N37KF

On June 18, 2011, about 1450 Pacific daylight time, an experimental Aerovodochody L-29 Delfin, N37KF, experienced the partial failure of the primary airframe structure supporting the airplane's rudder while in the air race pattern at Reno-Stead Airport, Reno, Nevada. The commercial pilot, who was the sole occupant, was not injured, but the airplane, which was owned and operated by Raju Mann Ward, sustained substantial damage. The local 14 Code of Federal Regulations Part 91 air race qualification/training flight, which took off from the same airport about 20 minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed.

According to the Federal Aviation Administration (FAA) inspector who responded to the scene, while the airplane was in flight, part of the engine support structure that had been installed as part of a modification to install a higher thrust engine, had failed to hold the new engine in proper alignment. That failure allowed jet blast from the engine to be deflected onto a portion of the primary airframe structure. The melting of that structure affected the support and movement of the airplane's rudder. Although the failure occurred in flight, it was not detected until the pilot was operating the rudder pedals during the landing roll. Although the pilot was able to keep the airplane on the runway, she had to apply alternative/non-standard control inputs in order to do so.

During the investigation it was determined that at least five other L-29 airplanes had the same type of mounts, which were all designed, welded/manufactured by the same entity. According to the FAA inspector who looked at these mounts, the welding was poor on some of them, and there was some degree of structural variation between a number of the mounts.