ILS capture and tracking

[henrik.bergvin]

When you capture a localizer in APPR FMS and go to APPR LOC1, the autopilot makes exaggerated turns to intercept the localizer.

Example:
EGPH ILS for RW06. Vectors in, and was placed on a heading of roughly 90 degrees to intercept. Selected APPR FMS when I was approximately 5 miles from the CI06 and it armed APPR LOC correctly. The course for the approach is 61 degrees, and that gives me approximately 30 degrees on the intercept. My scenery has the actual localizer at 64 degrees.

When the FMS captured the LOC beam at CI06, it proceeded to turn with a 15 degree bank toward a heading of approximately 110 before attempting to capture the localizer. This image was snapped as soon as I realized it turned right and overshot the approach.


After this it made a sharp left turn (didn't note the bank, but most probably 15 left, maybe more) toward a heading of approximately 55 degrees, overshot again.

It did not get to a form of stability until approximately 3 mile final.

I've got the tracked flight path in this screenshot:


It is at the APPR LOC1 point it started with a right turn. I expect these shenanigans when coming in at an intercept of more than 50 degrees, but not something as shallow as 30. It is like it is turning directly toward the needle.

Steps to reproduce: Come in at 4000ft, 90 degree heading toward CI06 at EGPH, calm weather, arm APPR FMS at ~5nm, and let the aircraft attempt to intercept the ILS.

[tcarter.67]

I too found the autopilot ils capture to be poor. Slow to respond with intercept angles less than 30 degrees from correct course results in overshoots under almost all circumstances.
I was told by the developer that my speed was too high and that the ils capture is straight out of P3D - not custom coded. You should be able to capture the ils easily at around 180kias but I was told that was far too high.
Given that this aircraft is flown into many busy primary airports around the world. ATC would normally ask you to keep your speed up until late final for sequencing and not be too happy with you at 8-10 DME puddling along at 130 or 140 kias.
This default P3D ils capture difficult to accept as the default the ils aircraft seems to work almost too correctly - as if it’s on rails. I don’t expect it to just instantly snap into capture but it is very slow resulting in overshoots the majority of the time and does in my opinion let this amazing product down a little.
My hope is the developers will look into this issue as it should do better than it does and would continue to polish what is generally an outstanding product.

[henrik.bergvin]

Having updated to 1.2, I thought I would give it a swing to see if it was any better at tracking the ILSs, but alas it is still making exaggerated turns no matter the intercept angle.

As you can see in the screenshot here, it flies through the waypoint OGRAS, makes a high bank turn toward XIKLA, overshoots and it wobbles forth and back there.



I should note that i enabled APPR mode about 1nm before OGRAS, and my speed was 160kts (mandatory to 4 DME on this approach)

Edit: The first approach I cancelled and made a sharp left turn (the dashed line going off to the left), but the second approach had the wide overshoots.

[Slayer]

I've asked the developers for input on this. Waiting for a reply.

[henrik.bergvin]

I've asked the developers for input on this. Waiting for a reply.

Thank you, I hope it can be resolved, because it is the only thing I find lacking in this addon. I *did* have a weird thing with vnav modes starting to "flicker" on final descent to the ILS intercepts one flight, but I have yet to reproduce that. I'll make sure I have recording software ready in case it happens again.

[henrik.bergvin]

I did another test flight today just to demonstrate how things behave, and I managed to catch the flickering modes (valtpath,valt,alts,path blinking rapidly), starting roughly at 45 seconds into the video.

In addition, I can demonstrate how poorly the ILS tracking is on a perfectly normal ILS approach (ENGM, ILS 01L, VALPU transition). This just isn't acceptable in my opinion, not for an addon costing $80. I'm not stable on the lateral path until roughly 2.5nm out!

Chart for the approach:


In the video below, I am on purpose flying slowly once it should have intercepted the ILS, but the turn on to the ILS is roughly 165kts. The approach is mandatory 160kts until 4dme, but with that I would be so much off the lateral course that I'd have to go around.
https://www.youtube.com/watch?v=2w92O-QdPRQ

This is the track from Little Navmap (blue line is approach, dashed is actual path.


I should note, this is a fresh install of the 1.2 version - uninstalled the old one via control panel, removed the folder in simobjects, repaired MVAMS during the install process.

[Slayer]

Thanks for the feedback. One of the developers has responded and said he does see some overshoot on this specific approach but not all, some perform better. A revision will done but I cannot give you a timeline at this point.

[henrik.bergvin]

Thanks for the feedback. One of the developers has responded and said he does see some overshoot on this specific approach but not all, some perform better. A revision will done but I cannot give you a timeline at this point.

Thanks, hope it can be resolved. Did they also look at the weirdness with mode cycling? ~45 seconds in the video.

[Slayer]

Saw what you are talking about on video. I have yet to see this happen.
Is this reproducible? If so can you give the flight plan and location where you see this behavior?

Are you using any external utilities or mods to manipulate the autopilot?

[henrik.bergvin]

Saw what you are talking about on video. I have yet to see this happen.
Is this reproducible? If so can you give the flight plan and location where you see this behavior?

Are you using any external utilities or mods to manipulate the autopilot?

Nothing external. Plan was super simple, ENGM to ENGM, GRM and VALPU as a waypoints in that order, then I added the ILS approach to 01L. I approached VALPU at 5000ft and 220kt at an intercept angle of roughly 100 degrees on LNAV with VNAV enabled shortly after.

It happened on the first attempt at that particular approach, as well as the try that I caught on video. I've been quite put off and haven't flown more in the KA since.

Edit: With "nothing external" I mean nothing that mess with the autopilot. I have ActiveSky, Little Navmap, Rex EnvironmentForce. I also have RealTurb, but none of these modify the autopilot in any way, they just add weather effects, or are pure map/textures..