Just now, martinboehme said:

I first thought it might be computing the distance to the runway midpoint rather than the threshold, but runway 11 at TNCC is longer than two times 0.4 nm.

Maybe it's computing the distance to the ARP? Should be relatively easy to check... if you create a leg from ELUVA to TNCC, how long is that leg? 

That's exactly what I was thinking, the runway is longer than 0.4NM times two. But I'm glad I brought it up here. First of all, that's exactly my thought, that it's telling you the distance to the ARP. But I wasn't clever enough to think of creating a leg from ELUVA to TNCC, that's a brilliant idea. I will have to check that. Thanks so much for the brainpower!

Just checked, but no... apparently a leg from ELUVA to TNCC is 7.3 nm (according to the GNS 430 in the default 172).

Real ATR Pilot Tests MSFS - YouTube

FWIW...

2 hours ago, martinboehme said:

Just checked, but no... apparently a leg from ELUVA to TNCC is 7.3 nm (according to the GNS 430 in the default 172).

It gets even weirder. I checked the procedure in Little Navmap. Using Navigraph Data I get a distance of 5.6NM between Eluva and RW11 (THR11). On the map that it is apparent why that is. The waypoint for RW11 is misplaced in the data. It is at the start of the Runway. If I measure the distance to the displaced Threshhold with the ruler tool in Little Navmap I get the missing 0.4NM for 6NM.

That still does not explain why the default Garmins have the correct distance and the ATR has too much and why Little Navmap has too little.

Edited January 23, 20242 yr by Farlis

I think the last few posts about DME have gotten into an accidental pedantic realm between actual DME receivers and "distance measured" (by a GPS or IRS source).  

Vonmar was hooked deeply into the physical DME receiver, when quoting slant angles, etc.  But there are no slant angles with GPS/IRS calculated distances.

And the fact was, mryan was correct - the quoted distances on the ATR's PFD are always off.

Edited January 24, 20242 yr by JYW

43 minutes ago, JYW said:

I think the last few posts about DME have gotten into an accidental pedantic realm between actual DME receivers and "distance measured" (by a GPS or IRS source).  

None of what we're discussing here is about DME -- it's all RNAV. Indeed, there is no DME station at either of the waypoints in question (ELUVA and the runway 11 displaced threshold at TNCC). And the ATR is displaying an incorrect distance between those two waypoints (6.4 nm instead of 6 nm).

(Maybe this is what you meant -- but I wanted people to be clear that DME doesn't enter into the picture at all.)

16 hours ago, Farlis said:

It gets even weirder. I checked the procedure in Little Navmap. Using Navigraph Data I get a distance of 5.6NM between Eluva and RW11 (THR11). On the map that it is apparent why that is. The waypoint for RW11 is misplaced in the data. It is at the start of the Runway. If I measure the distance to the displaced Threshhold with the ruler tool in Little Navmap I get the missing 0.4NM for 6NM.

I don't think the waypoint for RW11 is necessarily misplaced. You do need a waypoint for the non-displaced threshold, for when you're departing from that runway.

I believe it's possible for approach procedures to code waypoints that aren't otherwise accessible by name outside of that approach procedure. I suspect that this is how the displaced threshold is coded; it doesn't need to be provided as a "standalone" waypoint because there is no need to use it outside of an approach procedure. I assume the non-displaced threshold does exist as a standalone waypoint because you need it when departing from that runway (and you might not be departing on a SID, so the non-displaced threshold can't be coded merely as a waypoint that is "internal" to the SID).

Edit: As to the question of why the ATR is displaying the wrong distance -- could it be that the ATR's distance calculations are just generally wrong? Has someone checked with a two enroute waypoints and compared against the result from another source?

Edited January 24, 20242 yr by martinboehme

2 hours ago, martinboehme said:

I don't think the waypoint for RW11 is necessarily misplaced.

I'm not sure. I checked the overlay option in Navigraph charts with the georefenced Approach Chart on the world map. And that puts THR11 clearly at the start of the displaced threshhold and not at the start of the runway.

Currently flying a route that will end in an ILS approach, we'll see how that goes.

@martinboehme you've had some really valuable input here, thank you. I will check some of the waypoints on my route against the chart.

Edit: Well, from SHARK to TRI on both the Jepp chart and in Little Navmap is 11.2 NM, in the ATR's FMC its 11. From TRI to RW10 on the chart and LNM is 4.2 NM, in the ATR it's 5.0 NM. All the distances between the other waypoints in the flightplan are correct.

So in reality from SHARK to RW10 it's 15.4 NM, in the ATR it's showing 16. The question is why.

It would be great if someone could post this in the official forums, I got thrown out. 😲

Edited January 24, 20242 yr by mryan75

 

please delete post

Edited January 24, 20242 yr by Flori747

2 hours ago, mryan75 said:

Well, from SHARK to TRI on both the Jepp chart and in Little Navmap is 11.2 NM, in the ATR's FMC its 11. From TRI to RW10 on the chart and LNM is 4.2 NM, in the ATR it's 5.0 NM. All the distances between the other waypoints in the flightplan are correct.

I just did a test of my own with some enroute waypoints, and the distances I get in the ATR check out against what Navigraph shows me. So it looks as if the ATR has an issue specifically with runway waypoints.

Interestingly, I note that runway 10 at TTPP doesn't have a displaced threshold -- so the problem occurs not only with displaced thresholds.

32 minutes ago, martinboehme said:

I just did a test of my own with some enroute waypoints, and the distances I get in the ATR check out against what Navigraph shows me. So it looks as if the ATR has an issue specifically with runway waypoints.

Interestingly, I note that runway 10 at TTPP doesn't have a displaced threshold -- so the problem occurs not only with displaced thresholds.

Yep, I've come to the same conclusion. Whatever it is always happens between the final waypoint before the RW waypoint (if there is one) and the RW waypoint itself. I'm literally astounded nobody has brought this up in the official forums yet.

8 hours ago, martinboehme said:

None of what we're discussing here is about DME -- it's all RNAV. Indeed, there is no DME station at either of the waypoints in question (ELUVA and the runway 11 displaced threshold at TNCC). And the ATR is displaying an incorrect distance between those two waypoints (6.4 nm instead of 6 nm).

(Maybe this is what you meant -- but I wanted people to be clear that DME doesn't enter into the picture at all.)

Yes, that's exactly what I was saying.    The discussion got stuck in semantics.

15 minutes ago, JYW said:

Yes, that's exactly what I was saying.    The discussion got stuck in semantics.

If the discussion is about Semantics , it will surely become Pedantic! 😎

-B

It flew the ILS just fine.

Could it be that the (MSFS) ATR does not measure the distance in a horizontal line but does include the vertical distance, i.e. the current altitude? As for the example mentioned here: The 0.4nm difference make for about 2400 feet, which is not that far off from the 2000 feet FAF altitude. Similarly SHARK is about 4000 feet above the threshold and the ATR gives 0.6 more nm than in reality (which again amount to about 3700 feet).
It's not the exact amount, but it's close. If it really uses the current aircraft altitude it could very well be the exact amount, if the aircraft is bit above or below the FAF altitude when you look at the distance.
EDIT: The small difference could also be caused by the ATR using the STD pressure altitude for that (wrongly added) vertical distance and not the actual BARO altitude.

This would also only happen on RW navpoints, because they have a native/physical altitude, while other waypoints don't have a fixed altitude. One could test this, I guess, by flying at 20000 feet over the airport and see what distance the ATR measures to the runway navpoint.

Edited January 25, 20242 yr by Fiorentoni