SRS guidance after reactive Wind Shear

[Microburst2002]

Hi mates

I've been looking at the Wind Shear thing and I don't fully understand how the SRS behaves after the wind shear is detected (by the reactive ws detector).

Imagine we are on a take off, speed is V2 plus 10 kt or so, pitch about 15º, rate about 2,000 fpm, then all of a sudden we hear the "wind shear wind shear" auto call out. Speed has gone 20 kt below and the trend is going down, rate falls to 300 fpm only.

What command will the pitch bar give exactly?

The FCOM says that in all engine operating, SRS will give command for V2+10 kt, with maximum pitch 22.5º and minimum rate of 120 fpm in the A320 (a gradient of 0.5% in the A330). Oh, and a speed protection limiting the target speed to to V2 + 15. That is a lot of things in the same mode. So what will happen according to that?

Perhaps a pitch down to go for V2 + 10 until rate goes below 120 fpm, then increase the pitch as required to maintain that rate regardless of speed, until maximum 22.5º up, then maintain this pitch until AP disconnect, then until full aft sidestick?

the pitch down thing is what does not seem right to me.

Anyone out there who knows exactly how it goes?

[vilas]

Microburst2002
The FD guidance you have stated is the normal behaviour of SRS mode. However if you read DSC-22_40-40 P 1/2 the SRS has modified behaviour in wind shear conditions. Stated below:
"In wind shear conditions, flight guidance acts on specially adapted FD pitch orders received from the speed reference system (SRS). The pilot must set go around thrust immediately (which also triggers the FD SRS mode), and follow the pitch order to execute the optimum escape maneuver".
So as long as you are in SRS you can safely fly the SRS to get out of wind shear. But the real problem is when THR RED/ACC ALT is low something like 800ft AGL. Because now LVR CLB will flash while still in wind shear which off course you should ignore but the SRS will also change to CLB. The flight guidance no longer will modify the FDs for wind shear conditions and aircraft will pitch down to accelerate to initial climb speed. This can be dangerous. If WS conditions still exist you need to ignore FDs and fly 17.5 or even full back stick if needed to keep climbing out of wind shear.

[latetonite]

Don't you have a reactive wind-shear procedure for your aeroplane? Or is this nowadays also automatic?

[Microburst2002]

Vilas

thank you for that.

The CLB mode activation is not a nice thing. Just as the SRS has a special guidance, why didn't they change that?

[Microburst2002]

Anyone can further explain in what consist the special guidance provided by SRS when in wind shear?

[Goldenrivett]

The CLB mode activation is not a nice thing..... why didn't they change that?
Windshear warning is available until 1300 ft agl. Default AA is 1500 ft. So if the operator reduces AA below 1500 ft, then it is one of the consequences they should consider.

[vilas]

Microburst
What Golden rivet states is correct Airbus does not recommend lowering of ACC ALT below 1500ft. However in your original post when you stated SRS pitch to maximum 22.5° you missed out on wind shear condition. It is 18° in normal and 22.5 in WS conditions. This guidance also comes from FAC. AP disconnects when speed drops below Valpha prot.