Definition
In a turbojet or turbofan engine, the ratio of turbine discharge (exhaust) total pressure to compressor inlet total pressure. EPR is used as a primary indication of thrust output on many jet engines and is displayed on a dedicated cockpit gauge.
Plain English
EPR is a number that compares the air pressure leaving the engine to the air pressure entering it. The bigger the difference, the more thrust the engine is producing.
Context Anchor
Seen on turbine-engine cockpit instruments, power-setting charts, and procedures that tell the pilot what engine power to set.
Derivation
The name describes exactly what is measured: a ratio of two engine pressures — the pressure at the back compared to the pressure at the front. A higher ratio means the engine is doing more work on the air passing through it, which translates to more thrust.
Why Pilots Care
Enables precise thrust setting and monitoring to ensure safe takeoff, climb, cruise, descent, and landing performance.
Intuition Check
EPR does not mean the actual thrust force itself. It is a pressure comparison used to indicate how much thrust the engine is producing.
Example Sentence 1
After lining up on the runway, the captain advanced the thrust levers and called for takeoff EPR.
Example Sentence 2
During cruise the crew adjusted power to hold a steady EPR reading for fuel-efficient flight.