Wxr system - nd range disagreement General

The DEUs compare the ND ranges from these components:

• EFIS CP

• WXR R/T

• Flight management computer (FMC).

A difference between any of these ranges causes an amber range disagreement message on alert line 3.

These WXR range disagreement messages are possible:

• WXR RANGE DISAGREE; shows when there is a difference between the EFIS CP range and the WXR R/T range

• MAP/WXR RANGE DISAGREE; shows when there is a difference between the EFIS CP range, the WXR R/T range, and the FMC range.

WXR RANGE DISAGREE will show in these modes:

• Expanded approach

• Expanded VOR

• Expanded map

• Centered map.

MAP/WXR RANGE DISAGREE will show in these modes:

• Expanded map

• Centered map.

This happens during a range disagreement:

• WXR display goes out of view

• mode, tilt, and gain messages show

• FMC range shows.

Wxr system - wxr r/t functional description General

The WXR R/T makes RF pulses and sends them to the antenna. The antenna transmits pulses and receives the return signals and sends them to the WXR R/T. The R/T processes the return signals to make display data that shows on the NDs. The WXR data on the ND shows the weather patterns in front of the airplane.

The WXR R/T also comes on automatically during take off and approach to detect windshear events in front of the airplane. If a windshear event is detected, the WXR sends cautions or warnings to the flight compartment.

Control Inputs

The EFIS control panel (EFIS CP) sends the WXR system ON/ OFF discrete on a digital bus to the display electronics unit (DEU). The DEU sends a discrete to the WXR R/T to turn ON the weather radar. The discrete goes through the WXR control panel to ensure the panel is in the airplane. The DEUs only send the ON discrete if the navigation display is in the correct mode. The EFIS CP sends range data to the WXR R/T.

The WXR control panel sends control data on a bus to the WXR R/T. The WXR CP sends these signals:

• Gain

• Tilt

• Mode of operation.

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.