Cold soaked means the airplane has been exposed to temperatures of what and for how long?

• A. -30C or below for more than 8 hours
• B. -25C for more than 4 hours
• C. -40C for at least 2 hours
• D. -20C for 6 hours

Answer: (A)

Cold soak is about how cold and for how long the aircraft is left in the outside air long enough for its systems and fluids to reach the ambient temperature. The standard definition here is exposure to minus 30 degrees Celsius or colder for more than eight hours. This combination ensures the fuel, lubricants, and other onboard fluids, as well as the airframe, reach a true cold-soak condition so any ice formation or moisture behavior can be observed under realistic extreme-cold storage scenarios.

Why that threshold is the best fit: -30 C or colder is well into the subfreezing range where moisture in fuels or condensates can become problematic, and eight hours provides enough time for thermal equilibrium throughout the aircraft’s tanks and lines, not just surface areas. The lengthy duration matters because shorter exposures may not allow all components to reach the same cold temperature, which would miss the true behavior seen in everyday cold-soak scenarios.

The other options don’t align with the standard cold soak criteria because they either don’t reach as cold a temperature or don’t last long enough to ensure full equilibration of the aircraft’s systems.