(a)  
When no FCC is in command or when more than one FCC is in command, the setting of the captain's AIR DATA SOURCE SELECT switch determines which input is used. If the switch is set to L or C, the input at port A is used (left or center ADC output). If the switch is set to R, the input at port B is used (right or center ADC output depending on the position of the first officer's AIR DATA SOURCE SELECT switch).

 (b)  
When only one FCC is in command, that FCC alone controls the selection of the input. If the left or center FCC is in command, the input at port A is used (left or center ADC output). If the right FCC is in command, the input at port B is used (right or center ADC output).

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 (3)  
The baro-corrected altitude is compared to the selected altitude and this difference is compared to the altitude approach and capture points to determine mode of operation. In approach mode, the crew alerting card outputs an altitude advise discrete. In capture mode, the altitude advisory is disabled and the deviation logic is enabled. In deviation mode, the crew alerting card outputs an altitude alert discrete which remains active until the selected altitude is recaptured or the altitude alert system is reset or inhibited.

 (4)  
The crew alerting card outputs an altitude alert inop discrete to the SCID #1 card for transmission to the EIU's if a fault is detected in the altitude alert system or if any system inputs being used are missing.

 C. Functional Description - Altitude Alert Indications Envelope (Fig. 3)
 (1)  
The crew alerting card provides discrete outputs to the EIU's and aural synthesizer cards to generate altitude alert system indications. Altitude advisory indications are generated when in approach mode; altitude alert indications are generated when in deviation mode. Indications are removed when in capture, reset, or inhibit mode.

 (2)  
The following indications are generated when in approach mode:

 (a)  
The altitude readout box on the PFD's changes from single-stroked, half-intensity white to triple-stroked, full-intensity white.

 (b)  
A white box is displayed around the selected altitude readout on the PFD's.

 (c)  
The C chord advisory aural sounds as the airplane crosses the altitude approach point (900 feet).

 (3)
The following indications are generated when in deviation mode:

 (a)  
The altitude readout box on the PFD's changes from single-stroked, half-intensity white to double-stroked, full-intensity yellow.

 (b)  
The caution message >ALTITUDE ALERT is displayed on the main EICAS display.

 (c)  
The master caution light comes on.

 (d)  
The level B owl caution aural sounds as the airplane crosses the altitude capture point (300 feet).

 D. Control
 (1)  Turn on procedure
 (a)  
Ensure that the crew alerting card is installed in the MAWEA and that neither front panel LED is lit.

 (b)  
Ensure that all interfacing systems are operational.

 (c)  
Set a selected altitude on the MCP.

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CHORD AURAL  1 
+900' 
ALTITUDE  LEVEL B AURAL 
　
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