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A / PW4000 SERIES /
747-400 / ENGINES /FAULT ISOLATION/MAINT MANUAL ////////////////////////
SEE J
INLET COWL RIGHT FAN COWL PANEL(REF)
414 (ENGINE 1)
424 (ENGINE 2) ENGINE 434 (ENGINE 3) FLANGE A 444 (ENGINE 4) (REF)
ENGINE ACCELEROMETER T677
FAN CASE
(REF)

FWD
J
Engine Indicating - Component Location
Figure 102 (Sheet 4)

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A / PW4000 SERIES /
747-400 / ENGINES /FAULT ISOLATION/MAINT MANUAL ////////////////////////

AVM SIGNAL CONDITIONER, M118, M7846

Engine Indicating - Component Location
Figure 102 (Sheet 5)

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M03854
ENGINE PRESSURE RATIO INDICATING SYSTEM - DESCRIPTION AND OPERATION
___________________________________________________________________
 1.  General
_______
 A.  The indicating system for the engine pressure ratio includes the EEC inlet probe for the total pressure/temperature (PT2/TT2), two probes for the engine pressure ratio (PT4.95), and the manifold for the engine pressure ratio (PT4.95).
 B.  The indication of the engine pressure ratio (EPR) is shown on the main EICAS display.
 2.  EEC Inlet Probe for the Total Pressure/Temperature (PT2/TT2) (Fig. 1)
____________________________________________________________
 A.  The PT2/TT2 probe is installed in the inlet cowl at the 1 o'clock position. This probe senses temperature and pressure at the engine inlet and transmits signals to the EEC to give a baseline for comparison with the exhaust signals. For more information on the PT2/TT2 probe, refer to Fuel Control System, AMM 73-21-00/001.
 3.  Probe for the Engine Pressure Ratio (PT4.95) (Fig. 1)
____________________________________________
 A.  There are two EPR (PT4.95) probes, which extend radially into the exhaust stream to sense the engine exhaust gas pressure, installed in the turbine exhaust case at the 4 and 10 o'clock positions.
 B.  These probes also serve as housings of the probes for the exhaust gas temperature (EGT) and are connected to each other and the EEC by the EPR manifold.
 4.  Manifold for the Engine Pressure Ratio (PT4.95) (Fig. 1)
_______________________________________________
 A.  The EPR (PT4.95) manifold connects the two EPR probes to the EEC manifold with a tee fitting at the 7 o'clock position on the turbine exhaust case, and then gives an averaged pneumatic pressure signal to the EEC.
 5.  Indication for the Engine Pressure Ratio (Fig. 2)
________________________________________
 A.  EPR is displayed as a ratio of exhaust gas pressure to inlet total pressure on the main EICAS display on a verticle bar graph for each engine and also in digital (boxed, just above graph). For more information on EPR indication, refer to Integrated Display System, AMM 31-61-00/001.
 6.  Operation (Fig. 3)
_________
 A.  Functional Description
 (1)  
The EPR indicating system is operational when 28 volts dc is applied to the EEC (or when N2 rpm is more than 10%).

 (2)  
The engine inlet pressure is sensed by the PT2/TT2 probe and is sent to the EEC. The engine exhaust gas pressure is sensed by two EPR (PT4.95) probes, averaged in the EPR (PT4.95) manifold, and is sent to the EEC. Transducers internal to the EEC convert the PT2 and PT4.95 inputs into an EPR signal.
　
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