What prevents the APU from exceeding its safe operating limits when the bleed air valve is fully open?

What prevents the APU from exceeding its safe operating limits when the bleed air valve is fully open?

• A. The bleed air valve automatically closes when overpressure occurs.
• B. The APU automatically shuts down if overheating.
• C. The FADEC monitors the load and regulates the fuel going to the APU to prevent it from exceeding its safe limits.
• D. The control lever locks in place.

Answer: (C)

When the bleed air valve is fully open, the APU would demand a high load. The protection comes from the FADEC, a full-authority digital control that continuously monitors the APU’s parameters (speed/load and temperature) and regulates fuel flow to keep RPM, load, and EGT within safe limits. If the bleed demand threatens an overlimit condition, the FADEC reduces fuel delivery to prevent exceeding those limits, even with the valve wide open.

When the bleed air valve is fully open, the APU would demand a high load. The protection comes from the FADEC, a full-authority digital control that continuously monitors the APU’s parameters (speed/load and temperature) and regulates fuel flow to keep RPM, load, and EGT within safe limits. If the bleed demand threatens an overlimit condition, the FADEC reduces fuel delivery to prevent exceeding those limits, even with the valve wide open.