Primary finding
Probable cause
The failed retaining bolt and cracked backing plate, which resulted in a shift of the brake lining to contact the brake drum and a subsequent wheel lock when the brakes were applied.
Investigator assessment
Analysis narrative
The airline transport pilot had performed three touch-and-go maneuvers without braking. On the fourth and last planned landing roll about 30 mph, the airplane experienced an excessive tailwheel shimmy. About 25 mph, the airplane nosed over and came to rest inverted. Postaccident examination of the airplane revealed that the left main wheel/brake assembly was locked; thus, the wheel/tire could not be rotated. Partial disassembly of the wheel/brake assembly revealed a failed retaining bolt for the brake backing plate and a crack in the backing plate. The bolt likely broke off and became lodged in the assembly; thus, it is likely the failed retaining bolt and cracked backing plate resulted in a shift of the brake lining to contact the brake drum and led to a subsequent wheel lock when the brakes were applied.
Source record
Factual narrative
On August 30, 2018, about 1900 central daylight time, a Stearman A75N1 (PT17) airplane, sustained substantial damage when nosed over during the landing roll at the Kenosha Regional Airport (ENW), Kenosha, Wisconsin. The airline transport pilot, who was the sole occupant, was not injured, and the airplane sustained substantial damage to the rudder. The airplane was registered to and operated by a private individual as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed at the time of the accident, and a flight plan was not filed. The local flight departed ENW about 1830. According to the pilot, he had performed three touch and go maneuvers without the use of any braking. On the fourth and last planned landing roll out about 30 mph, the airplane experienced an excessive tail wheel shimmy due to a left brake assembly issue. About 25 mph, the airplane nosed over and came to rest inverted. Postaccident examination of the airplane by a Federal Aviation Administration inspector revealed the left main wheel/brake assembly was locked, and the wheel/tire could not be rotated. Partial disassembly of the wheel/brake assembly revealed a failed retaining bolt for the brake backing plate, and a crack in the backing plate. The pilot reported the specified brake lining to drum clearance was .008/.010 inches. The most recent annual inspection was completed on September 1, 2017, about 20 hours prior to the accident.