Reactive wind-shear A320
 

On the B737, Reactive wind-shear was a function of the EGPWS. While the A320 FCOM states WINDSHEAR DETECTION FUNCTION is done by the FAC.

How does the FAC help in windshear detection & how is it different from what the EGPWS does on the B737.

Also why does the FAC need to calculate GW in flight. Why won't it take it from the FMS as in the 737 for calculation of speeds.

FAC judges windshear from the AOA. Once beyond threshold it triggers wind shear warning. Also it raises the FD range to 21.5° instead usual 17.5°. What happens in Boeing not for me to say.

People have taken off with FMC weight tens of tons different from the actual weight.

On the A320 and I have to believe the 737 for regulatory reaons

EGPWS is just GPWS with a terrain database isn't it. It compares GPS position and altitude against what the terrain database says.

Reactive Windshear warning uses aircraft sensors to trigger the alert when the aircraft is in a windshear.

Predictive windshear is based upon Weather Radar system detecting shifts in microwave pulses from the aircraft.

On the A319/320 the FACs generate a windshear warning whenever the aircraft's predicted energy level falls below a predetermined threshold.

On our 319/320’s we have EGPWS however the windshear warning is a basic GPWS function (Modes 1-6 and windshear) It is not an EGPWS function. It could your company enabled (paid for) EGPWS mode 7 an advanced windshear warning function which the EGPWS generates.

This is a very good explanation:

Mark V and Mark VII EGPWS Pilot's Guide

https://skybrary.aero/bookshelf/books/3364.pdf

From what I have gathered so far is, the A320 does not have the reactive windshear warning generated via the EGPWS (mode 7), but via the FAC. On the B737 Windshear warning is generated by the EGPWS, it not optional.

This mentioned in the Mark V and Mark VII EGPWS Pilot's Guide shared by Captain Mongo.EGPWS windshear is provided for certain (not all) aircraft.

The 737 doesn't have any computers capable of assessing the aircraft energy state / flight path so the job is offloaded to the GPWS system. I imagine it was a convenient decision to hand the problem to Honeywell (or [insert manufacturer here]) than try to implement it themselves.

The FACs already have the job of continuously calculating energy state on the A320 series so adding a reactive windshear warning is trivial. I'm not convinced that windshear detection is based solely on AoA; instead the FAC is monitoring the total energy of the aircraft and if that drops below a predefined level than a reactive windshear warning is triggered.

From FCOM:
The FACs generate the windshear warning whenever the predicted energy level for the aircraft falls below a predetermined threshold. In computing this energy level prediction, the FACs use data from different sources. From ADIRS comes data such as vertical speed, air and ground speeds and slope ; from other sources come such derived parameters as total slope, longitudinal wind gradient, and vertical wind. The FACs express this energy level as an angle of attack and compare it with an angle-of-attack threshold above which windshear conditions are most likely and pilot action is required

If you’re lucky enough to be in and remain in SRS during W/S you get 22.5 degrees.

It would almost make sense to set ACCEL altitude to 1500’ when implementing W/S takeoff precautions to ensure one remained in SRS during the threat from W/S.

Wouldn’t you say Vilas?

yes absolutely! In such cases Airbus also recommends higher acceleration altitude like normal noise abetment 3000ft.

We had that discussion several years ago and it looks like your persistence with Airbus paid off - well done.

When did that change? Could you be so kind to post a screen shot of the FCOM stating that?

Thanks.

CaptainMongo

It's not in the FCOM. It was a reply from Airbus to my question.

Captain Mongo
Here it is what Vilas is alluding to


22-22-40
WINDSHEAR DETECTION PRINCIPLES
Applicable to: ALLThe FACs generate the windshear warning whenever the predicted energy level for the aircraft falls below a predetermined threshold.

In computing this energy level prediction, the FACs use data from different sources. From ADIRS comes data such as vertical speed, air and ground speeds and slope ; from other sources come such derived parameters as total slope, longitudinal wind gradient, and vertical wind.

The FACs express this energy level as an angle of attack and compare it with an angle-of-attack threshold above which windshear conditions are most likely and pilot action is required.