What is one of the uses of gas turbine engines in aircraft besides propulsion?

Gas turbine engines play a crucial role in aircraft operations beyond just providing propulsion. One significant use is as an auxiliary power unit (APU). The APU is a smaller gas turbine engine that generates power for starting the main engines and supplies electrical power and compressed air for various functions within the aircraft when it is on the ground or during flight when the main engines are not operating at full capacity.

The APU allows for the operation of onboard systems, such as air conditioning, lighting, and avionics, without reliance on the main engines. This capability is especially useful during pre-flight procedures or when the aircraft is parked at the gate, ensuring the aircraft remains functional and comfortable for passengers and crew.

While steering control, instrument calibration, and flight stabilization are indeed critical components of aircraft operation, they do not directly hinge on the gas turbine engine's role in generating auxiliary power, highlighting the unique and essential function of the APU in the overall aircraft system.