Reliability analysis of the electrical system in Boeing 757-200 aircraft and RB211-535 engines
Air travel is today one of safest mode of transport. High reliability requirements have been established in the aviation industry because of the potentially severe consequences of system failure. In 1953, twin-engine aircraft were restricted to fly on routes that were within 60 minutes from an alternate airport. In 1985 the Extended Twin-engine Operations (ETOPS) rules were established. They are a deviation from the 60 minute restriction, allowing twin-engine aircraft to fly further away from an alternative airport, if operators can fulfill certain technical and operational requirements. To obtain ETOPS approval both the aircraft and the operator have to comply with a set of standards and regulations [1], [2]. The electrical system in Boeing 757-200 is a large and a complex system. The consequences of losing all electrical power in-flight can cause, in worst case scenario, catastrophic accidents. Because of the severity of such failures, a fail-safe redundancy is built into the electrical system. The Boeing 757-200 was designed both with three and four generators. Aircrafts with four generators have Hydraulic motor generator (HMG) added as the fourth generator. The Boeing 757-200 aircraft with three generators is today non-ETOPS, whereas an aircraft with four generators has ETOPS approval up to certain limits. The main objective of this research project is to develop a quantitative method for determining the reliability of the electrical system in Boeing 757-200 aircraft with three generators and the reliability of the RB211-535 engines. This is done to assess whether the electrical system in question meets the reliability requirements for 120 minutes ETOPS approval, without an additional generator. The reliability modeling of this research project is based on the Reliability Block Diagram technique and the commercial software tool, BlockSim 10, is used to construct a model of the systems with the RBD approach. Analyses will be performed both analytically and via simulation using the BlockSim software, where the software undertakes all computations. These results are promising and support the idea that it is a viable option to apply for a 120 minute ETOPS approval, although the electrical system only contains three generators. Keywords: Boeing 757-200 electrical system, RB211-535 engines, Extended operation (ETOPS) and Regulations, Reliability, Reliability Block Diagram.
Rekstrarverkfræði, Flugöryggi, Rafkerfi farartækja, Tækni- og verkfræðideild, Meistaraprófsritgerðir, Engineering management, Air traffic control, Reliability, School of Science and Engineering
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