Optimising aircraft wash intervals from maintenance records

Abstract

Washing aircraft is a routine maintenance chore that is intended to reduce corrosion damage by removing corrodents. However, this exercise incurs costs that are substantial when applied to a fleet. The United States Air Force (USAF) algorithm for setting wash intervals was based on an environmental severity index and an implied set of economic assumptions. A novel approach is described for setting the economically optimal wash interval based on maintenance records, an atmospheric corrosion model, explicit economic parameters and corrosivity measurements. The maintenance records required are the number of man hours applied to repairing corrosion related damage and the number of months since the last repair. The atmospheric corrosion model assumed a bilogarithmic or power law relationship between cumulative damage and exposure time. The economic parameters considered are the cost per wash, the cost of unavailability during a wash and the charge rate for maintenance manpower. It is assumed that atmospheric severity increases corrosion damage, whereas washing decreases it. This approach requires a measure of atmospheric corrosivity that is not restricted to any particular method as long as the processing of maintenance data and the prediction of the optimal wash interval uses the same method.