Has anyone noticed odd ILS LNAV issues?

I typically use the PC-12 on FSEconomy and fly in and out of KBNA as my round-trip hub. Last night there was pretty poor visibility preventing what is almost always a visual approach. I did 6 roundtrip legs into KBNA via ILS 31.

• I'm using v2 with GTN 750
• Default KBNA scenery
• 111.95 in NAV1
• Autopilot set to NAV
• 316* on the course
• Switch from GPS NAV to HDG
• Set VLOC on the GTN 750

I'll set capture angle within 15 degrees and the HSI will reflect the course and GS. However instead of capturing the expected course the plane will make a near 90 degree left turn. It's always a left turn. After the first time it happened I then set 111.95 in the NAV2 just in case there was some funkiness there. I have a single GTN 750 set to COM1/NAV1.

It did this 3 out of 6 approaches last night. So I know it works but I can't explain why it only works 50% of the time. I did not have these issues with V1.

Anyone else notice odd ILS capture performance?

I had tucked this in on another thread but it's probably gotten lost.

Update:

It's now about 50/50 on ILS captures. I did two landings at KSTL last night on 30L and one was fine the second it made a near 90 degree left turn on glide slope capture. Used the ILS frequency data (111.5) with 302* in the course.

Note: I do not have Bert's v2 mods currently configured on this aircraft.

I always use APR not NAV when making an ILS approach and it seems to work fine, will try KBNA. Is it only with KBNA you have this problem with?

Cheers

Martin

Martin,

I primarily fly in and out of KBNA (with FSE) but I flew into KSTL twice and it worked once. This morning I flew into KCLT (only once) and it made the 90 degree left turn again.

I also typically use APR but my understanding is that mode only handles VNAV functionality, not LNAV as well.

Thanks!

APR should handle any approach depending on what nav source is selected by the GTN. Select VLOC for ILS and GPS for RNAV. NAV is selected to follow the flight plan.

Greg

 

 

4 hours ago, gregmorin said:

APR should handle any approach depending on what nav source is selected by the GTN. Select VLOC for ILS and GPS for RNAV. NAV is selected to follow the flight plan.

Greg

 

 

All good then, following the expected procedures. VLOC for ILS and GPS for RNAV

Yes, it's common for us to use NAV to capture the LOC and then later engage APR after established on the LOC, but NAV mode, especially in FS it seems, allows for a greater error and is less precise in nailing the LOC course because it's used for VOR tracking usually. APR is more "sensitive" and will do a better job in flight simulator of snagging the LOC. See if that helps.

 

:-)

Revisiting this as I've been able to 'reproduce' the problem intermittently.

I've noticed that when I start up the aircraft the default NAV mode on the 750 is either GPS or VLOC. Typically if I have a problem on the flight with an ILS capture it's when the 750 starts up with VLOC. I typically don't navigate VOR-to-VOR so I'll change it to GPS for the flight.

So my question continues (based on the attached screenshot)

In that photo I'm flying a heading out about 60 degrees, following the GPS course. Typically the HSI when set to GPS will have the course pointing "due north" visually and usually align with my heading. In this case it's about 140 degrees but you can see on the backup gauges to the left it's aligning properly. Ultimately the HSI is reflecting the correct heading but whenever it's pointing (again visually) to the left or right) when it tries to capture the VLOC signal that's usually when things go sideways (quite literally) on me.

Does that make sense? I realize I've probably not used the correct deflection terminology, apologies on that.

 

An example (on a different flight, after restarting the sim when GPS was the default NAV load on the 750. All of the gauges line up with the expected degree track and that "due north" pointing on the GPS I mentioned earlier.

hi, I am new to this forum, but I will try to help to answer your question. on the first photo, you are left side of your track. (CDI is showing fly to the right so my position is to the left. now when you are in GPS/nav mode it doesn't matter what course you select on HSI. The HSI/CDI (course deviation indicator) is only showing you what is your deflection (track error) to you intended track derive from GPS not what you have set on HSI as your course line. When you look close on GPS it does show you fly to the right, same as HSI (same information). If you want to use OBS, VOR, ILS, LOC that is a different game as you are selecting course to be flown on HSI not commanded by GPS, there for you must select correct course to be flown. (actual difference between selected course on HSI (desire track) and your aircraft position represented by CDI- course deviation indicator.   Well second photo is correcting as well, you are right on track, there for CDI is centered. If you select different course, CDI would be still centered. For a course selector, I think it comes down to your personal preference if you have it in (Auto sync course or not) for better orientation. I like to select course manually as it helps to remember which way I am turning.

That's all to it. Hope that was what you were asking for.

Cheers Petr

 

Thanks for your response Peter.

The issue was fixed with Bert's response from this thread - https://www.avsim.com/forums/topic/509550-ehsi-primarysecondary-sync/

On 5/25/2017 at 8:38 AM, softreset said:

Thanks for your response Peter.

The issue was fixed with Bert's response from this thread - https://www.avsim.com/forums/topic/509550-ehsi-primarysecondary-sync/

Or change to a more realistic gyro in the aircraft.cfg change

https://www.avsim.com/forums/topic/453506-ehsi-gyro-drift/#comment-3182367