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Predictive Windshear Inputs

These are the inputs to the WXR R/T for predictive windshear (PWS):

Ground proximity warning system inhibit discrete

Auto throttle 1 switch pack throttle position discrete

Auto throttle 2 switch pack throttle position discrete

Radio altimeter 1 and 2.


The GPWS determines the priority for the aural warnings and cautions to the flight compartment. If the PWS CPU finds there is a windshear condition, the WXR R/T sends the warning or caution to the GPWS.

The auto throttle packs determine the position of the throttles. When the airplane is on the ground and either throttle is moved more than 53 degrees, the PWS comes on automatically.

The PWS CPU uses the radio altimeter input to turn the PWS on or off. When the airplane goes below 2300 feet radio altitude on approach, the PWS is turned on. When the altitude goes above 2300 feet during takeoff, the PWS is turned off.

Antenna Control

The WXR R/T gets attitude data for antenna stabilization from the ADIRUs. When the IRS select switch on the navigation/ displays source select panel is in NORMAL or BOTH ON L, the R/T uses the left ADIRU for stabilization. You put the IRS select switch to BOTH ON R to change to the right ADIRU stabilization data. The IRS select switch sends a ground discrete to the WXR R/T.

WXR Central Processor Unit

The WXR central processor unit (CPU) uses the control data to control the operation of the R/T and the antenna drive. The CPU sends these control signals to the transmitter circuits:





Also, the WXR CPU makes the scan and elevation signals from the ADIRU attitude data. It sends these signals to the antenna for antenna stabilization. The WXR CPU also gets antenna position signals from the antenna assembly.

Predictive Windshear Central Processor Unit

The PWS CPU uses inputs from these systems to turn on the WXR PWS function:

Auto throttle switch packs

Radio altimeters.


The PWS CPU controls the antenna scan and pulse repetition frequency of the transmitter to detect windshear events directly in front of the airplane. The area is limited to a very small range because of the high pulse repetition frequency.

When the PWS CPU detects a windshear, it sends the warning or caution to the GPWS. The GPWS has the priority logic for warnings and cautions. If there is no higher priority warning or caution, the PWS CPU sends the windshear display to the DEUs and sends the aural signal to the REU. Also, the PWS CPU sends an aural inhibit to the TCAS computer to inhibit any aural signals from TCAS.

Oscillator/Transmitter Circuits

The oscillator/transmitter circuit makes RF pulse patterns and sends them out through the WXR antenna.

RF Transmit


The RF pulses go from the transmitter circuits through the circulator. The circulator connects the antenna to the transmitter during RF transmission. It also connects the

antenna to the receiver circuits to get the return RF pulses.

From the circulator, the RF goes to the WXR antenna.

RF Receive

The antenna receives the RF return signals. Then the RF goes through the circulator to the receiver circuits. The receiver circuits process the return signals and send them to the CPU. The CPU uses the strength of the RF return signals to calculate the intensity of the precipitation and to make the WXR display data.

When the PWS is on, the return signals may also contain windshear information. The PWS CPU processes the windshear returns and makes the aural signals and display signals.

WXR Display Data

The CPU puts this data into the ARINC 453 format:

WXR display data

Range processed

System mode

Status data.


The CPU sends the output data to the ARINC 453 transmitters. The 453 transmitters send the data on the high speed ARINC 453 DATA BUS 1 and DATA BUS 2 to the DEUs.

System Status Data

The BITE module continuously gets system status data. The system status and the faults show on the ND alert lines.



Date: 2016-01-14; view: 1043

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