What is the minimum ambient temperature for starting a cold-soaked APU on the ground?

What is the minimum ambient temperature for starting a cold-soaked APU on the ground?

• A. -40C
• B. -20C
• C. 0C
• D. -60C

Answer: (A)

When an APU sits in very cold weather, its lubricants and fuels thicken and the starter and battery have less cranking power, so the aircraft defines a minimum ambient temperature for a safe, reliable ground start. The established floor for starting a cold-soaked APU is -40 C, meaning you can start if the ambient is at or above this temperature but not reliably below it without preheating. Warmer conditions, like -20 C or 0 C, are within the allowed range and fine to start, while -60 C would be outside the allowable envelope.

When an APU sits in very cold weather, its lubricants and fuels thicken and the starter and battery have less cranking power, so the aircraft defines a minimum ambient temperature for a safe, reliable ground start. The established floor for starting a cold-soaked APU is -40 C, meaning you can start if the ambient is at or above this temperature but not reliably below it without preheating. Warmer conditions, like -20 C or 0 C, are within the allowed range and fine to start, while -60 C would be outside the allowable envelope.