NTSB Factual Report

On January 31, 2016, about 1100 central standard time, an Aeronca model O-58B single-engine airplane, N47185, was substantially damaged while landing at Bulverde Airpark (1T8), Bulverde, Texas. The commercial pilot and passenger were not injured. The airplane was registered to and operated by Assend Dragon Aviation, LLC under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight without a flight plan. Day visual meteorological conditions (VMC) prevailed at the time of the accident. The local area flight departed 1T8 at 1055.

According to the pilot, the accident occurred during the second full-stop landing to runway 16 (2,890 feet by 40 feet, asphalt). The pilot reported that following a normal touchdown, during the landing roll, the airplane suddenly veered to the left. The pilot corrected for the left swerve with the application of right rudder and brake. The airplane subsequently entered a right swerve. The pilot stated that the airplane did not respond to his application of left rudder and brake inputs. The pilot reported that there was a 15 foot descending embankment and trees situated off the right side of the runway. He stated that, in order to avoid a runway excursion, he lowered the left wing and intentionally ground looped the airplane to the right. The left wing contacted the runway surface during the ground loop.

At 1051, the automated surface observing system (ASOS) at the San Antonio International Airport (SAT), located about 12 miles south of the accident site, reported: wind 230 degrees at 4 knots, surface visibility 10 statute miles, few clouds at 2,000 feet above ground level, temperature 19 degrees Celsius, dew point 14 degrees Celsius, and an altimeter setting of 29.88 inches of mercury. The pilot reported that the wind condition had been light-and-variable during the accident flight.

A postaccident inspection revealed substantial damage to the left wing's forward and rear spars. An additional inspection revealed a fracture to the left main landing gear wheel casting. The wheel fracture was located along the inner bearing race shelf and resulted in the bearing being exposed. The left tire tread did not exhibit any abnormal wear or scuffing. The wheel had been cast in 1942, and the owner reported that the airplane had accumulated 3,520 hours since new, with 10 hours since the last inspection.

The fractured wheel was submitted to the National Transportation Safety Board (NTSB) Materials Laboratory for additional examination. The prepared laboratory report indicated that the bearing race flange had fractured circumferentially, as well as radially in two places. Further examination of the fracture surfaces revealed areas of fatigue that were the result of casting oxide imperfections that had developed under typical loading of the landing gear. The observed oxide imperfections would have been present since the wheel was cast. Additionally, the observed alternating fatigue and overstress features would be consistent with spectrum loading, typical of those experienced by a landing gear wheel. Ultimately, the wheel failed as a result of progressive fatigue cracking.

NTSB Probable Cause

The failure of the left main landing gear wheel casting due to fatigue, which resulted in a loss of directional control during the landing roll.