Takeoff with engine fuel temperature indications below what value is prohibited?

• A. 5C
• B. -5C
• C. 0C
• D. -10C

Answer: (A)

Takeoff with fuel at higher reliability requires keeping the fuel system out of the ice-forming range for any entrained water. In aviation fuel, even when the fuel itself can remain liquid well below freezing, water contained in the fuel can begin to freeze as temperatures approach 0°C. Ice crystals can clog fuel lines or filters just as the engines demand maximum fuel flow during takeoff, risking a loss of power when you need full performance. Setting a minimum fuel temperature of 5°C creates a safety margin above the point where ice formation from water might occur, helping ensure smooth engine operation and reducing the chance of fuel system blockages. That’s why taking off is prohibited if engine fuel temperature indications are below 5°C. The other options would allow takeoffs at temperatures where ice formation in the fuel system could become a real hazard, which is not permitted.