Airbus Predictive Winshear.
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Airbus Predictive Windshear.
I'm after more info. on the way that predicitive windshear, PWS, works. (Rather than the Airbus standard FAC sensed windshear)
Obviously it's radar sensed but does it need water droplets to work? On our a/c when the system is turned on you get a radar tilt indication, but only on the ground. Thus I assume that the tilt is critical and that flying around with +10 deg isn't going to help your PWS detection!
Any more info greatfully received!
Obviously it's radar sensed but does it need water droplets to work? On our a/c when the system is turned on you get a radar tilt indication, but only on the ground. Thus I assume that the tilt is critical and that flying around with +10 deg isn't going to help your PWS detection!
Any more info greatfully received!
Last edited by Wander; 29th Oct 2002 at 06:17.
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First of all, the PWS sweeps at 0° no matter what the radar tilt indication says. The indication appears only to remind the pilots, that the aircraft radar is emitting. Which it does as soon as PWS is switched on (even on ground).
PWS needs moisture of some kind to operade. Not sure though if it has to be droplets or if haze of some sort would suffice.
Through the return data of this moisture it can determine wind direcion and velocity for a short range of airspace in front of the aircraft. Sudden changes in either will result in a warning.
I've only ever had once since it's been installed - and this was a nuisance warning anyway (clearly recognizable as such).
PWS needs moisture of some kind to operade. Not sure though if it has to be droplets or if haze of some sort would suffice.
Through the return data of this moisture it can determine wind direcion and velocity for a short range of airspace in front of the aircraft. Sudden changes in either will result in a warning.
I've only ever had once since it's been installed - and this was a nuisance warning anyway (clearly recognizable as such).
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Here is some information regarding the Honeywell RDR-4B that we have installed in our A320s. So far (other than in the sim), I have only seen the windshear icon taxiing to the gate. Other pilots I have talked to, that have seen the icon, have not seen any false warnings.
According to an engineer from Collins, their PWS radar can process doppler returns from extremely low levels of rain. Well below the level required to be depicted as a green return. So it is possible for their system to detect and display windshear without any rain being displayed on the ND. I assume the same is true for the Honeywell system, but I don't have any documentation for this.The more that I learn about the efforts that went into the engineering of these PWS systems, the more respect that I have for them. I hope you find this informative.
The Kid
1. The radar sets the tilt angle for the PWS automatically to locate the center of the beam at 100 meters above the ground at 6 nmiles. If there is excessive ground clutter that interferes with the PWS detection, then the antenna tile might be increased to position the beam as high as 300 meters above the ground at 6 nmiles. These tilt settings provide the optimum detection of the outflows from the windshear. Only the selected tilt from
the control panel is displayed on the ND, not the actual tilt angle for the PWS mode.
2. The displayed tilt never changes between the PWS and other modes; since the PWS tilt is never displayed. We implemented this way to avoid tilt angle changes every other sweep.
3. The R/T is activated at 2300 ft AGL, but it does not start doing PWS immediately. First, it goes through some monitoring checks (BITE). Then, it establishes the parameters for PWS detection. Since, there is no requirement to display any PWS information until aircraft gets down to 1500 ft AGL, the data bus to the EFIS is not turned on until 1500 ft AGL. That is why you would not be seeing any tilt display above 1500 ft, although the radar is turned on at 2300 ft.
According to an engineer from Collins, their PWS radar can process doppler returns from extremely low levels of rain. Well below the level required to be depicted as a green return. So it is possible for their system to detect and display windshear without any rain being displayed on the ND. I assume the same is true for the Honeywell system, but I don't have any documentation for this.The more that I learn about the efforts that went into the engineering of these PWS systems, the more respect that I have for them. I hope you find this informative.
The Kid
1. The radar sets the tilt angle for the PWS automatically to locate the center of the beam at 100 meters above the ground at 6 nmiles. If there is excessive ground clutter that interferes with the PWS detection, then the antenna tile might be increased to position the beam as high as 300 meters above the ground at 6 nmiles. These tilt settings provide the optimum detection of the outflows from the windshear. Only the selected tilt from
the control panel is displayed on the ND, not the actual tilt angle for the PWS mode.
2. The displayed tilt never changes between the PWS and other modes; since the PWS tilt is never displayed. We implemented this way to avoid tilt angle changes every other sweep.
3. The R/T is activated at 2300 ft AGL, but it does not start doing PWS immediately. First, it goes through some monitoring checks (BITE). Then, it establishes the parameters for PWS detection. Since, there is no requirement to display any PWS information until aircraft gets down to 1500 ft AGL, the data bus to the EFIS is not turned on until 1500 ft AGL. That is why you would not be seeing any tilt display above 1500 ft, although the radar is turned on at 2300 ft.
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For those who may not be able to do the maths, 100 metres at 6NM equates to around 0.5 degrees of up tilt. 300 metres at 6NM equates to about 1.5 degrees of up tilt. This information probably won't be very helpful with the standard weather radar, though I confess to checking between 0.5 degrees up and down in flight.
That has, usually, been enough to keep me out of real trouble but, of course, not always...
It certainly isn't a substitute for the sort of thing that's being discussed here, sadly. 
That has, usually, been enough to keep me out of real trouble but, of course, not always...
It certainly isn't a substitute for the sort of thing that's being discussed here, sadly.
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The PWS tilt is kept at very low levels so that the system can detect the doppler return from a downburst. If the antenna was directed too high, the vertical component of the downburst would not be detected by doppler processing. Only after the downburst reaches the ground and is deflected from a vertical to a horizontal flow does the doppler processor have the opportunity to detect the event.
The Kid
The Kid
