(8)
AIRPLANES WITH PREDICTIVE WINDSHEAR ACTIVE; The radar returns received by the radar receiver are digitized and fowarded to the navigation displays in binary format. In addition, these radar returns are processed with WXR interface data in the WXR R/T to determine if there is a windshear event in front of the airplane. If a windshear event is within the caution or warning regions in front of the airplane, various annunciations and aural messages are sent to the navigation displays and other crew cabin components. Windshear is a threat to the airplane during takeoff and in the early phase of climb out as well as during the final phases of approach. See Fig. 3.
(9)
The video signal received by the radar receiver is digitized and fowarded to the navigation displays in binary format.
(10)
When weather radar MAP mode is selected, the weather radar system operates in the terrain mapping mode. Rotating the GAIN control out of AUTO position toward MAX causes the noise and video in the display to increase. Varying the GAIN control setting in the map mode may increase the definition of certain types of terrain targets.
(11)
In the WX/TURB mode, normal weather detection is displayed in green, yellow and red at all ranges with the turbulence returns within 40 miles displayed in magenta.
C. Functional Description
(1) Electrical Power and System On/Off Control Circuits
(a)
The weather radar system receives the following power for operation. The left and right R/Ts receive 115-volt, 400 Hz, ac power from the circuit breakers on the P7 overhead circuit breaker panel. The antenna receives 115-volt ac power from the antenna stabilization and drive circuits in the R/T.
(b)
The left and right weather radar system may be turned on with the captain's or first officer's EFIS control panel WXR switch/indicator. The system on/off signal from the EFIS microprocessor goes through the weather radar control panel mode select switch and system transfer switch to either the left or right R/T. This discrete ground on/off signal enables the selected R/T which generates power supply voltages of 12 and 28 volts dc for the control panel.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 747-400 MAINTENANCE MANUAL
REACTIVE WINDSHEAR ALERTS BELOW 1500 FT AGL
Predictive Windshear Operation
Figure 3
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ú 13 ú BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. Page 20Feb 18/02
K03085
A
747-400
MAINTENANCE MANUAL
(c)
The left or right R/T provides 12 or 28 volt dc to the weather radar control panel left or right power supplies and system transfer switch contacts. The left system 28 volts dc at the normally closed contacts of the system transfer switch is sent to the R/T microprocssor through the de-energized contacts of the waveguide switch. When the right R/T is selected on the control panel, a discrete ground is sent to the left R/T which stops transmitting. The right system 28 volts de-energizes the waveguide switch to connect the right R/T to the antenna and sends 28 volt dc to the right R/T microprocessor to start rf transmission.
(d)
The captains and first officer's NDs are enabled to display weather radar data when the WXR switch/indicator on each EFIS control panel is placed to on. These enable signals are sent through the left and right CDUs on the display control and range data busses to the NDs. The left CDU controls weather data on the captain's ND and the right CDU controls weather data on the first officer's ND.
(e)
When the left or right EFIS control panel is inoperative the respective ND loses the ND enable signal from the CDU. In order to restore the weather radar display to the ND an alternate enable command can be generated using the appropriate CDU. Refer to Integrated Display System (AMM 31-61-00).
(2) Automatic Turn-on Operation
(a)
Turn-on of the windshear mode is automatic. Power is applied from the R/T circuit breakers to the left and right receiver/transmitter. Turn-on is possible even if the WXR switch on the EFIS control panels are in the off position.
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