MADISON, WI, USA
N611AW
British Aerospace BAE-146-300
While in cruise flight at 12,000 feet mean sea level, the no. 2 engine had a fire indication. The crew shut the engine down in flight and landed uneventfully. Investigation found a cracked left fuel manifold segment in the no. 2 engine. Metallurgical analysis established that the crack was characterized by fatigue striations, and that the crack occurred in a position on the manifold where there was an abrupt change in material thickness. There had been two previous occurrences of cracked manifolds reported by the operator and investigated by the NTSB. Prior to this incident, the manufacturer had taken three actions to resolve fuel manifold cracking; they were: 1.) introduce a redesign of manifold segments, 2.) agree to replace all operator manifold assemblies with the improved design, and 3.) introduce an eddy current inspection procedure for detecting manifold cracks. Following this incident, the FAA mandated more frequent inspection intervals and adoption of the new eddy-current inspection process for the unimproved manifolds.
HISTORY OF FLIGHT On January 27, 1995, about 1723 central standard time (CST), a British Aerospace, BAe 146-300, N611AW, experienced a fire warning light while in cruise flight near Madison, Wisconsin. The airplane, operated and maintained by Air Wisconsin Airlines as United Express flight 5329, was not damaged and landed at Dane County Regional-Truax Field, Madison, Wisconsin. The pilot, the first officer, two flight attendants, and 85 passengers were not injured. Instrument meteorological conditions prevailed and an instrument flight rules flight plan was filed for the scheduled domestic 14 CFR Part 121 passenger flight. The flight originated from Chicago O'Hare International Airport, Chicago, Illinois, at 1713 CST. The airplane was in cruise flight at 12,000 feet above mean sea level (msl) when the fire warning light and bell alarm for the no. 2 engine activated. The flight crew reports that they secured the engine, discharged the fire bottle, and landed without further incident. AIRCRAFT INFORMATION The airplane was powered by four Textron Lycoming (now AlliedSignal Inc.) ALF-502R-5 turbojet engines, which produce approximately 6,970 pounds of thrust each. TEST AND RESEARCH The engine was inspected and a possible crack in the no. 2 engine fuel manifold, P/N 2-163-620-35, S/N 157P was found. The manifold, consisting of two segments, was removed and shipped to the National Transportation Safety Board for examination at its materials laboratory. A fatigue crack that was approximately 0.4 inch in length was found in the fifth scallop from the top of the part (See attached NTSB Metallurgist's Factual Report No. 95-109). The crack had propagated from the right fuel manifold segment's inner diameter into a fuel passage. No manufacturing or material defects were found. According to the Federal Aviation Administration (FAA) Service Difficulties reports and data supplied by AlliedSignal, 15 incidents of manifold cracking were reported in the United States in the five-year period preceding this incident. Two previous in-flight shutdowns investigated by the NTSB were traced to the same failure. Their NTSB case identification numbers were CHI94IA134 on April 17, 1994, and CHI93IA312 on July 20, 1993. As shown in the attached Textron Lycoming service bulletin ALF 502R 73-8, Figure 1, dated February 27, 1991, the cracking was typically found at a point where the inner wall of the manifold makes a sudden change in material thickness. Specifically, this point is located in the fifth scallop shaped feature from the top of each segment. AlliedSignal has taken several actions to resolve this problem. In July 1992, a redesigned pair of manifold segments were introduced by attached Service Bulletin ALF502R 73-14 that eliminated the material thickness transition in the fifth scallop. AlliedSignal subsequently agreed to replace all existing Air Wisconsin manifold assemblies with the new and improved version beginning on or about June 1, 1994 at a rate of four shipsets per month. AlliedSignal also evaluated Air Wisconsin's liquid penetrant inspection process used to detect external cracks on the manifold segments. The evaluation occurred in July 1993, and revealed shortcomings that led to the development of a redundant eddy current inspection. This inspection was issued on December 18, 1995 as Allied Signal Eddy Current Inspection Procedure 21-9054 (attached). The FAA issued attached Airworthiness Directive (AD) 97-11-05, effective on July 28, 1997, which requires initial and repetitive on-wing eddy current or in-shop fluorescent penetrant inspection of the old model fuel manifold assemblies. These inspection requirements terminate when the new, improved design manifold assembly, P/N 2-163-650-37 and -38, is installed. ADDITIONAL INFORMATION The Air Wisconsin Reliability Manager was contacted on December 3, 1998, to determine the number of fuel manifold-related fires that had occurred since this incident (January 27, 1995). He pointed out that the entire Air Wisconsin fleet presently has the new improved manifold parts installed and that, according to his records, there have been no in-flight engine fires on Air Wisconsin BAe-146 aircraft since they installed the new manifold parts. The other operator of this aircraft and engine in the United States is Mesaba Aviation Inc. Mesaba's director of powerplant engineering stated in a telephone call on December 3, 1998, that Mesaba had experienced no instances of fuel manifold cracking since they began operating the airplane in May of 1997.
A fuel leak in the no. 2 engine left fuel manifold segment due to a design defect which led to a fatigue crack.
Source: NTSB Aviation Accident Database
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