An Optional APU for Passenger Aircraft

Abstract

Most passenger aircraft do not need an Auxiliary Power Unit (APU) to provide them with extra electric, pneumatic, and hydraulic power. Nevertheless they are equipped with one, although use of the APU at airports gets restricted more and more. It is proposed here to offer the APU only as an option. The hypothesis of this research is that an aircraft type with an optional APU (with the option not selected when the aircraft is ordered) has economical and ecological advantages in operation compared to an aircraft not offering an opt-out from the APU. Others have only looked at replacing the gas turbine based APU of today with some other device and have mostly increased mass and costs with their proposal. However, eliminating the APU will clearly reduce mass and costs. Literature and the Internet was reviewed and simple calculations were made. It was found that ordering APU-like services from the airport (electric supply, conditioned air supply, engine start with air starter unit) tends to be more costly due to the need for additional labor. As long as it is still allowed to operate the noisy and polluting APUs at airports, a financial benefit can be obtained from an aircraft without an APU only for long range flights where APU mass is replaced by additional payload.