(5)
Microswitch Pack Assembly (Fig. 3)
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A
757
MAINTENANCE MANUAL
LOAD SHED/PRESSURE CONTROL SWITCH, S17
SPEED BRAKE RETRACT
TMS LEFT THRUST LEFT SWITCH, S10
REVERSE SWITCH, S12
SPACER
LANDING WARNING LEFT SWITCH, S1
SPACER LEFT AUTOBRAKE/AUTOBRAKE RTO SWITCH, S2
EEC 0FF SWITCH, S19 LEFT AUTOBRAKE/AUTOBRAKE RTO SWITCH, S3
LOAD SHED/PRESSURE TMS RIGHT THRUST
CONTROL SWITCH, S18 REVERSE SWITCH, S16
SPEED BRAKE RETRACT SPACER
RIGHT SWITCH, S14 LANDING WARNING RIGHT SWITCH, S5 SPACER RIGHT AUTOBRAKE/AUTOBRAKE EEC 0FF RTO SWITCH, S6 SWITCH, S20
RIGHT AUTOBRAKE/AUTOBRAKERTO SWITCH, S7
1
LEFT AUTOBRAKE/AUTOBRAKE
LANDING WARNING LEFT
RTO SWITCH, S2
SWITCH, S1 TMS LEFT THRUST
LEFT AUTOBRAKE/AUTOBRAKE
REVERSE SWITCH, S12
RTO SWITCH, S3
LEFT THRUST REVERSE INDICATION SWITCH, S23
LEFT THRUST REVERSE CONTROL SWITCH, S21
SPACER LOAD SHED/PRESSURE CONTROL LEFT SWITCH, S17 EEC OFF
SPEEDBREAK RETRACT
LEFT LEFT SWITCH, S10SWITCH, S19 TMS RIGHT THRUST REVERSE SWITCH, S16
LANDING WARNING
RIGHT THRUST REVERSE RIGHT SWITCH, S5
INDICATION SWITCH, S24
RIGHT THRUST REVERSE RTO SWITCH, S6 RIGHT AUTOBRAKE/AUTOBRAKE CONTROL SWITCH, S22
LOAD SHED/PRESSURE RIGHT AUTOBRAKE/AUTOBRAKE
CONTROL RIGHT SWITCH, S18 RTO SWITCH, S7
SPACER SPEEDBRAKE RETRACT
RIGHT SWITCH, S14 EEC OFF RIGHT SWITCH, S20
1
GUN 001-008, 010, 101-104 WITHOUT SB 78-32.
2 2
GUN 001-008, 010, 101-104 WITH SB 78-32
AND GUN 009, 011-099, 105-999.
Microswitch Pack Assembly
Figure 3
C98970
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(a)
The microswitch pack assembly is directly under the clutch pack assembly. It is held in place by four bolts. The assembly is capable of containing 16 sets of switches. The number of switches installed depends on airplane configuration. The switches contained in the assembly are shown in Fig. 3.
(b)
The thrust reverse switches are used by the TMS. One set is operated by the left thrust lever and the other set is operated by the right thrust lever. The switches are actuated when the reverse thrust levers are engaged. Thrust limit computation by the TMC is put in the reverse mode and the autothrottle is disengaged. The microswitch pack assembly includes wiring and electrical connectors that mate with airplane wiring.
(c)
The arm assembly on the flap handle is moved by the flap lever quadrant in the flaps 1 or greater position. The switch assembly contains four sets of switches which are activated by the arm assembly movement. Three sets are used by the flight control computers. One set is used by the TMC.
3. Operation_________
A. Functional Description
(1) Thrust Management System - Block Diagram (Fig. 4)
(a) Thrust Control
1) Control of thrust is provided by the thrust levers (manually) and the A/T servomotor generator (automatically). They supply a mechanical input to the fuel flow governor, which is on the engine. The autothrottle PLA transducers on the engines provide power lever angle feedback to the TMC to close the servo loop. The EPR transmitters provide actual EPR to the Electronic Engine Control (EEC) and EICAS computers. The EEC uses this information along with throttle lever angle, air data, and bleed status to: a) Control and limit thrust b) Linearize the throttle-to-thrust-rating relationship c) Drive the engine thrust indicator command sector on the
upper EICAS display unit.
(b) Flight Deck Indications
1) The primary engine format is shown on the upper EICAS display unit. Engine parameters shown on this format are those required to set and monitor engine thrust. Digital displays are provided for reference EPR, thrust limit mode, total air temperature, and selected temperature. The EPR indicators on the EICAS display unit provide an analog type round dial display for reference EPR, commanded EPR, and actual EPR. Caution advisory messages relating to the TMS are also displayed on the EICAS display unit.
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