WXR system - power and analog interfaces

System Power and ON/OFF

The WXR receiver transmitter (R/T) gets 115v ac through the WXR RT circuit breaker from the 115v ac XFR BUS 2 (P6 circuit breaker panel). The WXR R/T circuit breaker also sends 115v ac to the WXR R/T mount for fan operation.

The left and right EFIS control panels (CP) send the ON/OFF data to display electronics unit (DEU) 1 and DEU 2. The DEUs make sure the navigation display is in a mode that can show WXR data. If the navigation display is in a correct mode, the DEUs send an ON/OFF discrete to the WXR control panel. The ON/OFF discrete goes through the WXR control panel to the WXR R/T. This discrete lets the WXR R/T operate.

When the WXR R/T gets the ON signal, it sends 28v dc to the power supply in the WXR control panel and 115v ac to the WXR R/T power supply.

The WXR R/T sends a 28v dc power interlock to the WXR control panel. The control panel sends the 28v dc interlock back to the WXR R/T as R/T ENABLE.

The WXR antenna gets 115v ac from the WXR R/T.

The WXR RT mount gets 115v ac from XFR bus 2 for fan test power. This permits an operational test of the fan when the RT is not installed.

Discretes

The GPWS sends an inhibit discrete to the PWS. The discrete inhibits PWS aural alerts if the GPWS alerts are a higher priority.

The PWS aural alert will stop when a higher GPWS alert is received.

The landing gear lever sends a landing gear down discrete to enable PWS during an approach.

The left and right auto throttle switch packs send discretes (QFR A) to enable the PWS function. When the throttles move through 53 degrees and the aircraft is below 2300 feet RA, the radar turns on.

The audio inhibit discrete goes to the TCAS. The TCAS uses this discrete to downgrade all RAs to TAs and inhibit all aural alerts.

RF Transmission and Reception

Transmit radio frequency (RF) goes from the R/T through the waveguide to the weather radar antenna. The receive RF goes from the antenna through the waveguide to the R/T.

WXR SYSTEM - CONTROL AND DISPLAY INTERFACE

Digital Inputs

The WXR R/T receives data from these systems:

· Air data inertial reference system (ADIRS)

· Radio altimeter (RA) system

· Common display system (CDS).

 

Air Data Inertial Reference System

The ADIRS sends this inertial reference (IR) data to the WXR R/ T on a high-speed ARINC 429 data bus:

· Pitch angle

· Roll angle

· Groundspeed

· True heading

· Magnetic heading

· Drift angle

· Discretes.

 

The WXR R/T uses the IR data for windshear calculation, sensitivity time control (STC), and stabilization.

The ADIRS sends this air data (AD) to the WXR R/T on a lowspeed ARINC 429 data bus:

· Uncorrected baro altitude

· Corrected baro altitude

· True airspeed

· Computed airspeed.

The WXR R/T uses altitude and airspeed data for windshear calculation. The WXR R/T also uses altitude data for sensitivity time control calculations.

Radio Altimeter System

The radio altimeters send radio altitude on a low-speed ARINC 429 data bus to the WXR R/T for the predictive windshear (PWS) function. The PWS uses this data to do these functions:

· Turn PWS on and off

· Enable/disable display and alert functions.

 

Common Display System

The EFIS control panels send range data and the WXR on/off discrete to the display electronic units (DEUs) on an ARINC 429 data bus.

The DEUs send range data from the EFIS control panel to the WXR R/T on ARINC 429 data buses. The DEUs send the WXR on/off discrete to the WXR control panel on a discrete wire.

Control Inputs

The WXR control panel supplies this data to the WXR R/T:

· Transmit mode

· Tilt

· Gain control

· On/off discrete.

 

WXR Output Data and Display

The WXR R/T sends display data on an ARINC 453 data bus to the terrain weather relays. The display data goes from the terrain weather relays to the DEUs to show on the navigation displays. The terrain/weather radar relays are controlled by the ground proximity warning computer (GPWC).

The WXR R/T sends windshear alert data on an ARINC 708A hazard bus to the ground proximity warning system (GPWS). The GPWS uses this data to prioritize alert callouts. If a higher GPWS alert exists, the GPWC switches the terrain weather relays and terrain data is shown on the NDs.

 

 

 

WXR SYSTEM - PWS INTERFACES

General Description

The predictive windshear (PWS) part of the weather radar (WXR) system interfaces with other airplane systems and components.