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Like all modern radar systems, the RDR-4B operates by emitting short intense pulses of microwave energy which are reflected by objects having reflective characteristics within the range of the system.  The reflected signals are processed to produce visual displays that are representative of the size, intensity, bearing and distance of the targets.  The RDR-4B incorporates an advanced microprocessor design which utilizes the Doppler principle to identify areas of moderate and higher turbulence as well as low level windshear (microburst) activity.  The RDR-4B system is designed to operate in the windshear mode automatically any time the aircraft is below 1500' AGL, at least one engine is running, and the transponder is not in OFF or STBY, REGARDLESS OF RADAR MODE SELECTED.  The system also operates in the windshear mode below 1500' AGL using an alternate scan technique if the radar is operating in any mode (WX / TURB, WX, MAP). The windshear mode is activated at 2300' AGL. However, no alerts or displays are annunciated above 1500' AGL (See Figure 3).
WARNING: Failure to return the transponder to STBY after landing or selecting any mode except STBY prior to leaving the ramp area allows the radar to operate in the windshear mode creating a radiation hazard to personnel on the ground.  The RDR-4B radiation hazard area extends 13.4 feet from the radar antenna in a 120 degree arc left and right of the aircraft centerline. This hazard exists even if the radar mode is selected OFF or TEST.
RDR-4B System Operation
General
The RDR-4B radar system operates in the same way as previous radar systems installed in Continental aircraft for weather and mapping modes.
Windshear Mode
The Windshear mode is intended to be transparent to the pilot unless an alert occurs.  The windshear mode is activated any time the aircraft is below 1500' AGL, at least one engine is operating, and the transponder is not OFF or STBY.
The system will generate 3 levels of alerts when it detects hazardous windshear activity in front of the aircraft.  The level of the alert (warning, caution or advisory) is dependent on several factors including actual altitude, phase of flight (landing or takeoff) and proximity to the windshear event.  All levels of windshear alert are inhibited on the ground above 100 KIAS until 50' AGL.
The areas covered, the level of alert generated and warnings associated with each are presented in the following table and illustrations.
Advisory  Caution  Warning 
VISUAL  ICON  ICON and Amber Lamps.  ICON and Red Lamps. 
AURAL  NONE  Chimes  Take Off: "WINDSHEAR AHEAD, WINDSHEAR AHEAD" Landing: "GO AROUND, WINDSHEAR AHEAD" 

WINDSHEAR VISUAL AND AURAL MESSAGES
Note:  Although the windshear mode is intended to be transparent unless an alert is generated, the crew may notice that the radar update rate is delayed when both radar and windshear modes are active.  This delay of up to 12 seconds is caused by the sharing of antenna and processing between the weather and windshear modes in an alternate scan technique.
Alternate Scan
When the radar is operated in a weather mode and the conditions for windshear mode operation are satisfied, the radar switches to the alternate scan function.  In an alternate scan operation, the radar uses one sweep for radar mode, the next sweep for windshear mode.  On the radar sweep, gain and tilt are controlled by the settings in the flight deck.  On the windshear sweep gain and tilt is automatically set by the R/T units programming for optimum windshear detection.
Maximum Permissible Exposure Level (MPEL)
In order to avoid the envelope in which the radiation level may exceed the
U.S. Government standard of 10 milliwatt per square centimeter, all personnel should remain beyond the distance indicated in the illustration below.  The distance to the MPEL boundary is determined by calculating the near field/far field intersection per FAA Advisory Circular 20-68B.

MPEL BOUNDARY
Caution:  Failure to place the transponder to ALT ON, TA or TA/RA prior to taking the runway will prevent operation of the radar in the windshear mode unless the radar is selected to an active mode.

2,300
1,500
1,200
Aircraft Altitude (Feet AGL)
365
50
The windshear icon shown on the screen represent size and location. Windshear is detected 2 miles ahead and slightly to the right.

0.5
1.5 3.0
5.0 Range (NM)
*Warning (Takeoff) Caution (Landing)

*Note:  During final approach the RDR-4B provides automatic range scaling to prevent aural and visual warnings and alerts beyond the touchdown zone of the runway.
MD804180
Controls And Indicators
General
The RDR-4B system controls and indicators consist of a radar indicator with integral controls, system annunciator lights, and an aural warning speaker.
　
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