How are bleed air leaks detected and mitigated around the APU?

• A. Visual inspection only; no system checks required.
• B. Pressure/flow sensors detect leaks; validation through system checks; isolation valves and, if needed, APU shutdown and fire procedures.
• C. Bleed air leaks are not a concern for APU operations.
• D. Leaks are detected by smell only.

Answer: (B)

Bleed air leak detection around the APU relies on monitoring the bleed air system with pressure and flow sensors. When the system is supplying bleed air, a leak shows up as an abnormal drop in pressure or an unexpected change in flow in the bleed lines. The fault management logic cross-checks sensor readings to confirm a leak rather than a transient fluctuation. Once a leak is validated, isolation valves are used to shut off the APU bleed from the rest of the system to prevent the leak from affecting other air systems and to preserve remaining bleed air supply. If isolation doesn’t stop the issue or the situation demands it, the APU bleed can be shut down and fire procedures activated, which may involve halting the APU and initiating fire Detection and suppression actions per procedures. Relying on visual inspection or smell alone isn’t sufficient because leaks can be hidden in ducts or plumbing and may not be detectable by sight or odor, yet they can significantly impact cabin pressurization, environmental control, and safety.