ILS approach not working

[jlaspden]

I bought A2A C172 on 12 May 2019. I installed Accu-Sim Update 02/04/2019 last week. Since the update, the ILS approach is not working. I mean lateral guidance. Runway heading is very misaligned. Today I was flying to Gardermoen (ENGM), ILS 1L 110.30. Autopilot approach is about 2 miles east of runway 1L.
C172 is configured no GPS.
I'm using FSX SE, Windows 10 64-bit.

[Nick - A2A]

Hello jlaspden and welcome to the A2A forums.

Are you using any add-on scenery for ENGM? Misaligned or offset ILSes are typically down to errors in the scenery BGLs. I checked, and with the default FSX-SE scenery, the OBW ILS is aligned correctly.

Thanks,
Nick

[jlaspden]

I'm using Orbx Norway. I have the same problem for the USA with the default FSX-SE scenery.

[Nick - A2A]

Do you mean you have the same problem with each ILS approach you try in FSX? If so, please can you confirm if you've tried the same approach with a default aircraft?

Thanks,
Nick

[jlaspden]

I flew from ENBR to ENGM via DRA VOR 114.80, about 196 NM (weather theme Building Storms) A2A C172, the same result as before.
I flew from ENBR to ENGM via DRA VOR 114.80 (weather theme Building Storms) default C172, perfect approach.
I flew from ENBR to ENGM via DRA VOR 114.80 (weather theme Clear Skies) A2A C172, the same result as before.
I flew from ENRK to ENGM, about 50 NM (weather theme Fair Weather) A2A C172, very good approach.

[jlaspden]

I've flown only short flights before the update. Possibly the problem is not about an update.

[Nick - A2A]

Yes, the issue is unlikely to be related to the update as nothing has been changed with regard to the avionics in the 172.

Please can you try to clarify exactly what it is that doesn't seem to be working for you. You describe lateral guidance as being "misaligned", but you also mention using the autopilot.

Is the CDI (course deviation indicator) on the VOR1 gauge centred when you're on the extended centreline of the runway?

If so, is the issue basically that the autopilot in APP mode isn't behaving as you expect it to?

Thanks,
Nick

[jlaspden]

The CDI on the VOR1 gauge centred when I'm on the extended centreline of the runway.
The autopilot in APP mode and NAV mode isn't behaving as I expect it to.

[Paughco]

The NAV/GPS toggle is set to "NAV," right? There are lots of good videos about this on YouTube: Here's a really basic one, where the pilot get the ILS lined up, then hand flies the airplane in: https://www.youtube.com/watch?v=UXuEI5JQDBc . Here's one with an A2A 172 and the guy uses the autopilot. He's starting out above the glideslope which is not so great, but it's pretty close to what we're looking for (OK, he's pitching down): https://www.youtube.com/watch?v=RRDwKE2YBlE. Nope, he's still hand flying it.

The way I do it is pretty much like this: I've got the ILS frequency active in to NAV 1, and the OBS needle set to the runway heading. I'm flying with the autopilot in NAV mode, at a reasonable altitude to intercept the glideslope, flying at an approximate 45 degree angle to the glide slope, a few miles out from the runway. When the vertical needle on the OBS starts to move from full deflection towards the center, I engage the APR button on the autopilot. The airplane is supposed to line up with the ILS, and then start descending when the glideslope needle reaches the center. Same as the videos, but "otto pilot" is doing all the work.

Another really fun video is this one by SIM CFI: https://www.youtube.com/watch?v=RqTHSRV ... 82BzdiVe4l.

Seeya
ATB

[Nick - A2A]

Okay, thanks for the clarification. If the issue is with the autopilot rather than the ILS guidance itself, that gives us a much better idea of where to look.

Paughco's question is certainly a good place to start.

If the GPS/NAV switch is already in the NAV position, please can you give us a rough idea of the framerate you're seeing in the sim? If FPS drops below around 18, then you're quite likely to encounter instability when it comes to some of the autopilot functions.

However, if performance on your system is in the 20's or above, the issue may lie with how you're using the autopilot. Can you let us know how far you are from the runway threshold when you're intercepting the ILS, and what sort of intercept angle you're using? Also, which autopilot lateral mode are you using prior to switching to APP mode?

A screenshot showing your track or one-or-two from the cockpit at the point of intercept would probably help to diagnose the issue too. There's some more info on attaching images here.

Cheers,
Nick

[jlaspden]

NAV/GPS switch is on NAV.
Frame rate is 19.9.
Autopilot is HDG mode before I switch APP mode.
I select APP mode about 23 NM from the runway threshold. Intercept angle is about 55 degrees.
When I select APP mode, aircraft turns right about 90 degrees from the runway heading. Then it turns left intercepting the ILS.

[Nick - A2A]

Okay, thanks for the info jlaspden. It's possible that low FPS could be the culprit here, unless you're certain it's always around the 20 mark or higher?

However, are you adjusting the heading bug on the DG to agree with the desired approach course? (Usually this is the runway heading.) Unless you do this, the autopilot won't be able to calculate the correct intercept course to fly.

Thanks,
Nick

[jlaspden]

Thank you for the help, Nick.
I read the manual for KAP 140. I did not understand the instructions for the ILS approach.
I followed your advice of the setting heading bug on runway heading. Perfect approach.
John

[Nick - A2A]

Thanks for the update John. Sounds like adjusting the heading bug to agree with the desired course was all that was needed, although the FPS issue is worth keeping in mind.

As regards the autopilot manual, there's a small (5 page) summary of the KAP 140 operation that I unearthed on the internet a while ago. It's perhaps a bit more digestible than the full thing. The link subsequently died, but you can download a copy from the link below:

Honeywell KAP 140 Two Axis with Altitude Preselect Autopilot

If you have any more questions though, we'll do our best to answer them.

Kind regards,
Nick