Airfleet maintenance case study

Abstract

Nowadays, aircraft operators are trying to minimise their expenses. Most of the cost for an aircraft operator is allocated to the engine maintenance overhaul. Therefore, each shop visit should be as efficient as possible taking into account both life and non-life limited parts. This thesis attempts to analyse the influence of a typical maintenance program to the lifing of non-life limited parts. A Boeing 777-200ER equipped with a General Electric GE90-94B engine was selected for this project. Turbomatch and Hermes models were used to simulate the operation of both engine and aircraft over a variety of operating conditions. In addition, a reference flight for this type of long haul aircraft was simulated. Next step was the creation of the maintenance program for such an engine. In order to predict the interval and the cost for each engine shop visit, cost estimate relationships had to be created. A regression process enabled the author to create five cost estimate relationships, which can be used to predict a basic maintenance program for the GE90-94B. The thesis progresses with the non-life limited parts lifing study and more specifically it focuses on the high pressure compressor blades. A preliminary compressor design as well as, a detailed analysis of the first stage rotor blades were conducted, revealing the stresses imposed on the blade surface. The next step involved a fracture mechanics analysis for the blades. By using an Advisory Circular issued by the Federal Aviation Administration and a fracture mechanics model the author was able to estimate the probability for a blade to develop a 1mm length crack over a specific amount of flight cycles. Finally, a Double Goodman Diagram analysis was performed to evaluate the effect of the combine low and high fatigue on the blades.