What can high cylinder head temperature during flight indicate?

High cylinder head temperature during flight is a crucial indicator of engine performance and can reflect the mixture setting being used. When an aircraft is operating at high power with the mixture set too lean, it means that there is insufficient fuel in relation to the amount of air entering the engine. This can lead to incomplete combustion, which generates excess heat in the engine and results in elevated cylinder head temperatures.

In this scenario, the engine is working harder due to the high power setting, but because the fuel mixture is too lean, there isn't enough fuel to absorb and dissipate the heat generated. This imbalance can cause significant stress on the engine components and can lead to potential damage if not addressed. Monitoring and adjusting the fuel mixture accordingly is vital to maintaining optimal engine performance and ensuring safe operation.

The other options, while related to engine performance and operation conditions, do not directly link high cylinder head temperatures with an inadequate fuel mixture like a lean setting does. Low power with a rich mixture generally cools the engine, while high altitude flying doesn't inherently cause high temperatures either, and incorrect propeller pitch primarily impacts the aircraft's thrust and efficiency rather than directly affecting cylinder head temperatures.