What does an engine pressure ratio (EPR) indicator measure?

What does an engine pressure ratio (EPR) indicator measure?

• A. Engine pressure ratio (EPR) indicates thrust developed by a turbofan engine and is instrumented by total pressure pickups in the engine inlet and turbine exhaust
• B. It measures engine RPM
• C. It measures fuel flow
• D. It measures ambient air temperature

Answer: (A)

The engine pressure ratio indicator measures how the engine’s total pressure changes from inlet to exhaust, which correlates with the thrust the engine is producing. It uses two pressure readings: one from the engine inlet (total pressure entering the core) and one from the exhaust side (total pressure after the compressor/turbine path). The ratio of exhaust pressure to inlet pressure rises as the engine delivers more thrust, so a higher EPR value indicates more thrust on a turbofan. This instrument is not measuring engine RPM, fuel flow, or ambient air temperature—those are tracked by other gauges.

The engine pressure ratio indicator measures how the engine’s total pressure changes from inlet to exhaust, which correlates with the thrust the engine is producing. It uses two pressure readings: one from the engine inlet (total pressure entering the core) and one from the exhaust side (total pressure after the compressor/turbine path). The ratio of exhaust pressure to inlet pressure rises as the engine delivers more thrust, so a higher EPR value indicates more thrust on a turbofan. This instrument is not measuring engine RPM, fuel flow, or ambient air temperature—those are tracked by other gauges.