(d)
Bleed Correction
1) If bleed air is being extracted, EPR limits are reduced. Discrete inputs select the amount of correction needed. No correction for cowl anti-ice is needed if the altitude is less than 8000 feet and the temperature is less than 7.8°C. If cowl anti-icing is operating under these conditions, the EPR correction is latched until an altitude of 14,000 feet or a speed of 0.45 Mach is obtained.
(e)
MAX EPR
1) The MAX EPR limit is calculated, stored, and sent to EICAS. The calculated value is displayed as two amber lines on the EPR indicators on the EICAS upper display unit.
(f)
REF EPR
1) The REF EPR limit is calculated and stored on the computer pass opposite of the MAX EPR pass. When the T/O mode is selected, the MAX select function chooses the highest value for REF EPR between REF calculated and MAX calculated minus
0.1. Thrust limit calculations are displayed on the EICAS display unit, and the EPR indicator "bug" is driven to the REF EPR. If the reverse mode is engaged, the REF EPR goes to No Computed Data (NCD) and the EICAS display is blank. During VNAV operation, the EPR indicator bug is driven to the FMC target EPR.
(11) Autothrottle - Takeoff Mode (Fig. 12)
(a) EPR TAKEOFF mode (T/O) is selectable on the TMSP only when the airplane is on the ground and the A/T ARM switch, located on the MCP, has been armed. Then, when the EPR (or THR) mode on the MCP is engaged on the ground, the thrust levers are driven until the (T/O) EPR REF is obtained.
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MAINTENANCE MANUAL
1
Autothrottle - Takeoff Mode
Figure 12
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M20700
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MAINTENANCE MANUAL
(b)
The T/O EPR REF, computed by the thrust limit function of the TMC, may be derated by assumed-temperature derating. The assumed temperature is inserted into the TMC either from the TMSP or from the FMC when VNAV is engaged. Assumed temperature derating of a takeoff thrust limit is achieved by inserting a temperature that is higher than both ambient and flat rated temperature.
(c)
Following engagement in EPR (or THR) T/O mode and reaching 80 kts CAS, the A/T servo is deactivated and THR HOLD is displayed on the EADI. THR HOLD prevents the thrust levers from retarding after T/O EPR REF has been obtained.
(d)
Annunciation of the EPR T/O mode engagement includes:
1) EPR (or THR) switch on MCP is illuminated.
2) EPR is displayed on EADI.
(12)
Autothrottle - EPR Mode (Fig. 13)
(a) The A/T can engage in an EPR (or THR) mode of CLB, CON, or CRZ during flight. Manual selection of CLB, CON, or CRZ EPR thrust limit is made by pressing the respective switch on the TMSP. Manual selection is displayed on EICAS. If the A/T is engaged in SPD or FLCH, the EPR (or THR) mode must be engaged through the MCP following selection of the EPR thrust limit on the TMSP.
(13)
Autothrottle - VNAV Mode (Fig. 14)
(a)
The VNAV mode engages when the VNAV switch is pressed and the FCC accepts the VNAV request. The MCP VNAV switch/light dot-bar matrix then illuminates.
(b)
Engaging the VNAV mode transfers control of pitch and thrust to the FMC. The TMC receives the VNAV mode engage status from the FCC. When VNAV is engaged, The TMC accepts mode requests along with target commands (EPR, Mach, or airspeed) from the FMC. The FMC request modes are EPR (or THR), SPD, Mach, idle, or dormant. The EPR (or THR) and SPD switch/lights do not illuminate during VNAV, and the IAS/Mach display on the MCP is blank. The EICAS display unit displays the TMC computed EPR REF and MAX EPR. The EPR indicator bug on the EICAS display is driven by the TMC to the FMC target EPR. During VNAV operation, the thrust levers are automatically driven to the FMC generated target EPR. The active autothrottle mode status is displayed on the lower left corner of the EADI.
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