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A couple of issues with EGPWS terrain (display)

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Hi all,


I have spent quite a few hours with the PMDG 777 now and I am still delighted by this magnificient aircraft. So first of all, it's time to say thanks from my side for creating this impressive simulation. 


On of the aspects I really love about the latest PMDG aircraft is the EGPWS simulation. Back, in old Aerowinx PS1 days, I made myself familiar with loads of technical details on EGPWS and I still love this system. That's why I would like to discuss a few things I noticed. I think I found two bugs and a few things which do not "feel" correct. Read on for more, please.


1) First of all, let me start with an issue I found comparing the PMDG 777 EGPWS display with real world photos (simulating them in PMDG). Generally, the 777 compares very well but:


This particular image shows the first issue quite well - note the high and low values from the PEAKS MODE display just below the TERR announciation.

(Numbers 143 and 000). You might remember: this indicates the highest (14.300') and lowest terrain points shown on the ND.





Now, let's switch off the Water Display in CYAN:




Note that the figure indicating the lowest terrain figure on the ND terrain display has changed from 000 to 072, indicating the lowest terrain point has an elevation of 7.200'.


I think, there is a bug - namely the value showing 000 with water display turned on.  Whenever Water in CYAN is switched on and water is visible the lowest terrain value is 000. This is not correct.


While I understand this from software programmers point of view - the lowest point IS indeed  000 (and shown in blue) - it does not make sense from the EGPWS logic point of view - the pilot is still interested in the terrain and not in the sea level elevation. In the real world, even with sea level water in CYAN display, the aircraft shows 073 on the peaks mode display, see here. (My apologies for showing an Airbus cockpit. :lol:  ).




Of course, you'll note the excellent agreement between simulation (PMDG) and real world (Honeywell EGPWS). By the way, the position shown in the images should be obvious.



2) My second "bug" results from pure chance and not from systematic observation.  :P Recently I was flying the ILS34 approach into Wellington, New Zealand (NZWN) (before Wordlflight 2013 and during WF.) 


Two issues here: on the approach, I got a spurious TERRAIN PULL UP warning and an obviously incorrect terrain display. To demonstrate this, I'll show a couple of screenshots from the approach on the ILS34.


First image: on ILS34, at 560', 1.8 DME out.

You can already see that I have received a PULL UP warning although I am well established on the ILS. This may be something worth looking into - the warning is false.

But notice - again - the SEA WATER display in CYAN is on and shown correctly.





Second Image: A few seconds later, on the ILS at 0.4 DME and 110'. I still have the TERRAIN message and the PULL UP warning on the PDF, but notice that

the sea level display in CYAN is gone and replaced by all yellow colour. 


This is clearly not correct.




Just to show that the incorrect 'all yellow' display of the sea level is not related to the TERRAIN message, here is the ND during taxi into the ramp. Again, sea level display in CYAN is not shown were it should be shown.





Okay, this concludes my first section on things where I think that something is wrong. 



3) In this third section, I will show a few things where I think that the EGPWS terrain display is not entirely correct. But is more like a "feeling" - I cannot really prove nor do I have images or documentation to show that something is wrong.


I initially discovered this next issues while flying on airway L888 from KCA in Western China towards SANLI. This is an airway which runs directly across the Tibetian plateau over terrain of typically 15.000' or more (with peaks up to 20.000') and with sector minimum altitudes in the 25.000' to 29.000' range. 



Approaching LUVAR intersection, I noticed this display by the EGPWS computer.




Now, this looks strange to me because:

- it clearly shows that EGPWS is in a PEAKS MODE display (only green)

- the highest terrain figure (198) indicated the highest terrain of 19.800' is clearly well below the airplane cruising at FL370

- the terrain elevation below the aircraft is about 14.500' (and not 107)

- and the display is all green


This is very confusing to the pilot and kind of violates the principle of the EGPWS Peaks Mode display to show only the highest peak elevations (e.g. mountain tops) around and not flat terrain. From a situational awareness point of view, this does not look correct.


As far as I know, there is no image anywhere in the literature, on the web, in a DVD/Blueway which shows an all green terrain display from EGPWS (from WX radar of course, but not from EGPWS).


My feeling is that a lowest terrain elevation of something like 15.500' would be more appropriate and thus show peaks only.


The bottom line of this section is: I think that an entirely green EGPWS terrain display is not shown on a real world aircraft.





Obviously, this image changes when the ND range is changed and I could continue showing images with different ranges. It looks better and different with a high ND range, but with a low (10 or 20 NM) ND range, I again get an all green display. There is probably no point in showing these images.


Just one for the moment being... the issue of an all green display is not limited to the special case of flying along airway L888 over Tibet. Earlier on the same flight, around LASDO intersection (N46.5, E076 in Kazakhstan), I noticed a similar behaviour over essentially flat terrain. Here the low figure is 1100' (011) and the high figure is 1500' (015) of PEAKS display, which is basically a very flat desert.




Or another example (without image), the same behaviour (all green) over flat terrain over Argentina, just 10 miles west of RYD VOR (approx. S34, W065). 



To conclude, I think that I have found a few issues within the EGPWS terrain display of the 777 (and possibly the 737NGX; my forum search has shown a similar post for the 737). I would appreciate some feedback, possibly from PMDG as well and wonder if this could be adressed in any upcoming service update for this great aircraft.


Thanks a lot,







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