DIRECTOR INDICATORSWITCH PANEL
ARINC CENTER AND RIGHT CMDENGLEFT AND RIGHT F/D ON LEFT,
429
DATA
AFDS DIGITAL OUTPUTS
ARINC FOR ADI DISPLAYS
429
AFDS Data Switching
Figure 5 (Sheet 2)
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MAINTENANCE MANUAL
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(b) AIRPLANES WITHOUT CONTROL WHEEL STEERING; positioning the captain's or first officer's F/D switch to ON permits the FCCs to compute F/D commands and activates the EADI FMA. These commands can be generated simultaneously by an FCC engaged in CMD mode.
(3)
F/D Switching
(a)
The FLT DIR switch on the left (right) INSTR SOURCE SEL panel is a three-position, rotary switch which provides a ground to the left, center or right FCC. This enables that FCC to supply computed F/D signals to all SGs.
(b)
The left LFT DIR switch supplies a ground to the left and center EFIS SGs when in the L or R position. These ground are identified as L F/D SEL 1 and L F/D SEL 2 respectively.
(c)
The right FLT DIR switch supplies a ground to the right and center EFIS SGs when in the R or L position. These grounds are identified as R F/D SEL 2 and R F/D SEL 1 respectively.
(d)
The FLT DIR switch ground logic allows the EFIS SGs to determine which F/D data input to use for the L or R F/D display (EADI). When a FLT DIR switch is in the C position, no F/D source ground is supplied.
(4)
EFI Switching
(a)
The EFI switches on the left and right INSTR SOURCE SEL panels are alternate action pushbutton switches. The legend ALTN (alternate) is displayed when the associated switch is pressed to select another Symbol Generator (SG). The EFI switches control the DISPLAY DRIVE SELECT inputs to the left and right EFIS SGs and the EFI select to the center EFIS SG. Each switch in the normal position supplies an open to the DISPLAY DRIVE SELECT input. This enables the left or right SG to select the source of video for data processing. If either EFI switch is in the ALTN position, the normal SG for that switch is disabled.
(b)
The POWER DOWN input to the left SG is an open when the left switch is normal, but grounded when in ALTN. This ground disables the left SG. The POWER DOWN input to the center SG is grounded when the two EFI switches are normal. Thus, the center SG is disabled. If either EFI switch is in ALTN, the center SG is powered up. The right SG has a permanently open POWER DOWN input.
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(c) The EFI SELECT input controls which data source is used by the center SG. This signal is routed through both EFI source select switches. When open, the center SG selects the left data source. This signal input is an open under all combinations of EFI switch positions except when the left switch is in normal and the right is in ALTN. If both switches are set at ALTN, the left has priority use of the center SG. The EICAS displays a yellow INSTR SW message, the master CAUTION light illuminates, and a single tone chime sounds.
(5) FCC Program Pin Connections (Fig. 6)
(a)
The FCC program pins allow selection of different control laws and operational characteristics by either connecting an option pin to ground or leaving the pin not connected at the FCC shelf connector. The following description of the FCC program options covers the actual airplane configuration:
(b)
FCC configuration - provides five pin connections at the shelf to identify the aircraft type. The FCC reads these pins as a binary code; there are 32 possible combinations. Pin 1 is grounded for all 757-200 airplanes.
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