Minimum in-flight fuel temperature is ____°C above the freezing point of fuel or ___°C, whichever is higher.

• A. 5/-40
• B. 3/-43
• C. 1/-42
• D. 4/-44

Answer: (B)

The situation checks how the minimum in-flight fuel temperature is determined: you must stay above both a margin above the fuel’s freezing point and a fixed negative limit, taking whichever value is higher.

Fuel freezing point is a property of the fuel type, and a 3°C margin is added to that point to ensure the fuel remains flowable and doesn’t gel. There’s also a hard lower limit of -43°C. Whichever of these two values is higher becomes the controlling minimum.

In practice, with typical jet fuel freezing points around -46 to -50°C, the margin above freezing point (FP + 3) is about -43°C or lower. The fixed -43°C limit is then the higher value, so the minimum in-flight fuel temperature is -43°C. This is why the correct formulation is 3°C above the freezing point or -43°C, whichever is higher.