What is one major function of the APU during pre-flight operations?

The auxiliary power unit (APU) serves several critical functions during pre-flight operations, one of which is to provide electrical power. This is particularly important in the pre-flight phase when the aircraft systems need power to operate, allowing for essential operations like cockpit instrument checks, cabin conditioning, and powering avionics without relying on external ground power sources.

By supplying electrical power, the APU enables the aircraft to maintain functionality and prepare for departure while on the ground. This capability allows ground crews to perform necessary checks and systems tests without starting the main engines, which helps in conserving fuel and reducing noise during ground operations.

While starting the main engines is indeed another function that some may associate with the APU, it is not its primary role during pre-flight operations compared to its electrical power provision. The configuration of flight plan data and fueling processes are handled through different systems and procedures that do not involve the APU.