"Too low, Terrain"

[jalexb88]

I have a small issue in the 2 past flight I did (I'm using PSX 10.159 & Navigraph cycle 2211). Just under ~200 feet before the flare I get a "Too low, Terrain" from the EGPWS, I got this both on an ILS 27L into EGLL and ILS 29L into VIDP. The approach is loaded into the FMC from its database and the aircraft is perfectly on profile so I don't think this alert should happen... Is it a database issue? I included the 2 situ files where it happens for me.

https://www.dropbox.com/s/wb7p2oof74l1r4j/EGLL_27L.situ?dl=0

https://www.dropbox.com/s/znel9ci5gphbzsa/VIDP_29L.situ?dl=0

Cheers, Alex

EDIT: Aha! I feel a little dumb for posting this because I just remembered that I set a dual GPS failure on those 2 flights... I just re-flew those situ with the failures fixed and no alert...I imagine the DME updating was not enough to keep the EGPWS happy on those approaches after 10+ hour (oceanic) flights.

[Hardy Heinlin]

Radio updating is a function of the FMC. It's one of several methods of the FMC to compute the present position. The EGPWS terrain warning system, however, doesn't use any FMC computed position. The EGPWS is independent of the FMC. The EGPWS gets position data directly from the GPS units, and if both units fail, the EGPWS gets position data directly from the left IRU.

If you select the POS display on the EFIS control, you see the three white stars of the three IRU positions on the ND. You'll see they have drifted a lot. So the EGPWS is thinking you're flying into terrain.


Regards,

|-|ardy

[jalexb88]

That makes sense, thanks!

Alex