*
EPR reference/target

*
Actual EPR

*
EPR command.

EPR maximum is the maximum thrust limit. The EEC and the thrust management function of the AIMS calculate EPR maximum. The maximum available EPR is always set in the full forward thrust lever position.
EPR reference/target is the best value for the thrust mode that is set. The thrust management or flight management function of AIMS supplies EPR reference/target.
Actual EPR is the ratio of turbine exhaust pressure (P4.95) to engine inlet pressure (P2). The EEC calculates the EPR.
EPR command is set by thrust lever position. The thrust lever angle resolver sends lever position to the EEC. A command sector shows the difference between the engine actual EPR and EPR command.
Alternate Mode (N1) -Automatic
Some faults make the EEC switch to the alternate (N1) mode automatically. This is also called a soft reversion. In this alternate mode, the EICAS display does not show EPR indications. The EICAS display shows the normal N1 indications.
Alternate Mode (N1) -Manual
You manually select the alternate mode when you move the mode switch to ALTN (switch out). This is called a hard reversion. In this alternate mode, the EICAS display does not show EPR indications. These N1 indications show:
*
N1 maximum

*
N1 reference/target

*
Actual N1

*
N1 command.

N1 maximum is the maximum thrust limit. The thrust management function of the AIMS calculates N1 maximum. If the thrust lever is set to the full forward position in the alternate mode, N1 rotor speed can exceed N1 maximum.
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ENGINE INDICATING -EPR -FUNCTIONAL DESCRIPTION

N1 reference/target is the best LPC rotor speed for the thrust mode that is set. The thrust management or flight management function of the AIMS supplies N1 reference/target.
Actual N1 is the LPC rotor speed.
N1 command is set by thrust lever position. The EEC calculates N1 command. A command sector shows the difference between N1 command and actual N1.
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ENGINE INDICATING -EPR -FUNCTIONAL DESCRIPTION

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PW4000 SERIES ENGINES

777 AIRCRAFT MAINTENANCE MANUAL

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ENGINE INDICATING -ENGINE TACHOMETER -GENERAL DESCRIPTION

Purpose
The engine tachometer system supplies the N1 and the N2 speed signals to the EEC. The EEC sends the N1 and N2 signals to engine and airplane systems.
General Description
The N1 speed transducer supplies the analog N1 signal to the EEC. The permanent magnet alternator (PMA) frequency supplies the analog N2 signal to the EEC. See the engine control section for more information about the dedicated alternator (SECTION 73-21).
　
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