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747-400 MAINTENANCE MANUAL
 F. Terrain Display Select Switch
 (1)  The TERR Terrain Display Select Switches are located on the captain's and first officer's EFIS control panels in the pilot's glare shield. Each switch provides a momentary ground discrete to the EGPWC. Pressing the TERR switch causes terrain data to be displayed if the navigation display (ND) is in a displayable mode such as MAP, CTR MAP, Expanded VOR, or APP. If the ND is not in a displayable mode, then pressing the switch arms the terrain display which allows terrain to be displayed immediately when a displayable ND mode is selected.
 G. Navigation Display - Terrain Awareness Information
 (1)  
Terrain awareness information is displayed on each navigation display (ND) when selected on the captain's or first officer's EFIS control panel. It can also be displayed automatically if a terrain caution or warning alert occurs and if it has not been selected by the pilot or first officer. The NDs are located in the main panels.

 (2)  
The NDs can display the following Terrain Awareness Alerting and Display (TAAD) messages:

 Red TERRAIN - Active TAAD warning alert
 Amber TERRAIN - Active TAAD caution alert
 Amber TERR FAIL - Terrain Clearance Floor (TCF), TAAD failed
 Amber TERR POS - Horizontal position data is not accurate or is not available
 Amber TERR OVRD - Terrain override switch is in the OVRD position
 Cyan TERR TEST - EGPWS system is in self test mode
 Cyan TERR - Terrain data is being displayed
 Amber TERR RANGE DISAGREE - The selected EFIS control panel range and the range of the terrain do not agree
 Amber MAP/TERR RANGE DISAGREE - The selected EFIS control panel range and the range of the terrain and MAP display do not agree
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747-400 MAINTENANCE MANUAL
 H. Weather Radar/Terrain Display Select Relays
 (1)  The Weather Radar/Terrain Display Select Relays are driven directly by an analog ground discrete output from the EGPWC. The display system receives Weather Radar data and EGPWS terrain data on ARINC 453 type busses. The relays are used to switch the source of the ARINC 453 data between the EGPWS and the Weather Radar. The default (de-energized) position of the relays is the Weather Radar display position.
 I. Warning Speakers
 (1)  The aural warning speakers are located on each side adjacent to the pilots' overhead panel P5. The speakers come on to annunciate the GPWS warning and advisory aural messages. The MAWEA controls the speakers.
 J. EICAS Display Units
 (1)  The EICAS display units are located on the center instrument panel. They display the GPWS failure message if there is a GPWS system fault (Ref 31-41-00).
 3.  Operation_________
 A. Functional Description
 (1)  
Mode 1 Function (Fig. 2)

 (a)  Mode 1 provides warnings and advisories when the airplane has a large descent rate with respect to the altitude above ground level (AGL) during descent and approach. If the airplane barometric descent rate becomes excessive, the aural SINKRATE message is heard and the amber GND PROX light comes on. If the descent rate becomes severe, the aural changes to PULL UP, and the red PULL UP indication shows and the master warning lights come on.

 (2)  
Mode 2 Function (Fig. 2)

 (a)  Mode 2 provides warning and advisories for excessive closure rates to the terrain with respect to altitude AGL, phase of flight, and speed. Mode 2 has two sub-modes, Mode 2A and 2B. 1) Mode 2A advisories and warnings are given when the airplane
 is not in landing configuration. If the terrain closure rate is excessive, the aural TERRAIN TERRAIN message is heard and the amber GND PROX light comes on. If the condition is not corrected, the aural message changes to the PULL UP warning, and the red PULL UP indication shows and the master warning lights come on.
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