Can the C-5 APU operate silently?

The C-5 APU does indeed produce operational noise levels while functioning. This is primarily due to the mechanical processes involved in generating power and providing pneumatic and hydraulic support to the aircraft systems. The APU encompasses engines and additional components that create sound, making it impossible for it to operate completely silently.

Understanding the operational noise levels of the APU is crucial for ground operations, especially in noise-sensitive environments or during nighttime operations, where noise regulations might be more stringent. Recognizing that the APU is not designed to function without noise sets realistic expectations for its use and informs operational procedures as part of airport management and ground support logistics.