(c)
Weather and windshear scan pattern, with windshear event detected When the system is placed into alternate weather/windshear scan pattern and the system detects a windshear event, the antenna scan pattern is as follows:
-clockwise weather scan, from minus 90 deg. to plus 90 deg.
-counterclockwise windshear scan, from plus 90 deg. to minus 45 deg., with windshear processing between plus 45 deg. and minus 45 deg.
-the next clockwise scan is from minus 45 deg. to plus 45 deg. to validate windshear
R 1EFF : 001-049, 101-105, 151-199, 1 34-41-00Page 44 1 1 Config-3 May 01/05 1 1 1CES 1
WR/PWS - Logic of scanning mode
Figure 009
R 1EFF : 001-049, 101-105, 151-199, 1 34-41-00Page 45 1 1 Config-3 May 01/05 1 1 1CES 1
-the next counterclockwise scan is from plus 45 deg. to minus 90 deg. to validate windshear. No processing occurs between plus 45 deg. and minus 90 deg.
-clockwise WX scan, from minus 90 deg. to plus 90 deg. The sequence is repeated as long as windshear event is detected. If a windshear event is not detected, the system reverts to the alternating weather/windshear scan pattern described above. The refresh rate of the WX image is minimum 16 sesonds due to sharing processing between radar and windshear event detection.
(d) Windshear scan pattern When the system operates in windshear mode only, the scan pattern is plus or minus 45 deg. azimuth coverage on both the clockwise and counterclockwise scans. This mode occurs if the operator has placed the weather radar to OFF mode. Windshear data are processed during both directions of antenna scanning. In this case the windshear mode works transparent to the flight crew until a windshear event is detected. The refresh rate of the display is 8 seconds.
R **ON A/C 051-099, 106-149, 201-299, 301-399, 401-499,
A. Operation
(1) Weather Radar modes The weather radar system uses the principle of radio echoing. It works at a normal frequency of 9333 MHz. The peak power emitted is 120 W approx. The weather radar transceiver generates microwave energy in the form of electromagnetic pulses via an X-band wave guide to the antenna. When these pulses intercept an appropriate target, part of the energy is reflected back to the weather radar antenna then to the transceiver. For each case, the system uses a different mode of operation which allows to vary the scanning of the antenna, the timing of the pulses and the processing of the weather radar returns and of the predictive windshear events (if the function is activated). The electronics circuits of the transceiver measure the elapsed time between the transmission of the wave and the reception of the echo to determine the target distance (it takes around 12.36 microseconds for the electromagnetic wave to travel out and back for each nautical mile of target range). The angular position of the target is detected by the angular position of the antenna in its scanning in azimuth. As the quantity of energy reflected to the antenna is proportional to the target
1EFF : ALL 1 34-41-00Page 46 1 1 Config-3 Aug 01/05 1 1 1CES 1 density, the different levels of atmospheric disturbances (see table 1 below) are shown on the displays by different colors. The detection of the turbulence areas are based on the Doppler phenomenon.
--------------------------------------------------------------------------| LEVEL DETECTED | PRECIPITATION RATE | COLOR OF ECHOES | |------------------------|-----------------------|-----------------------| | Z1 < 20 dBz | less than 1 mm/h | black | | 20 less than or equal | from 1 to 4 mm/h | green | | to Z2 < 30 dBz | | | | 30 less than or equal | from 4 to 12 mm/h | yellow | | to Z3 < 40 dBz | | | | 40 less than or equal | 12 mm/h and above | red | | to Z4/Z5 < 50 dBz | | | |------------------------|-----------------------|-----------------------| | Turbulence | 5 m/s | magenta | -------------------------------------------------------------------------|
Table 1: Color Correspondence Table
(2) Windshear mode (if the predictive windshear function is activated) The WR/PWS, by a doppler mode, determines the wind field ahead of the aircraft. By a mathematical treatment, the system determines the hazard factor (so-called "F factor") related to the danger of a windshear event. An hazard factor exceeding a value of 0.13 and within 5NM ahead of the aircraft is considered as the presence of a dangerous event and a corresponding windshear alert is generated. The display of windshear hazard consits of an icon of red and black bands superimposed on the radar returns. As these events are dangerous during takeoff and landing maneuvers, the PWS mode is automatically activated below 2300 ft radio altimeter and at least one of the qualifier-A and one qualifier-B inputs have to be valid. Windshear detection operates automatically with the above-mentioned reasons, even if the radar function selector switch is set to OFF, but windshear switch has to be set to AUTO. The windshear mode is transparent to the pilot until a windshear event is detected. When a windshear event is detected, the system generates the appropriate annunciations (visual and aural) to the flight crew. The WR/PWS generates a graphic symbol (icon) to the displays indicating where the windshear was detected. The windshear function detection can operate either with weather radar modes activated or independently without these modes. If the radar is already operating in a weather detection mode when a windshear is detected, no pilot intervention will be required.
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