737NG GPWS ("reactive") windshear alerts?

[singletracker]

Hey all...

Quick question about the 737NG's GPWS windshear alerts (not PWS).

The Boeing FCOM says this in the Warning Systems chapter:

Windshear warnings are accompanied by WINDSHEAR on the attitude indicators and voice aural alerts.
Windshear cautions are accompanied by a voice aural alert.

So am I to understand that, a windshear caution has no yellow WINDSHEAR caption on the PFD below the attitude sphere? In other words, just a "WINDSHEAR, WINDSHEAR" aural warning? Then why, during the GPWS test, do we see a flashing WINDSHEAR followed by WINDSHEAR?

Also, the FCOM has no information about what data the GPWC uses to issue the windshear alerts. I assume it's something to to with rate of change of groundspeed versus airspeed... does anyone know for sure?

[ampclamp]

single tracker, care to edit the colour?
That yellow is awful and almost impossible to read..No contrast.
Thanks.

[ImbracableCrunk]

Not much info in the FCOM, is there. Maybe it's too much info for the non-engineer.

Two independent, identical stall management yaw damper (SMYD) computers determine when stall warning is required based upon:
• alpha vane angle of attack outputs
• ADIRU outputs
• anti–ice controls
• wing configurations
• air/ground sensing
• thrust
• FMC outputs.
• mach compensation

The SMYD computers provide outputs for all stall warning to include stick shaker and signals to the pitch limit indicator and airspeed displays and the GPWS windshear detection and alert.

I'd guess it comes from at least part of the list the SMYD uses for stall detection.

[singletracker]

Hey, Boeing picked the colors, not me!
Edited anyway.

[grounded27]

ampclamp

It would really please me if you deleted your distasteful post.

Thanks...

[ampclamp]

grounded27

No I will not, I was being polite and the request was reasonable given it was very difficult to read.
As it is I cant help with the enquiry but was simply trying to help those who could to read the text.

Single tracker thanks.Not everyone has the same eyesight as others here.

[I Just Drive]

There's more posts in this thread about the posts than the thread.

I too think its not very clear about the difference between windshear cautions and warnings on the NG. Particularly as cautions can be treated as such and don't require GAs whereas warnings do.

I wonder how many people would reject the TO for 'Monitor Radar Display'.

[grounded27]

I wonder how many people would reject the TO for 'Monitor Radar Display'

You are speaking of PWS, you would not recieve a reactive alert on t/o roll.

[grounded27]

Also, the FCOM has no information about what data the GPWC uses to issue the windshear alerts. I assume it's something to to with rate of change of groundspeed versus airspeed... does anyone know for sure?

I am pretty sure it is a combination of airspeed and accelerometer imputs. Can not speak for sure about the 737 but in most type aircraft the FCC plays a large part and on a coupled approach will level wings 10 deg nose up and toga.