Accident Overview
On September 16, 2016, about 0820 Alaska daylight time, a tundra tire-equipped Helio Courier H-295, registration N6464V, sustained substantial damage following a loss of control and subsequent runway excursion during takeoff from an unimproved airstrip near Fairbanks, Alaska. The aircraft was operated by Wright Air Service under 14 CFR Part 135 as a VFR on-demand commercial flight. The airline transport pilot and one passenger were not injured. Visual meteorological conditions prevailed, and a VFR flight plan was filed.
Pilot Account
During an interview on September 20, the pilot reported that the takeoff began normally. Approximately 300 feet into the takeoff roll, the airplane veered sharply to the left, exited the airstrip, and impacted brush and trees, resulting in substantial damage to the fuselage and left horizontal stabilator.
Post-Accident Examination
Examination revealed that the tailwheel had separated from its attach point and folded beneath the empennage. A trench was observed in the airstrip surface starting about 300 feet from the takeoff initiation point and continuing to the impact location. The tailwheel A-frame consisted of two arms extending forward from a flanged downtube, with a brace cross tube between the forward-facing arms. The A-frame was attached to the airframe at the forward ends of the arms and to a shock absorber on the aft side of the downtube. The corner brace between the left arm and downtube was buckled and cracked, and the left arm was fractured at its weld to the downtube.
Materials Laboratory Findings
The tailwheel A-frame assembly was examined at the NTSB Materials Laboratory. Visual and magnified optical examinations of the left arm fracture revealed a matte gray surface on slant planes, consistent with ductile overstress fracture. However, a portion of the fracture surface was perpendicular to the surface across most of the fracture, with small shear lips. Two areas had no shear lips and were oxidized with smooth curving boundaries, consistent with fatigue. The right arm had a crack opened in the lab; examination showed a portion of the fracture surface on the upper side was perpendicular, oxidized, and displayed curving black arrest lines, features consistent with fatigue. The remainder had matte gray features on slant planes. The fatigue regions in the left and right arms were up to 0.016 inch and 0.066 inch deep, respectively. The brace tube separation from the right arm and the shock absorber attachment ear fracture both exhibited features consistent with ductile overstress fracture.
Weather Conditions
The nearest weather reporting station was Fairbanks International Airport, about 42 miles south. At 0753, a METAR reported wind from 050° at 4 knots, visibility 10 statute miles, broken clouds at 5,500, 7,500, and 15,000 feet, temperature 39°F, dew point 37°F, altimeter 29.36 inHg.