Reno, NV, USA
N37KF
AEROVODOCHODY L-29 DELFIN
While being flown on an air race qualification/training flight, the experimental jet’s engine support mount, which had been recently installed to accommodate an increased-thrust engine modification, failed to keep the engine properly aligned. The resultant misalignment resulted in jet blast being directed onto and melting a portion of the rudder support structure. Although there was no indication of the problem in flight, during the landing roll, the pilot discovered that the rudder did not function properly, and directional control had to be maintained by alternate means. During the investigation, it was determined that five other racing airplanes of the same make and model had been modified in a similar manner and that there were slight structural variations and areas of poor welding associated with some of the mounts. As a result of this accident, the manufacturer of the engine modification instituted a program to obtain an independent professional engineering analysis of the engine mount design. Later, in response to another accident, the National Transportation Safety Board (NTSB) issued Safety Recommendation A-12-13, which asked the Reno Air Race Association (RARA) to require aircraft owners to provide an engineering evaluation for aircraft with any major modification. On August 27, 2012, pending receipt of further information showing that the process proposed by RARA specifically requires an owner of an aircraft with a major modification to provide an engineering evaluation that includes flight demonstrations and analysis within the anticipated flight envelope, the NTSB classified the recommendation Open-Acceptable Response.
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.
The failure of a modified engine mount to keep the engine properly aligned, which resulted in partial failure of the rudder support structure due to the deflection of the jet engine exhaust.
Source: NTSB Aviation Accident Database
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