What happens to engine pressure ratio (EPR) when thrust levers are advanced?

The concept of engine pressure ratio (EPR) is crucial in understanding how jet engines function, particularly during different phases of flight. When thrust levers are advanced, the EPR initially increases. This is because as the thrust levers are pushed forward, fuel flow into the engine increases, and the engine subsequently produces more thrust.

The initial decrease in EPR mentioned in the choice indicates a misunderstanding of engine dynamics. What actually occurs is that advancing the thrust levers leads to an increase in the pressure ratio across the engine. This means that the difference in pressure between the compressor and turbine stages becomes greater, which contributes to higher thrust output.

Furthermore, EPR is not solely determined by altitude; while it can be affected by various factors, it is primarily driven by engine parameters including fuel flow and airflow. Thus, thrust lever positioning is a critical aspect that significantly affects the EPR.

In summary, the correct choice reflects the immediate increase in EPR as the thrust levers are advanced, which is a fundamental part of engine performance management in aviation. This understanding is essential for effectively managing engine operation and optimizing thrust during critical flight phases such as takeoff and climb.