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C. Stabilizer Trim Limit Switches (Ref 27-41-00)
(1) The purpose of the stabilizer trim limit switches is to limit amount of stabilizer travel that can be commanded by outputs from the FCC. The stabilizer trim limit switches are located in the stabilizer access area just aft of the stabilizer jack screw. There are six stabilizer trim limit switches which are all mechanically operated by a cam assembly and movement of the stabilizer. Electrical connections are provided to each to indicate when the switches are in the open or closed position.
17. DFCS Power Distribution (Fig. 4, 5, 6)
_______________________
A. DFCS power is derived from two ac and three dc power buses. The buses involved are:
-
number 1 and 2, 115 volt ac electronic buses
-
number 1 and 2, 28 volt dc electronic buses
-28 volt dc switched hot battery bus.
B. When either FCC A or FCC B issues G/S engaged signal, the signal is sent to the AFC accessory unit or IFSAU. The logic is used to remove the ground from TR-3 disconnect relay. With the ground removed, the relay opens which will provide isolated power supplies during either F/D approach or A/P approach. During dual channel operation, it is required that each FCC be on an isolated power source. Normal condition is FCC A on generator bus 1 and FCC B on generator bus 2. The normal side coils of the transfer relays are monitored by the FCCs to insure isolated power sources. If one of the generator buses fails, the transfer relay is switched to the other generator bus by the generator control unit (GCU), removing the normal coil voltage and applying alternate coil voltage. Loss of the power transfer discrete due to the loss of the normal coil voltage to the FCC inhibits dual channel operation. An ac power transfer disengages both autopilot channels. The second channel is locked out if two isolated power sources are not available. In order to re-enable dual channel functions, the two transfer buses must be powered from isolated sources. This can be accomplished by returning the failed generator to service or by putting the APU on line.
C. 115 Volt AC Electronic Bus 1 provides power to:
(1)
C849 STABILIZER TRIM (P18-0), 3-phase, 115 volts ac to the stabilizer trim servo.
(2)
C1041 SNSR EXC A (P18-1), 115 volts ac to the AFC ACC unit or IFSAU. An autotransformer in the AFC ACC unit (or IFSAU) provides 26 volts ac to A FCC and some of the sensors for the A channel.
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STABILIZERTRIM SERVO
AFC ACC
UNIT OR
INTEG FLT
SYS ACC UNIT
A FCC
MCP
A FCC
ENGAGEINTERLOCK
A FCC
CAPT FMS WARN,MCP & A FCC P18-1 LOAD CONTROL
1 BATTERY BUS LOGIC INCLUDESP6-2 LOAD CONTROLCENTER - LEFT RELAYS R326, R1 AND R355 CENTER - RIGHT
DFCS Power System Interface SchematicFigure 4
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