An Assessment of the Economic Viability of Engine Wash Procedures on the Lifecycle Costs of an Aircraft Fleet.
Authors: Wehrspohn Jennifer , Pohya Ahmad Ali , Wicke Kai 
Published: February 2024

Aircraft operators find themselves in a highly complex and competitive environment in which the economic pressure on companies is constantly increasing. In addition, annual air traffic is expected to increase by 4-5% (despite the Covid-19 pandemic), which requires significant improvements of aircraft efficiency. To address this on European and global scale, long-term economic and ecologic goals have been defined in the "Flightpath 2050" by the European Commission. One way to reduce both operating costs and environmental impact is to reduce aircraft fuel consumption. Regularly performed engine washes can reduce the accumulation of dirt and debris in the engine and partially restore the performance degradation as well as lower the wear and tear of the engine. This results in lower exhaust gas temperature and a slower aging engine with longer intervals between required maintenance events.

Most engine wash studies have drawn their system boundary around the engine and consider only the one-time improvements that result from a wash. Long term effects that build on these improvements, such as changes in maintenance and replacement cycles, are usually not considered. Few studies are available that extend their system boundary and consider changes in maintenance costs. Yet the value of engine wash processes is often quantified on an insufficient setting, especially when environmental conditions and fleet effects are neglected. To estimate the overall benefit and assess the impact on lifecycle costs, a full evaluation of engine wash within an entire fleet is required and fleet effects such as the possibility of downrating the engine for a smaller aircraft should be considered.

The aim of this work is to quantify the true value of engine wash procedures considering both physical constraints as well as operational fleet wide considerations. Using discrete event simulations at fleet level, a detailed investigation of the primary and secondary effects and a quantification of lifecycle costs will be performed. Particular attention will be paid to the influence on maintenance costs as well as the economic effect of increased time on wing. With the help of an improved environmental modeling and with the consideration of fleet effects, a holistic statement is possible.

To investigate this problem, a lifecycle costing method, named LYFE, developed by DLR will be used. LYFE uses discrete event simulation to model the product lifecycle from order to operation until disposal of an aircraft fleet. For this analysis the tool will be extended to separate the lifecycles of the engines and those of the aircraft, so the engines can change the aircraft and the downrating of the engine for a smaller aircraft can be modeled. In order to represent the contamination and the performance degradation of the engines as realistically as possible, data on the outside air temperature, dust, pollution and other particles in certain regions at the various airports are also included in the tool. Furthermore, the option of derating the engine’s thrust is considered. The lifecycle of two different fleets will be simulated and studied. The difference between the two fleets is that the baseline fleet does not perform any engine washes, while the study fleet performs engine washes. Both fleets consist of different types of aircraft, so that downrating of the engines is possible and the entire lifecycles of the aircraft can be mapped. The evaluation follows two approaches: firstly, the engine wash is carried out and examined regularly; secondly, the intervals at which the engine wash is carried out are optimized in such a way that the lifecycle costs of the fleet are as low as possible. In both cases the number of engines necessary to operate the fleet will be the basis for an overall statement.

With this holistic view of how engine washes within a fleet affect its lifecycle costs, a much more realistic statement about this on-wing maintenance action is possible.