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747-400 MAINTENANCE MANUAL
WEATHER
WEATHER DISPLAY
DISPLAY

SHOWN REVERSED FOR 
ILLUSTRATION PURPOSES 
Weather Radar Mode Displays 
Figure 5 

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IN AIR ALERT REGION

Predictive Windshear Alert Region

Figure 6

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L09478
 (c)
(d)

(e)

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747-400 MAINTENANCE MANUAL
 2) The PWS is automatically deactivated according to the following conditions and as shown on Fig. 7. a) The airplane is on the ground with the engines not at takeoff thrust and the WXR switch on the EFIS control panel is no set to the on position. b) The thrust reversers are applied on the ground. c) The airplane is in the air above 2300 AGL (climb).
Approach Mode of Operation
 1)  The PWS is automatically activated according to the following conditions and as shown on Figure 7.
 2)  The airplane is between 50 and 2300 feet.
 3) The PWS is automatically deactivated according to the following conditions and as shown on Figure 7. a) The airplane is on the ground with the engines below takeoff thrust. b) The thrust reverseres are not applied. c) The airplane is in the air above 2300 feet (go around).
Maintenance Operations
 1)  The weather radar system is manually deactivated for airplane engine run tests to prevent inadveretent radar activation due to the PWS automatic activation features. The PWS weather radar system is deactivated by opening the following WXR system circuit breakers. a) 115V AC WXR L R/T b) 115 V AC WXR R R/T
Antenna Scan During WXR and Windshear Operations (Figure 8).
 1)  The system must detect a windshear event, or microburst for two consecutive PWS sweeps in order to begin the alert annunciations. At the end of the second PWS sweep the alert condition is set and the proper alerts are annunciated.
 2)  The antenna tilt angle is set automatically during the PWS sweep independent of the tilt angle selected on the WXR control panel. This angle starts at 3.5 degrees down and is then adjusted based on the altitude inputs from the radio altimeters.
 3)  The antenna scan pattern as shown in Figure 8 is the same for takeoff and approach mode of operation. The system operation changes whenever the PWS is active. The WXR and PWS scans are reduced to | 45 degrees and operate as shown in Figure 8.
 4)  The scan pattern may enter the PWS mode only during the takeoff and approach modes of operation when the WXR has not been selected by the flight crew amd the PWS is automatically activated. The scan is shortened from | 90 to | 45 degrees and operates as described in Figure 8.
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2300 FT PWS AUTOMATIC ACTIVATION AIRPLANE IN AIR WITH RADIO ALTIMETER < 2300 FT 1200 FT
PWS ALERTS ENABLED WITH RADIO ALTIMETER < 1200 FT
400 FT
PWS CAUTIONS INHIBITED WITH RADIO ALTIMETER < 400 FT
50 FT
PWS WARNINGS INHIBITED WITH RADIO ALTIMETER < 50 FT RUNWAY GROUND
WARNING 
INHIBIT 
100  50 
KTS  FT 
CAUTION INHIBIT 
80 KTS  400 FT 

TAKEOFF
2300 FT
PWS AUTOMATIC ACTIVATION
AIRPLANE IN AIR WHEN
　
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