GypsyPilot
Mohawk Town
Here is some info on the sink rate call which you will get in mode 1 of the EGPWS with the gear and flaps down:
The “SINK RATE” alert is based on altitude and initiated when the rate of descent exceeds the
following approximate values:
Altitude (AGL) Descent Rate (FPM)
500 1500
400 1400
300 1300
200 1200
100 1000
If the rate of descent exceeds these values by an additional margin, the EGPWS will initiate the
“PULL UP” warning. A go-around following the “PULL UP” aural warning is mandatory.
Looking at Gypsy's PDF, if your high descent rate worsens, it looks like you'd get a "pull up" call at 1600 fpm at 100 feet while 1000 fpm will get you "sink rate".
According to the LOC 18 into BHM, it has a 3.28 degree glide path. Let's round that to 3.3 degrees. Then, look at page 11 of 13 of the descent rate PDF here:
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC 120-108.pdf
Looks like you need 876 fpm to stay on path. You get a "sink rate" call at 1000 fpm at 100 agl.
My point with all this is that at very low altitudes you have little margin between required descent rates and the EGPWS saying "sink rate". To get a "Pull up" you need 1600 fpm at 100 feet. Just throwing all that out. I've got "sink rate" a few times on approach and corrected. It's not good but it's correctable.
I'm not trying to speculate. Just throwing out some interesting numbers that show the challenge of a non-precision approach at typical high heavy jet airspeeds. Be safe.....
Thanks for the info. One thing I would add, and I preface this by saying I have no idea what kind of EGPWS was on that plane. But with the GPWS referenced in that PDF, an airplane in the landing configuration would be in mode 2b, and the "Pull-up" aural alerts would be suppressed. The only 2b alerts would be "Terrain, Terrain!" if the terrain closure rate envelope was exceeded.