How do ambient temperature and altitude affect fuel metering and engine performance?

• A. Lower air density at higher altitude or higher temperature reduces mass flow; fuel control may increase fuel to maintain power, which can affect EGT
• B. Higher air density reduces fuel needs
• C. The engine performance is unaffected by altitude or temperature
• D. Fuel metering is completely independent of ambient conditions

Answer: (A)

Ambient temperature and altitude change air density, which directly affects how much air mass enters the engine for a given speed and intake conditions. Fuel metering is generally scheduled to match the air mass flow to maintain an appropriate fuel/air ratio. When density is lower (higher altitude or hotter air), the same engine speed delivers less air mass. To try to keep power or a target turbine inlet condition, the fuel control may inject more fuel to compensate for the reduced air, but there’s still less air to burn, so the mixture becomes richer and the combustion temperature rises. That higher heat load shows up as a higher exhaust gas temperature and can push engine limits if not managed.