PMDG 737 RNP Approach

[Stearmandriver]

What an odd exchange.  

Here's the thing - the real plane flies these procedures ON RAILS. Literally.  Bank angle varies smoothly through a turn as necessary for wind correction but it does so as a smooth, steady change in bank angles.  Nothing is jerky, there are no oscillations, it never over-banks and corrects etc... I tried to tell them that for years on their forum. 

They act like the plane should behave the same as it does while following a radio nav aid, and that's completely wrong.  When coupled to a nav aid, all the plane can do is react to deviations from the radio nav course.  It doesn't know where it is in relation to anything, so it can't predict anything.

When the plane is flying an RNP approach, it's flying a lateral path it has already calculated all the way to the runway.  It knows exactly where it is in relation to this path at all times, it knows the current wind, it knows what the path will do next and exactly how far ahead that happens.  It knows its current speed, and the schedule on which it will slow.  It's not *reacting* to anything.  Thus, there is no jerkiness, no over corrections, and it never, ever, leaves the computed lateral path.  

No dev is perfect, and no simulation of a real thing will ever be perfect.  That's... Ok.  But it's really odd how completely unable they are to admit that at PMDG.  They seem pathologically unable to admit they've made a mistake, or that something isn't perfect but as good as they can make it. 

I still think they make some of the absolute best products in flight sim.  This attitude they insist on perpetuating isn't doing them any good though.  Especially not with something like this, where anyone can find a video of a 737 flying RNP procedures and see it behaves very differently than their product.  I mean... Why is it hard for them to just admit that?

[Bobsk8]

7 minutes ago, Stearmandriver said:

What an odd exchange.  

Here's the thing - the real plane flies these procedures ON RAILS. Literally.  Bank angle varies smoothly through a turn as necessary for wind correction but it does so as a smooth, steady change in bank angles.  Nothing is jerky, there are no oscillations, it never over-banks and corrects etc... I tried to tell them that for years on their forum. 

They act like the plane should behave the same as it does while following a radio nav aid, and that's completely wrong.  When coupled to a nav aid, all the plane can do is react to deviations from the radio nav course.  It doesn't know where it is in relation to anything, so it can't predict anything.

When the plane is flying an RNP approach, it's flying a lateral path it has already calculated all the way to the runway.  It knows exactly where it is in relation to this path at all times, it knows the current wind, it knows what the path will do next and exactly how far ahead that happens.  It knows its current speed, and the schedule on which it will slow.  It's not *reacting* to anything.  Thus, there is no jerkiness, no over corrections, and it never, ever, leaves the computed lateral path.  

No dev is perfect, and no simulation of a real thing will ever be perfect.  That's... Ok.  But it's really odd how completely unable they are to admit that at PMDG.  They seem pathologically unable to admit they've made a mistake, or that something isn't perfect but as good as they can make it. 

I still think they make some of the absolute best products in flight sim.  This attitude they insist on perpetuating isn't doing them any good though.  Especially not with something like this, where anyone can find a video of a 737 flying RNP procedures and see it behaves very differently than their product.  I mean... Why is it hard for them to just admit that?

I lost a great deal of faith in PMDG after buying the DC 6, which is still riddled with bugs, and all they say at PMDG is " We don't see any issues with it". So the result is, hardly anyone flies it anymore. I think the iFly 737 Max, when it is released in it's final stage, might replace the PMDG 737 as the most popular 737 on MSFS. 

[dusty_sourdough907]

Good morning fellas.

I too have been a long time customer of PMDG. I have to say I agree with what you have observed. It's a shame.

Not flying the DC-6 due to what's already been stated. Very little to put in the faith jar...zip really 😞 

[tfm]

It's been years now since PMDG made the sad error of starting to believe their own propaganda. That's often a point of no return. 

[jrw4]

21 minutes ago, Stearmandriver said:

It knows exactly where it is in relation to this path at all times, it knows the current wind, it knows what the path will do next and exactly how far ahead that happens.

It knows the current wind, but can it predict the future presence of variations in that wind field as it flies into it? I have never flown anything more than a 172 irl, but I recall making constant changes in flight in response to the wind. A Boeing has much greater mass and momentum than a 172, of course, but do we know how well MSFS simulates the real atmosphere's wind variability?

Many thanks to the real world pilots who contribute to this and other discussions.

[Christopher Low]

The constant criticism of PMDG from some members of the flight simulation community can be annoying at times, but this is one of those areas where I agree with them. Obviously I am not an expert on how the real world aircraft flies, but the simple fact of the matter is that those little wobbles (either at the start of a turn, or during turns) just do not feel right to me. For example, I cannot believe that a real 737 would wobble slightly to the right before initiating a turn to the left.

It reminds me of the unrealistic "bounce" that I experienced in the P3D version of the 747-400. The nose dropped rather unrealistically when the power reduced as the aircraft levelled out at an altitude restriction during departure, and proceeded to "bounce" up and down as the thrust changed. It felt very unnatural for such a large aircraft, and ultimately I stopped flying the 747 because the 777 made a much better job of it in those situations.

Edited October 23, 2024 by Christopher Low

[Maxis]

1 minute ago, Christopher Low said:

The constant criticism of PMDG from some members of the flight simulation community can be annoying at times, but this is one of those areas where I agree with them. Obviously I am not an expert on how the real world aircraft flies, but the simple fact of the matter is that those little wobbles (either at the start of a turn, or during turns) just do not feel right to me. For example, I cannot believe that a real 737 would wobble slightly to the right before initiating a turn to the left.

It reminds me of the unrealistic "bounce" that I experienced in the P3D version of the 747-400. The nose dropped rather unrealistically when the power reduced as the aircraft levelled out at an altitude restriction during departure, and proceeded to "bounce" up and down as the thrust changed. It felt very unnatural, and ultimately I stopped flying the 747 because the 777 made a much better job of it in those situations.

Exactly my sentiments .. the generalized criticism for almost everything they do for the most part is annoying and i don't take part but as it regards to this issue of taking "bites" out of what should be a smooth arc is my pet peeve as well. If they fix that + the ground handling +  smoothing out the spool up when exiting the noise abatement procedure i would be pretty much happy.

[jon b]

19 hours ago, ahsmatt7 said:

I wonder if it’s an airline SOP thing but at my company, hand flying any RF leg is prohibited. 

 

18 hours ago, Stearmandriver said:

Really?  Oh yeah, that's a company thing.  We do it all the time, down to RNP .10.

Maybe it’s type specific as I remember on the 744 it was a requirement to use the autopilot, the reason being there wasn’t a high enough resolution on the flight director.

[somiller]

21 minutes ago, jon b said:

 

Maybe it’s type specific as I remember on the 744 it was a requirement to use the autopilot, the reason being there wasn’t a high enough resolution on the flight director.

I thought the flight director is what "directs" the autopilot...no flight director, no autopilot.

[polosim]

1 hour ago, Stearmandriver said:

But it's really odd how completely unable they are to admit that at PMDG.  They seem pathologically unable to admit they've made a mistake, or that something isn't perfect but as good as they can make it. 

Now PMDG begins to sound and give the same poor excuses that Aerosoft gave us.... Oops, wait a minute... 🙂

[Bobsk8]

11 minutes ago, somiller said:

I thought the flight director is what "directs" the autopilot...no flight director, no autopilot.

He said the resolution on the flight director wasn't enough, not that it was missing altogether. 

 

[ianb2469]

Following this with interest. I’ve held off buying iFly for the obvious reasons of it not being fully done etc, but would be curious on opinion as to how that handles RNP legs etc. I agree the left and right twitching is irritating and makes the aircraft appear to be far lighter than it is. I don’t see that behaviour in the Fenix for example. 
 

I also agree that I don’t love the generic PMDG bashing but equally where there is evidence of an actual issue that is being ignored, then I’m comfortable to be involved! 

[threexgreen]

They said the 737 will receive the same improvements from the 777, so I'm not surprised the 737 has the same issues that the 777 still has in this regard. Talking about LNAV improvements for, like, 10 years and then still not nailing it is a letdown.

Though I still stand by what I said after the 777 release. It's better than it was before. It's not where it could (and probably should) be, but the F/D in the 777 is at least easier to follow now and it doesn't wobble as much as the 737 used to, even though it still does. They are coming closer but aren't nailing the touch down.

What I always found odd though is that the wobbling in the 737 started after they pushed an update for it at some point. It didn't wobble before that update.

[ATRguy]

1 hour ago, ianb2469 said:

Following this with interest. I’ve held off buying iFly for the obvious reasons of it not being fully done etc, but would be curious on opinion as to how that handles RNP legs etc. I agree the left and right twitching is irritating and makes the aircraft appear to be far lighter than it is. I don’t see that behaviour in the Fenix for example. 
 

I also agree that I don’t love the generic PMDG bashing but equally where there is evidence of an actual issue that is being ignored, then I’m comfortable to be involved! 

It does them quite well, and yes it goes back and forth a bit in LNAV; I'm hoping the pending update sorts that out a bit.   I've been enjoying the MAX more than I thought I would, probably because my airline will never get them haha.  Heck, we just got NGs to replace our CLs!

[ianb2469]

49 minutes ago, ATRguy said:

It does them quite well, and yes it goes back and forth a bit in LNAV; I'm hoping the pending update sorts that out a bit.   I've been enjoying the MAX more than I thought I would, probably because my airline will never get them haha.  Heck, we just got NGs to replace our CLs!

Thanks. I’ll standby then. And I know we get 737 weary but I’d love a -300/400 to complete the set! Wishful thinking I think.