ATR cannot maintain the glideslope

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Are you using Developer Mode or made changes in it?

No

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N\A

Which aircraft are you reporting an issue about? (Please also add the proper tag for it)

ATR 72

Brief description of the issue:

Aircraft goes over 1 dot below glideslope on the ILS

Provide Screenshot(s)/video(s) of the issue encountered:

Detailed steps to reproduce the issue encountered:

intercept and fly an ILS, then monitor the aircraft attempt to maintain the glideslope. App flown at VAPP +10

PC specs and/or peripheral set up if relevant:

xboxx default controller

Build Version # when you first started experiencing this issue:

1.20

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Do you have the same issue if you follow the OP’s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

2

Is it similar to this

ATR strange VNAV behaviour - Bug Reports / Aircraft & Systems - Microsoft Flight Simulator Forums

3

Probably an issue with the autopilot PID’s in the file “ai.cfg”.

4

RNAV/RNP approaches need fixing with the VPATH as well.

1 Like
5

Did one RNAV yet and it went all correct.

6

I am having the issue with not holding the glideslope. It captures fine and follows for a short distance, but then just slowly starts to fall behind the dot as it goes. If I don’t intervene by turning off the autopilot and flying the approach manually, I will eventually hit the ground.

This needs to be addressed. This is some basic stuff!

7

Does that change if you add more power?

8

Nope. I’m already trying at Vapp+10!

9

I was thinking more like full throttle, or at least until something different happens. I was thinking along the lines of the AP not being able to trim fast enough. If you can hand fly it without issue, then it sounds like an AP issue, and that seems to end up being an issue with the PID’s in the “ai.cfg” file.

Adding power might assist with this. Not suggesting you come in at full throttle for anything other than a diagnostic step, but if you find the AP can hold the approach at a certain speed, but not lower, then it may be the PID’s.

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That’s interesting. I have no idea what PIDs are, or what an AI configuration file could possibly have to do with this issue, but I do appreciate your interest. I am trying some flights now to see what power changes might do. Also checking to make sure the landing weight is what the FMC thinks it is when it calculates Vapp.

1 Like
11

They are values that are used to tweak a feedback loop.

My understanding of this is that you have a target value for say pitch, the autopilot makes a small change from where it is currently to where it has to get to, this change is evaluated, and further changes are made until the current value matches the target. This can lead to undershoot or overshoot, and the loop evaluates the output, and makes continuous changes until the target is reached.

It’s possible that the AP is struggling to match the desired pitch, at a given airspeed. If you can fly it by hand, then you haven’t run out of trim, so it may be that the AP cannot reach the desired pitch or trim by itself for “reasons”.

I found a cool little simulator for these a while back:

http://grauonline.de/alexwww/ardumower/pid/pid.html

12

I maintained 140 IAS until 1000 ft with it still 1 dot low by then no way I would trust it in IMC to minimums

1 Like
13

What’s normal Vapp, ~100kts? If the ATR can only be bought from the MP, then I don’t think there is any way to access the “ai.cfg”. What I would have done is find a plane of comparable specs, which has no problem maintaining the glide path, and transplant some of its PID values across, then re-test.

At a guess, I would say it was this one:

https://docs.flightsimulator.com/html/Content_Configuration/SimObjects/Aircraft_SimO/AI_Config_Definition.htm#glideSlopePID

14

I guess I have to object to the notion of us users having to modify the plane to make something as basic as glideslope following work properly. What I would rather see is an acknowledgement of the issue from the vendor, and an update released in a timely manner to fix it.

15

I would say I would object if we had to fix it because it had been abandoned by the developer. But I don’t object to investigating the issue, coming up with a fix or workaround, and passing that on to the developer to confirm, and implement.

I’m not averse to the very act of tinkering with something is what I’m saying.

16

Impossible for us who are xpoxed im afraid.

1 Like
17

Yeah, I appreciate that. It’s really up to the developer to fix MP issues. That’s one reason why I tend to avoid those planes unless there is no other choice.

18

Back in the fs98 days I would have had it sussed by now but we’re stuck with MP offerings or nothing hence we are quite ‘xpoxed’. I just want it fixed for the bad weather.

19

Yeah, this is one of the many known issues. Fortunately the workaround is easy. Click on the ALT button. The plane will level off. As soon as the diamond is back in the right spot, click on the APP button again to continue following the GS. You may need to click the APP button twice.

Usually the plane will not have another chance to sink below the glidescope.

Doesn’t happen every time by the way.

20

Do you have the same issue if you follow the OP’s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

i have the same problem in the both the ATR 42 & 72 fly the glidescope roughly 150-200 feet below the glidescope. Tested with empty community folder at 3 locations with both versions. EGJJ ILS26, EGTE ILS 26, EGFF ILS 30Y. Standard pressure so that’s not the problem either.