Differences between the NGX and the current real 737

[Flexman 30]

Hello,

Can we expect PMDG to update some of the AFDS logics in the NGX before a new full release comes out? Particularly I mean the way the real 737 now stays in VNAV PTH always during descent, unless the pilot pushes speed intervent to open the speed window to engage VNAV SPD. In the real 737, if you stay high and then you engage VNAV, AFDS will activate VNAV PATH and the airplane will just dive with no respect for speed. VNAV PATH does not care about speed when trying to get back on path. It's supposed to not exceed MMO or VMO, but it often does and you can easily hear the clacker. The NGX has the old mode in which if you go VNAV when you're really high off the intended descent path as per the speed in the descent page, it will stay in VNAV SPD and it will not dive unless you increase the speed in the now open speed window in the MCP.

Also, I've noticed FMC SPEED bug in the real airplane will not move instantaneously to a new speed (ie a preset restriction) and it will slowly roll back as the airplane decelerates.

Are these things to expect in the coming releases or something that we could see as an update to the current NGX?

[ph-cxz 28]

The chance is pretty high it will be in the ng3 but now words have been said on what it includes.

[scandinavian13 5,192]

16 minutes ago, Flexman said:

Are these things to expect in the coming releases or something that we could see as an update to the current NGX?

Nope. They're not the bugs you're assuming. They're differences in the software versions and options between what we've modeled and your carrier.

[Flexman 30]

Thanks! The 757 I flew behaved like the NGX does but the 737 I fly now has this crazy thing that, unless you intervene speed during a descent, it stays in VNAV PATH even if it's high above path. I prefer the version modelled in the NGX. I'm not sure it's safer towards preventing high energy approaches, but it's just more confortable. It's like: Hey, you're high, here the speed window, now you fix it. I thought it was an old/new thing but I guess it's just an option you can get from Boeing.

[scandinavian13 5,192]

18 hours ago, Flexman said:

Thanks! The 757 I flew behaved like the NGX does but the 737 I fly now has this crazy thing that, unless you intervene speed during a descent, it stays in VNAV PATH even if it's high above path. I prefer the version modelled in the NGX. I'm not sure it's safer towards preventing high energy approaches, but it's just more confortable. It's like: Hey, you're high, here the speed window, now you fix it. I thought it was an old/new thing but I guess it's just an option you can get from Boeing.

Welcome. Yeah, to be honest, I get so lost in what plane, and what software version in that plane, behaves in which way...it's a lot to keep up with.

Interesting to see the discussions between the RW operators that pop up in here, though - both from the perspective that one might fly with the version we model, while another flies a different software version; and from the perspective that someone might have flown with one, and then with the new concept in the new software.

[Flexman 30]

On 12/11/2018 at 2:39 PM, scandinavian13 said:

Welcome. Yeah, to be honest, I get so lost in what plane, and what software version in that plane, behaves in which way...it's a lot to keep up with.

Interesting to see the discussions between the RW operators that pop up in here, though - both from the perspective that one might fly with the version we model, while another flies a different software version; and from the perspective that someone might have flown with one, and then with the new concept in the new software.

Yeah. Well. We have many simulators in my company. Of course the full flight sims are exactly like the real airplane because they follow pretty much the same update schedule, so they all have RAAS and the latest of the latest that you'll also find in the real airplanes. In fact some things appear first in the simulators for testing and training content creation and then they put them in the real airplanes, like the GLS that we're starting to use in some bases. Having said that, we also have quite a few less complex sims that all pilots can book and use for training and some of those have older versions of AFDS and FMS. Some are on U10.8 for the FMS just like the NGX. Our real airplanes have U14.0 with RTE2 and other nice things.

The NGX is just astonishing to be honest. I can use it to prepare exactly how I'll configure the real airplane on some of the approaches. We have airport briefs that tell us the most likely shortcuts we'll get by ATC during terminal operations and being able to prepare those at home as part of my pre-flight preparations is just amazing. When your company wants you to turn the airplane around in 25 minutes, the more you've self-briefed at home, the better.

THE VNAV THING
This is how the NGX does it. You're descending perfectly on path, engines idle, at the perfect FMC SPEED in VNAV PTH and it's all good. But suddenly ATC gives you a shortcut. Now you have less miles to descend so you're suddenly some 2000 ft high. What the NGX does is it reverts to VNAV SPD, which is a fancy level change with FMS level restrictions. The airplane will do an idle VNAV SPD descent at the same speed you were at when all was perfect. The airplane will not catch the path at that speed. In VNAV SPD, the airplane will not dive and it's up to the pilot to increase the speed and maybe use speed brakes to catch up with the descent. Of course we don't do that. What we do is select a higher speed in the CDU to find a speed path that is closer to how high we're left and we fly that and try to get on a faster VNAV PTH instead of the ECON one dictated by cost index... sorry cost index, we tried.

This is how the real plane does it (unless your company doesn't invest in updating these things). You're on path and you're given a vector and now suddenly you're high. The airplane doesn't care about how high you are. It just stays in VNAV PTH. VNAV PTH doesn't care about your speed at all, so it will just dive like there's no tomorrow to get back on path and speed will increase by a lot, hopefully, without exceeding Vmo or Mmo (I said hopefully). When it catches on with the new lower path, you're still in VNAV PATH but you're fast. It's a big threat as you have a lot of excess energy now. It's an important skill for a pilot to know how to overcome this because it's not correct. It's not correct to dive like crazy at a speed you have not commanded, to catch up with a path that was programmed for a slower speed. The correct thing is to select a faster descent path and, only if necessary, use speedbrake to fine tune your speed while entering that new path. The more time you have to correct, the less necessary the speed brakes are.

For you guys to know. The NGX is so good that this little VNAV behavior is the only little thing that I notice is different between the real airplane I fly and the NGX (among the things that are simulated, of course). The other differences are of course because of the lack of full ARINC 424-19 compatibility in the FMS and the poor 3rd party navdata databases that we have to work with. That's not PMDGs fault, but I do hope they find the time to make an FMC that supports all ARINC 424-19. Sometimes I'm in the real airplane and notice how some terminal procedures are just 2 legs in my CDU while in the NGX it takes 5 or 6 points to draw the same magenta line (arcs, procedure turns, etc).

[downscc 1,327]

7 hours ago, Flexman said:

That's not PMDGs fault, but I do hope they find the time to make an FMC that supports all ARINC 424

Slightly tongue-in-cheek, I think they've been planning on updating the FMS code ever since it was first used but the project gets tabled for the 777, P3Dv4 conversions, 747, 747-8, and now GFO and NGX3.... but I think they are thinking about it now.  This is something I've been asking for ever since my first beta test in the MD-11. 

[MarkJHarris 128]

Also I think you mean U12, not U14. U13 is the latest release specifically for the Max. U14 AFAIK isn't out yet. Our aircraft all have U12 on board, but some have Geo Descent and some don't as Options.

[JoeDiamond 67]

On 12/10/2018 at 12:23 PM, Flexman said:

if you stay high and then you engage VNAV, AFDS will activate VNAV PATH and the airplane will just dive with no respect for speed.

What software version?  We have U12.0 and U13.0 and it does not behave like this.  It will revert to VNAV SPD if you are above the path.

 

On 12/10/2018 at 12:23 PM, Flexman said:

Also, I've noticed FMC SPEED bug in the real airplane will not move instantaneously to a new speed (ie a preset restriction) and it will slowly roll back as the airplane decelerates.

The bug will change instantly if it's in geo path mode.  If it's an idle descent leg with the A/T in ARM the bug will roll back slowly.  Again with U12.0 or U13.0.

[Flexman 30]

On 12/16/2018 at 9:43 PM, MarkJHarris said:

Also I think you mean U12, not U14. U13 is the latest release specifically for the Max. U14 AFAIK isn't out yet. Our aircraft all have U12 on board, but some have Geo Descent and some don't as Options.

My bad. I can confirm our airplanes are on U13.0. U13 came out in April 2017. Just checked my FCOM and it says that some older ones are still on 10.8A which is strange because I flew EI-DAD a few days ago and I remember it having RTE2 and all, so maybe, it being the oldest airplane in our fleet AFAIK, I'd assume they've all been updated to U13.0. I also know U14.0 is coming with the MAX and will probably be retrofitted in the whole fleet because we already have FCOM bulletins talking about the "bugs" that we can expect to be corrected in U14.0

Edited December 22, 2018 by Flexman

[Flexman 30]

On 12/17/2018 at 10:07 PM, JoeDiamond said:

What software version?  We have U12.0 and U13.0 and it does not behave like this.  It will revert to VNAV SPD if you are above the path.

That's exactly how the old 757 I used to fly did it. If you're high, it'd go VNAV SPD and if I remember correctly, it'll open the speed window on the MCP for you to increase speed to catch up. In fact that's one of the hardest parts I found when learning to manage our version of the 737. The fact that VNAV PTH has such a large tolerance when above the path, that the airplane will not think twice before diving. People tell me it will happily exceed MMO/VMO... haven't tried in the real airplane. In the sim, with steady winds, it didn't hit barber pole.

 

 

On 12/17/2018 at 10:07 PM, JoeDiamond said:

The bug will change instantly if it's in geo path mode.  If it's an idle descent leg with the A/T in ARM the bug will roll back slowly.  Again with U12.0 or U13.0

Most people I fly with don't question it because, in this company, most people have only flown for this company, so they don't have a comparison point (flight sim or other boeing airplanes). It was very strange for me to see on a 250kt descent, the bug slowly crawling to 220 after a decel point. My initial interpretaion was that the airplane was so bad at keeping that speed in a poorly calculated idle VNAV PTH, that FMS was just giving up and matching the actual speed of the airplane. Now I know what the airplane is doing but since the speed window is closed, I've had to train myself to look at the descent page to know what final speed it's going for, and whether it'll be able to reach it or if it'll require flaps. I don't really like that feature to be honest. In the 757, the bug would just jump instantly from 250 to 220 or whatever speed you had set up in the next waypoint or restriction. No need to look at the CDU.

Edited December 22, 2018 by Flexman

[Attilio 4]

On 12/22/2018 at 4:19 PM, Flexman said:

My bad. I can confirm our airplanes are on U13.0. U13 came out in April 2017. Just checked my FCOM and it says that some older ones are still on 10.8A which is strange because I flew EI-DAD a few days ago and I remember it having RTE2 and all, so maybe, it being the oldest airplane in our fleet AFAIK, I'd assume they've all been updated to U13.0. I also know U14.0 is coming with the MAX and will probably be retrofitted in the whole fleet because we already have FCOM bulletins talking about the "bugs" that we can expect to be corrected in U14.0

Is the older EI-DAC no longer? Is the lease finished?

[Flexman 30]

On 5/6/2019 at 7:29 PM, Attilio said:

Is the older EI-DAC no longer? Is the lease finished?

Oh yeah true. EI-DAC is still around. It's been based in OPO lately.

[MarkJHarris 128]

Have you noticed that when the bug slowly winds back to UP speed and you select Flap 1, it jumps instantly to F1 position, without opening up the window? (And the word not allowed autothrottle wakes up and adds thrust for a second before retarding. Always cracks me up that).

My company is also full of Magenta following JonnyCabs, who no nothing different. It's a shame but while these large European carriers insist on training cadets directly, leaving turboprop crews to rot, it won't change. There's an awful lot of good crews out there, but trust me, Sully-quality is rare.

I'm just glad I came to the 737 after 15 years of flying regional aircraft. Did me no harm at all, though some in the training dept see me as a threat to maintaining standards.. just because of my previous experience! Tail wagging the dog and all that. Can't wait to retire only 15 years to go!