Which statement describes the function of the APU during hot shutdown protection?

Which statement describes the function of the APU during hot shutdown protection?

• A. The automatic time-delay feature closes the bleed air valve to reduce load and temperature before shutdown.
• B. The bleed air valve remains wide open to cool quickly.
• C. The fuel valve opens to increase cooling.
• D. Ignition is activated to aid cooling.

Answer: (A)

Hot shutdown protection aims to protect the APU by allowing a controlled cooldown as it winds down. The automatic time-delay feature closes the bleed air valve so the APU stops supplying bleed air to the aircraft systems while it’s still running down. By cutting bleed air, the turbine and compressor aren’t working as hard, which reduces mechanical load and the heat being produced, helping the APU cool down more safely and avoid thermal stress. Opening the bleed valve or adding fuel or ignition would keep or increase the heat and load, making shutdown more aggressive and riskier.

Hot shutdown protection aims to protect the APU by allowing a controlled cooldown as it winds down. The automatic time-delay feature closes the bleed air valve so the APU stops supplying bleed air to the aircraft systems while it’s still running down. By cutting bleed air, the turbine and compressor aren’t working as hard, which reduces mechanical load and the heat being produced, helping the APU cool down more safely and avoid thermal stress. Opening the bleed valve or adding fuel or ignition would keep or increase the heat and load, making shutdown more aggressive and riskier.