What condition can cause the E.P.R. indication to decrease falsely when the P sub T probe at the engine nose dome is iced closed?

When the P sub T probe at the engine nose dome becomes iced closed, it can lead to a false indication of the Engine Pressure Ratio (E.P.R.). Under these circumstances, anti-ice systems are often employed to functionally prevent ice formation on critical components. However, if these systems introduce pressurized air into the nose dome, it can lead to erroneous pressure readings.

In this case, the anti-ice air may not allow the normal airflow through the pressure probe, causing the E.P.R. to read lower than it actually is because the sensed pressure does not accurately reflect the operational conditions of the engine. This results in the E.P.R. indicator showing a reduced value, thereby indicating a false decrease in engine performance.

Understanding how anti-ice air interacts with the pressure measurement system helps to clarify the reasoning behind identifying this condition as a source of false E.P.R. readings. It's crucial for flight engineers to recognize the operational implications of ice formation and the corrective actions taken to maintain accurate engine performance readings during flight.