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747-400 MAINTENANCE MANUAL
 2)  Mode 2B advisories and warnings are given when the flaps are in landing configuration or during an ILS approach with glideslope deviation less than plus or minus 2 dots. If the terrain closure rate is excessive, the aural TERRAIN message is heard repeatedly and the amber GND PROX light comes on. If the condition is not corrected after 1.6 seconds, the aural message changes to the PULL UP warning (repeated continuously), and the red PULL UP indication shows and the master warning lights come on. If the terrain closure rate is excessive, with the landing gear extended and the flaps in the landing configuration, the PULL UP aural warning is replaced by the TERRAIN aural caution.
 (3)  
Mode 3 Function (Fig. 2)

 (a)  The mode 3 advisory signals are provided when an excessive altitude loss occurs during takeoff or missed approach. This function occurs for either the gear or flaps up. If barometric altitude decreases excessively during the initial takeoff climb or during a go-around, the DON'T SINK aural caution sounds repeatedly, and the amber GND PROX light comes on. The caution continues until a positive rate of climb is established. If the airplane descends again before climbing to the original descent altitude, another caution sounds based on the original descent altitude.

 (4)  
Mode 4 Function (Fig. 2)

 (a)  Mode 4 advisory signals are provided for insufficient terrain clearances with and without the landing gear up. Mode 4 has three sub-modes: Mode 4A, 4B, and 4C. 1) Mode 4A generates advisory signals for unsafe terrain
 clearances with the landing gear up and flaps not in landing configuration. When the airspeed is less than 190 konts, the TOO LOW GEAR aural caution is repeated, and the amber GND PROX light comes on. If the airspeed is more than 190 knots, the TOO LOW TERRAIN aural caution is repeated, and the GND PROX light comes on.
 2)  Mode 4B provides a caution alert when the landing gear is down and the flaps are not in the landing position. If the airspeed is less than 159 knots, the TOO LOW FLAP aural caution is repeated and the amber GND PROX light comes on. If the airspeed is more than 159 knots, the TOO LOW TERRAIN aural caution is repeated and the amber GND PROX light comes on. If the gear is not down, the aural TOO LOW GEAR message replaces the TOO LOW FLAP caution message. a) The TOO LOW GEAR caution is inhibited when the GND PROX
 GEAR OVRD switch is pressed.
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747-400 MAINTENANCE MANUAL
"SINKRATE"
"PULL UP!"
EXCESSIVE DESCENT RATE MODE 1 
TERRAIN" "TERRAIN  "PULL UP!" 
TERRAIN" "TERRAIN  "PULL UP!" 

MODE 2A  MODE 2B 
EXCESSIVE TERRAIN CLOSURE RATE  EXCESSIVE TERRAIN CLOSURE RATE 
(FLAPS AND GEAR DOWN) 
"DON'T SINK" 

MODE 3
ALTITUDE LOSS AFTER TAKEOFF OR GO-AROUND

Ground Proximity Warning System Modes
Figure 2 (Sheet 1)

K61007
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747-400
MAINTENANCE MANUAL

"TOO LOW 
TERRAIN" 
AIRCRAFT SLOWED TO 
LESS THAN 190 KTS 

TERRAIN" "TOO LOW  "TOO LOW GEAR" 
(GEAR UP) MODE 4A UNSAFE TERRAIN CLEARANCE  RUNWAY 
"TOO LOW TERRAIN"  LESS THAN 159 KTS GEAR DOWN AIRCRAFT SLOWED TO 

TERRAIN" "TOO LOW  FLAPS" "TOO LOW 
RUNWAY 
MODE 4B (GEAR DOWN) UNSAFE TERRAIN CLEARANCE 
"TOO LOW TERRAIN" 

"TOO LOW TERRAIN"
MODE 4C
UNSAFE TERRAIN CLEARANCE
(TAKEOFF OR GO-AROUND)

Ground Proximity Warning System Modes
　
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