Turbofan engine maintenance cost estimation for preliminary aircraft design : empirical regression with thrust and flight-cycle length

Abstract

An empirical preliminary-design equation is derived for planned turbofan engine maintenance reserve as a function of rated take-off thrust, T and flight-cycle length, L = EFH/EFC. 35 published maintenance cost observations are normalized to 2025 USD with the U.S. Consumer Price Index for All Urban Consumers (CPI-U) and fitted separately for small/medium and large engines. The recommended model is piecewise linear of the form C = a + b T + d/L. Power-law relations are discussed as sensitivity checks. The text documents calibration limits, source traceability, specific maintenance cost per rated thrust, C/T, and an example of a four-versus-two-engine comparison. Application to preliminary aircraft design is demonstrated by engine-number trades at constant total installed thrust, including four-versus-two-engine examples and a discussion of the limits of extending the approach towards distributed propulsion.