2 minutes ago, Fiorentoni said:

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 the current aircraft altitude it could very well be the exact amount, if the aircraft is still a bit above the FAF altitude when you look at the distance.

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.

That is actually a pretty darn good theory! I've tried so many different ways of figuring this out, there have been a few that would have made sense in theory but didn't pan out. I think this one has a good chance of being correct. How weird would that be?

Edited January 24, 20242 yr by mryan75

4 minutes ago, Fiorentoni said:

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.

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.

That would also explain why the glideslope jumps up or down when you hit approach waypoints - if you're high or low as you reach a waypoint, it will affect the distance.

I really like this theory. Time to test!

1 hour ago, mryan75 said:

It flew the ILS just fine.

What were you checking?

 

1 hour ago, vonmar said:

What were you checking?

 

Flew the ILS10 at TTPP. It doesn’t hold glideslope on RNAV approaches, the vertical guidance is all over the place. So I wanted to see if it could fly an ILS. 

11 minutes ago, mryan75 said:

Flew the ILS10 at TTPP. It doesn’t hold glideslope on RNAV approaches, the vertical guidance is all over the place. So I wanted to see if it could fly an ILS. 

What were you checking on the ILS approach?

9 hours ago, vonmar said:

What were you checking on the ILS approach?

Whether it would follow the glide path (it did) and if the distances on the approach would be correct (they were not). 

5 hours ago, mryan75 said:

Whether it would follow the glide path (it did) and if the distances on the approach would be correct (they were not). 

Now that you know the ATR has DME.

Did you check the ATR's DME distances at all approach fixes against the ILS approach plate?

Did you check ground distances between fixes on the ILS approach plate against the DME distances?

Maybe do a screenshot showing the problem.

Note:

Previously you were reporting problems with TNCC .

Did you check the ATR's ILS DME distances at TNCC?

 

 

 

 

 

55 minutes ago, vonmar said:

Now that you know the ATR has DME

I find this comment more than a bit snide. We were talking a GPS approach before, where whether the ATR had DME or not was completely irrelevant. I more than once edited a reply to you in order to reign in how tiresome the DME bit had gotten. Apparently you weren't finished. I, however, am. 

Blocked. Goodbye.

Edited January 25, 20242 yr by mryan75

On 1/22/2024 at 4:26 PM, mryan75 said:

Well unfortunately this issue has not been fixed:

I get incorrect and inconsistent distances from the FAF to the RW waypoint on RNAV approaches every time. Was just flying the RNP11 to TNCC, from the FAF (ELUVA) it is supposed to be 6.0 NM to the RW11 threshold; it was 6.4 NM. Yesterday I flew the RNAV10 approach to TTPP, from the FAF (TALUS) to the RW10 waypoint is supposed to be 5.1 miles, it was 5.8 NM. Same thing at TAPA a few days ago, the distance from the 40THR (which literally means "4.0 NM to the threshold of the runway"), the distance was 4.5 NM.

Just frustrated beyond belief at this. The release notes for this version cryptically said "DME distance calculation issue corrected". Notwithstanding the fact that this aircraft doesn't even have DME, I assumed that this is what they were talking about and had fixed it. Clearly they have not.

So unfortunately for me this is now a VFR-only aircraft. Which effectively renders it completely pointless.

You were first to mention DME and you were frustrated, so I wanted to follow up.

"Just frustrated beyond belief at this. The release notes for this version cryptically said "DME distance calculation issue corrected". Notwithstanding the fact that this aircraft doesn't even have DME, I assumed that this is what they were talking about and had fixed it. Clearly they have not."

As I recall I was the one who later mentioned the RNAV approach you were looking at was not DME:

In your last test you mentioned ILS distance problems .... so I asked you to provide specific for information.

Not just for me but for outer users as well.

 

By defenition distances between waypoints in a RNAV approach are always as straigh-line horizontal distances, just like the DME distances in an ILS approach which is also normalized to the straight-line horizontal distance.

They differ because the reference points are different too: threshold vs DME equipment placement.

I've just came to this part of the ATR thread and wasn't aware of the bug(?) but, so..., do you mean that in all aircraft using the default GNS equipment the RNAV distances are slant-based instead of straight-line ?

 

4 hours ago, jcomm said:

I've just came to this part of the ATR thread and wasn't aware of the bug(?) but, so..., do you mean that in all aircraft using the default GNS equipment the RNAV distances are slant-based instead of straight-line ?

The only thing I can say for sure is that in literally every other aircraft, the distances on whichever nav equipment you’re using match the distances on the charts. In the ATR they’re off literally every single time. I just can’t figure out why and where the distances in the ATR are coming from. It’s always the distance from the last fix before the runway fix to the runway fix (if there is one of course). It’s off every single time on any approach of any kind. It’s bizarre. It seemingly flies ILS approaches just fine now, whereas prior to the update it did not. But following the guidance on RNAV approaches is all over the place. Sometimes it brings you down short of the runway, sometimes halfway down the runway. 

Edited January 26, 20242 yr by mryan75

5 hours ago, jcomm said:

I've just came to this part of the ATR thread and wasn't aware of the bug(?) but, so..., do you mean that in all aircraft using the default GNS equipment the RNAV distances are slant-based instead of straight-line ?

No, in the default aircraft the distances appear to be fine.

In the ATR, the only distance that appears to be affected is the distance from the last waypoint before the threshold to the threshold. But whatever the ATR is calculating, it doesn't appear to be slant range. Going back to the first example that @mryan75 gave, the RNP RWY 11 at TNCC. The distance from ELUVA (the FAF) to the threshold is supposed to be 6.0 nm according to the chart. The ATR reports the distance as 6.4 nm. But this cannot be explained by slant range.

Let's calculate what the slant range from ELUVA to the threshold would be, using the Pythagorean theorem. The crossing height for ELUVA is 2000 feet. The airport elevation is 36 feet, the TCH is 50 feet. In other words, from ELUVA to the threshold is a vertical distance of 1914 feet, or 0.32 nm. The horizontal distance, as noted above, is 6.0 nm. Using the Pythagorean theorem, we obtain a slant distance of sqrt(6.0^2 + 0.32^2) = 6.01 nm. In other words, just a tiny bit more than the horizontal distance, and certainly not enough to explain the 6.4 nm displayed by the ATR.

 

1 hour ago, mryan75 said:

But following the guidance on RNAV approaches is all over the place. Sometimes it brings you down short of the runway, sometimes halfway down the runway. 

This is an interesting observation. From this, it sounds as if not just the distance displayed is wrong, but that the ATR is actually navigating to an incorrect position.

If you follow the RNP RWY 11 guidance at TNCC all the way down to 50 feet AAL, where do you end up? Is it about 0.4 nm past the threshold? If so, that would mean that the distance the ATR displays is consistent with the vertical guidance -- it's just using the wrong position for the waypoint.

Edited January 26, 20242 yr by martinboehme

24 minutes ago, martinboehme said:

If you follow the RNP RWY 11 guidance at TNCC all the way down to 50 feet AAL, where do you end up? Is it about 0.4 nm past the threshold?

In this particular case it brought to the threshold of the physical runway, in other words the start of the displaced threshold. I remember because I had to add power and fly the length of the displaced threshold at 20 feet AGL before plopping it down on the runway. Prior to the update I know that at several airports (TJSJ being one) where it would take you roughly halfway down the runway. So they did change something, I’m just not sure what. 

I honestly give up on trying to figure this airplane out. Just flew the ILS 09Z into TBPB, it captured localizer and glideslope (albeit about 0.4 NM early on the GS capture), followed it down, went below the GS even though it was captured, never did anything to correct, and would have easily put me down about 2 miles short of the runway.

On 1/24/2024 at 11:21 PM, btacon said:

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

-B

There is a poet, t'wich may not know it! 😄