PMDG 737-800 capturing glideslope versus Fenix A320

[SquadronLeader 61]

Hi, I am using FSiPanel to practice landings in both the PMDG 737-800 and Fenix A320.

I usually select an airport and runway with ILS and start from a RH or LH base position.

When the Fenix A320 captures the glideslope, it banks once and lines up the runway - which is what I would expect.

What I have noticed with the PMDG 737-800 at a number of different airports - is that when it captures the glideslope, it banks once then levels up before being in line with the runway - banks a second time and levels up when in line with the runway.

So, what I am experiencing is that the Fenix A320 lines up with the runway in one smooth bank when it captures the glideslope - whilst the PMDG 737-800 is making two banks to align itself with the runway.

Thought it might be a bank angle limitation - but that is on maximum

Anyone else experiencing this? - or can explain as to why it is happening.

Cheers and Happy New Year

 

Edited December 29, 2022 by SquadronLeader

[jcomm 5,977]

It's always safer to have 2 banks instead of just one, just in case a bank/financial crisis take place...

[flyingpauls 66]

The real thing has a very advanced computation of the interception. They tried to mimic it in the simulation. You can now arm the localizer very early, and it will go to LOC * gently approaching the centerline.

[somiller 694]

There shouldn't be any bank at all to capture the GS, only pitch and power change. Are you sure you aren't talking about localizer capture?

[martinboehme 511]

Yes, pretty sure the OP is talking about the localizer.

@SquadronLeaderAt what angle are you intercepting the localizer? Standard intercept angle is 30 degrees. Larger angles can cause some aircraft to overshoot - not sure what would be realistic for the 737.

[LRBS 948]

The Airbus is a Cadillac compared to Boeing in reference to intercepts (LNAV/VNAV or LOC/GS), it will roll on/off smoothly in any mode. 

Boeing is a bit peculiar on ILS/LOC/GS intercepts and will bounce a little left/right during intercept if not at the right speed. If more than 30 degrees to intercept in a terminal area a good speed would be no more than 180, it will bounce very little.

 

Both have a pretty wide range of intercept angles up to 120 degrees.

Talking about PMDG, not a pretty picture here. Their intercepts are bad especially on ILS with large and abrupt bank angles, unfortunately not realistic at all.

They still have big issues with the LNAV and the item I mentioned plus the autopilot interface.

For some reason, this is going on for years and has still not been fixed.

[vonmar 124]

Hi SquadronLeader ,

I returned FSiPanel long time ago. It just did not work well on my setup.
So, for testing I just save the PMDG flight at various stages e.g. before LOC intersept then replay the saved flight.

Do you see the same Glide slope problem without FSIpanel in use?

Could you do a video ?

 

For testing I only have the PMDG737-600 and -700.

Have you seen the problem on other PMDG aircraft or just the -800?

Edited December 29, 2022 by vonmar

[SquadronLeader 61]

Thanks for all the responses

My mistake - I should have referenced capturing the localiser not the glideslope.

Intercepting the localiser is at an angle of approx 90 degrees - but although from the comments that is deemed to be excessive - the A320 handles it perfectly.

Note the comments that PMDG ILS intercept have room for improvement.

Onwards and upwards

[andreh 125]

There haven't been any comments on the PMDG forums that the plane has problems capturing the localizer. I have not encountered this problem myself while flying it (without FSiPlanel). There are lots of factors involved here, and there's not enough information in this thread to come to a conclusion. It could very well be that the PMDG does it realistically, while the Fenix is unrealistically agile.

Consider what speed you're making the turn. If you're too fast, you might overshoot. It could also simply be that FSiPlanel interacts with the PMDG in some way that results in this.

Edit: PMDG implemented a brand new LNAV system a few months ago so some comments made above may be outdated.

Edited December 30, 2022 by andreh

[martinboehme 511]

2 hours ago, SquadronLeader said:

Intercepting the localiser is at an angle of approx 90 degrees - but although from the comments that is deemed to be excessive - the A320 handles it perfectly.

That's definitely an excessive angle. Not sure how the real 737 behaves, but I wouldn't generally expect an autopilot to capture the localizer in this scenario without significant overshoot and one or two subsequent S turns.

Others have remarked above that the (real) A320 performs unusually well in this regard. That might explain why the Fenix does so too.

In the real world, controllers will typically give a 30 degree intercept. A 90 degree intercept would likely elicit questions or complaints from the crew. 

 

[vonmar 124]

3 hours ago, SquadronLeader said:

Thanks for all the responses

My mistake - I should have referenced capturing the localiser not the glideslope.

Intercepting the localiser is at an angle of approx 90 degrees - but although from the comments that is deemed to be excessive - the A320 handles it perfectly.

Note the comments that PMDG ILS intercept have room for improvement.

Onwards and upwards

"Intercepting the localiser is at an angle of approx 90 degrees"

Which FAA airport/approach were you testing?

[jrw4 626]

FAA policy on precision approach intercept angles is provided here:

https://tfmlearning.faa.gov/publications/atpubs/ATC/atc0509.html

It's generally 30 degrees except 20 under certain circumstances. This is not true for GPS approaches.

[LRBS 948]

4 hours ago, andreh said:

There haven't been any comments on the PMDG forums that the plane has problems capturing the localizer. I have not encountered this problem myself while flying it (without FSiPlanel). There are lots of factors involved here, and there's not enough information in this thread to come to a conclusion. It could very well be that the PMDG does it realistically, while the Fenix is unrealistically agile.

Consider what speed you're making the turn. If you're too fast, you might overshoot. It could also simply be that FSiPlanel interacts with the PMDG in some way that results in this.

Edit: PMDG implemented a brand new LNAV system a few months ago so some comments made above may be outdated.

There are a couple of issues here happening, unfortunately, if you point out some discrepancies about the product in their forum, many users, some beta testers including some in the developers' team will feel the need to dismiss any findings or play the blame game or just don't know how the real airplane should behave. Many times if you push the issue your complaints/findings will get deleted. That's your answer not seeing "comments".

 

As an airline pilot (dual qualified in Boeing and Airbus) we are talking about two different airframes with totally different systems and behaviors. What you think about Fenix of being "unrealistic agile" it is not correct, this is how the airplane reacts. Airbus systems are softer and more defined in certain aspects compared to Boeing. 

 

You are right on the money when you mentioned that speed is a factor, especially in this case "LOC intercept".

 

"Usually" when on final vectors to intercept, we are at about 180 KTS, and sometimes during capture, you will notice a slight deviation and bank correction left/right before settling down (not on Airbus). Unfortunately, PMDG has issues with not properly anticipating entering/exiting the turn translating into overshooting or undershooting and high unrealistic bank rates.

 

Regarding that PMDG implemented a brand new LNAV system is totally incorrect, they still have issues with it and is not fixed after so many years.

[andreh 125]

To the op: There are some tips and points to take in over at the pmdg forums in the identical thread you posted there. If you haven't checked it out, do so.

[LRBS 948]

1 hour ago, andreh said:

To the op: There are some tips and points to take in over at the pmdg forums in the identical thread you posted there. If you haven't checked it out, do so.

First, I would like to let you know that this is not a personal attack.

 

Actually is quite good advice, especially when FSiPanel is known on some PCs not to interact well with PMDG.

 

As you mentioned, the speed (in excess of 180 KTS) and distance to the intercept point is a factor.

 

I tried many configurations where what he is experiencing is beyond any tips, it's just superficial programming that PMDG needs to fix.

 

To elaborate more, I did a 30 degrees ILS intercept at 10 NM before the threshold, with no wind, and fully stabilized at a Vref of 145 KTS and there is the same issue.

Unfortunately, this is not the only issue with their products.