwheel attachment mount and left main landing gear wheel hub and axle were sent to the NTSB Materials Laboratory for detailed examinations.
An NTSB materials engineer conducted a detailed examination of the fractured tailwheel assembly. Features consistent with corrosion intermixed with overstress failure were present at the bracket weld. The fractured surface of the left wheel axle was also examined. Features on this fracture surface were generally consistent with tensile overstress, such as microscopic dimple ruptures. The wheel axle also exhibited some areas with intergranular fracture and irregular weld material. A Materials Laboratory Factual Report is included in the public docket.
Aircraft and Pilot Information
The airplane had a total time of 3,305 hours, and an annual inspection had been completed on August 14, 2015. The pilot stated that the landing weight was estimated at 2,200 lbs, which was 30 lbs under the maximum gross weight limit. The pilot originally stated the landing weight at 2,240 lbs on the NTSB form but later changed it via email.
The pilot had logged about 1,001 total flight hours and 900 hours of pilot-in-command time in the accident airplane. His last biennial flight review was conducted in the accident airplane on March 29, 2016.
Weather Conditions
The closest weather reporting facility was HNS. At 1154, a METAR reported wind from 150° at 3 knots, sky clear, visibility 10 statute miles, temperature 70°F, dew point 57°F, and barometric pressure 29.90 inches of mercury.