Overhaul Life Development and Early Failure Detection of Aircraft Gas Turbines

Abstract

In a modern gas turbine‐powered aircraft, engine material cost is the major single contributor to direct maintenance and overhaul cost. Due to the large expenditures involved, even a small percentage improvement in this field will result in the achievement of large savings. By concentrating on the reduction of both scheduled and unscheduled removals, this cost can be minimized. An analysis of the experience gained with the application (o gas turbine engines, of traditional overhaul life development programmes shows that these are of no benefit in determining the limitations of the engine. Experience and control of the total time or take‐off cycles of components, rather than time between overhaul, is the most important factor in the operational development of gas turbine engines. Overhaul life development can be divided into two phases: the initial programme applied to new engines with little operational background, and the developed programme applied to engines with substantial operating experience. In the initial programme, the sampling of two engines every 100 hours from a declared plateau can provide the required information and produces the required stagger in total time of components. In the developed programme large steps in overhaul life can be declared without further sampling. Life development of critical engine components cannot be done in service and requires manufacturer's cyclic testing ahead of airline experience until fail‐safe designs are achieved. Early failure detection of gas turbine engines is a Held of great potential return which to date has been only barely explored. Both engine manufacturers and operators need to develop tools and techniques for effective early failure detection quickly, to gain the large benefits which this field offers. Examples of the application of some early failure detection designs and techniques in Trans‐Canada Air Lines (T.C.A.) are given. These are in the field of visual examination with increased access to the engine, X‐ray examination of flame tubes with the engine installed in the aircraft, more effective use of the oil system to give warning of failure, engine vibration monitoring and automatic flight performance recording.