MCP speed setting problems (733 v1.2)

[slgoldberg]

Hi, folks.

Before I post a detailed bug report (probably two separate ones), I would like to just reconfirm whether these are known issues or really obvious problems, since I scoured this forum and the web in general, but could not find mention of these anywhere. (I also looked in the documentation that came with the plane, but no joy.)

First, I have to say this is a really great and realistic implementation of the 737-300 -- great job!

I believe you have said that the VNAV implementation is still not 100% robust, so I assume the first problem below is just a symptom of that. But if you haven't seen this, it would be good to make sure:

(1) VNAV mode descents, FMC speed versus pilot/MCP speed authority.

This really causes VNAV mode to be unusable for descents for me. I watched the very awesome tutorial video several times to be sure I wasn't doing something wrong, but I can't even replicate that functionality; the problem happens in that case for me as well:

There does not appear to be a "speed intervention" control like on later versions of the 737, so I assume I can't actually use VNAV at all when the FMS speed is not what I want. But I am not sure if there are cases where I can actually set the speed myself on the MCP while still in VNAV mode. But either way, the problem is in VNAV mode.

When flying a flight plan with sensible (and valid) altitudes for every waypoint (best example is no STAR, just the KSFO 28L ARCHI arrival which has altitude restrictions along the path that are all very sensible, all in a straight line, etc.) in VNAV mode, I see the little green circle on the map that shows when it would normally reduce speed. In addition, I've filled out the correct flaps setting and speed reference on the approach page of the FMC, so it supposedly knows what speed I need to be at for each flaps setting, etc.

For the problems I'm seeing, I also make sure I'm already past the "T/D" icon and that the DES page is automatically selected on my FO side, so it is in descent mode and it is honoring the changed altitude I've set in the MCP.  So as it's descending, and it passes the green circle, it's not behaving as it does in your videos.  Despite having the approach reference settings for flaps, I never see that speed in the DES page that you show with the "/FLAPS" tag or whatever it is.  I have seen it sometimes, but not in this case when I really need it.  In fact, I believe (I need to do a full test to get his all nailed down so you have the facts), I have mostly only seen it stay at 250 knots sometimes faster, on the descent through T/D. It never seems to slow to 230 (or if it does, it still has the following problem).

Through several attempted methods, I think I finally get it to set the speed correctly and I get to 230 knots, so I can put down flaps 1.  And I thought it was the case that, in VNAV mode, once you're at 230 or below, you can invoke flaps and it will correctly set the FMS speed to be according to the flaps speed schedule (as in your tutorial video).

However, at this point, flaps 1 starts a chain of frustration and potentially deadly consequences (if this were the real world :-) ), that makes me have to abandon VNAV mode right when I really want it the most...

As soon as I hit flaps 1 (with speed at 230, and FMS in descent mode with descent page configured for flaps 40 reference speed, normal winds just a few knots of headwind), the MCP speed indicator lights up (normally it's blank in VNAV mode). It shows the current speed with a "B" indicator to the left of it (though it's been hard to find, and I'm not a real pilot :-), I can't find what the B actually means, but I believe from experience it means overspeed for the flaps?), but it *doesn't* lower the speed to the official flaps 1 speed, and it doesn't reflect any change in the DES page in the FMC, so I'm very very confused. Why am I not seeing what you see in your tutorial flight? When and how am I supposed to take advantage of the "/FLAPS" automatic settting of the speed in the FMS? Is this a known issue or something I'm doing wrong?

In this case, unless I kill VNAV mode (and even then I don't know if it will let me change the speed yet), and no matter what I do, I can't take over and change the speed. I try to move the speed knob and I see it lower a little but then it immediately pops back up to the top number that I don't want, and then I am forced to either flaps-up again or disconnect VNAV mode.

To be very clear, I'm not at all stalling nor anywhere near stall speed. So this isn't alpha protection (which I believe is an A, not a B, anyway, right?). I am going quite fast, descending, trying to slow my descent so I can acquire the glideslope for an ILS landing etc. I do all that just fine, but it's very frustrating with the flaps and speed. I know the logic is inverted in VNAV mode, since normally you set the speed you want when you aren't using VNAV, and you either do a speed-limited descent or a rate-limited descent. And when I do those, they work fine. Except for the bug in (2) below, but .. I am always able to land successfully using ILS. It's just really frustrating that the handoff from descent mode after passing top of descent to autoland mode with G/S and both APs engaged, is a real battle while VNAV is engaged, whereas normally it would be quite elegant.

(2) MCP speed knob "stickiness".

This is a big, actually really big problem for me and I'm wondering if it's also a problem for others.  I'm happy to spend some time troubleshooting and trying different test cases to see what causes it to fail, but right now it's really very random (maybe 1 in 15 times I turn the IAS knob in the MCP, regardless of which mode I'm in).  In fact, it happens on other dials, as well, but this is the on that really destroys me:

Every once in a while (about once every 15 times I use the IAS knob using my mouse cursor on Windows 10, XP11.05), after I've finished setting the speed I want and released my finger from the mouse button, I discover that in fact that speed dial did *not* release from my cursor, and though I'm moving my cursor off to another control, it's actually inadvertently continuing to change the speed setting in the MCP!  This is really brutal! There have been times on descent, where I am at flaps 10 and I just want to lower the speed to landing speed, so I dial it down from 190 to let's say 129 knots for example, and after ten seconds of me moving my mouse around getting ready to maybe click another thing with my mouse, I suddenly realize my speed setting has been tracking my mouse unbeknownst to me! And the speed is now set at 250, sometimes higher!  Of course, by the time I realize the error, I'm usually very close to if not already over speed for the current flaps. It's horrible. I am really frustrated by how difficult it is to fine-tune the speed anyway, but it's even worse when sometimes the mouse doesn't actually "let go" of the speed dial!  I can easily replicate this, but I can't give a simple test case that will guarantee that it happens, I just have to keep using the knob and for certain it will "stick" at some point in the next 10-20 attempts.

Has anyone else reported or seen this perhaps?  Not just with the speed, but certainly that's the worst case. I have a lot of different planes, and have never seen this with any of them. This is really the first time this has ever happened to me (and I bought this plane only starting with v1.2, so I don't know if it predates this version or not).

Thanks!!

  Steve

 

[Litjan]

Hi Steve,

thanks for the nice words. I skipped (well, skimmed over) your paragraph on VNAV, the green circles, and altitude restrictions because it is not really implemented yet and doesn´t work like it should in the real plane. Please resort to basic airmanship when planning your descents and use basic autopilot modes for now. This is actually the way the 737 is flown in most cases. Improving VNAV is on our agenda.

VNAV will not honour the flap placard (maximum) speed during the descent - it will only honour the "lowest maneuvering speed". So if you are in a segment where VNAV wants to fly 250 and you extend your flaps, bad things happen. But if you are in a segment where VNAV wants to fly 160kts and you don´t extend your flaps, you should see the 210/FLAPS and the plane will not slow down below that. Again, this may not always work right now.

It works the other way during climb. VNAV will always fly either its desired speed, or current flap setting placard speed -5, this works pretty well, already.

The "B" you are talking about is actually a "all segments lit" and signifies a placard speed reversion. The autothrust kicks in and reduces power to stay at 230kts exactly. It will not try to fly a "safe" speed, it is just a pretty crude reversion mode to avoid ripping off the flaps. 230 is the absolute maximum to fly with flaps 1, it is better to extend flaps to 1 when you are well away from this placard speed. I recommend 225 for very heavy weights (>53.000kgs) or 215 when below that.

You are right, you need to exit VNAV to exit the speed reversion mode, so just click FL CHG, dial the MCP SPD down by 15kts to get out, then click VNAV again (if you rely on using it during the descent).

I am not covering these mechanisms in my tutorials, because they are way over the head of most users and would just confuse people. In 10 years of flying the real 737 I never triggered a speed reversion, that is the goal, here. Wait until speed diminishes and you are safely below the placard speed - and watch for VNAV misbehaving, with the imperfect implementation we have it COULD accelerate again after passing a certain waypoint.

On the manipulators sticking: You need to have the manipulator on your screen (iirc) to release it - if you grab it, then look away, you can´t release it. The mouse-view works the same way, if you move the cursor off the screen, it "sticks". I agree this is not ideal, but I think it´s an X-Plane limitation.

Hope this helps, Jan

 

[slgoldberg]

Thanks, Jan -- very useful, in the sense that I wasn't too sure of how much I should expect from VNAV mode on the descent and it sounds like the answer is clear: not much. :-) So, okay, thanks.  BTW, I also couldn't find a "DES NOW" button on the FMC and I assume that's something you removed after your demo since I believe your tutorial video actually did show it at one point (though you weren't using it; I thought I saw it there on the descent mode page).

Either way, if I am not using VNAV for descents, then I guess I don't need DES NOW.  But it would be nice to be able to start a descent a little early in certain cases... but I digress. :-)

Re: the manipulators sticking -- no, I'm absolutely not looking away when this happens. I know what you mean, but that's not it! I've had that happen in other places when looking away, and agreed, that's not something people should expect to work correctly. However, in this case I'm not looking away.

The most common issue for me comes if I have to frequently adjust my speed when otherwise "stable" during final). I.e., to keep it in the window as the headwinds might be changing radically over the 5 minute period that matters most. To keep the plane stable in that last phase (normally in ILS autoland mode, i.e. with both sides in command mode), I will dial the speed up and down just a few knots, using that speed knob (clicking, dragging, and letting go for each change).

Though in fact, the mouse cursor control over the dials such as MCP SPD and HDG is a little frustrating at times. Sometimes it will not let me switch directions (I will switch directions and see the dial spinning the other way, but the numbers will continue to go in the direction I had been going earlier, i.e. speeds may only decrease until I let go and re-click and start a new drag to go the other way -- but that's intermittent as well).  But either way, just moving the dial 1-2 knots (for speed for example), can be a little difficult. I often find myself having to make several adjustments before it ends up where I want it.  So, this sticking problem just really exacerbates that usability issue, considerably, when it happens. :-(

I guess I need to either write a little plugin to just let me have a screen location to adjust the MCP SPD by +/- 1 knot, for those cases -- or else, presumably I can just map that to a separate hardware control or to keys on my keyboard. Because grabbing that dial with the mouse cursor as it is is already pretty risky (things might move much more than I want them to).. But it becomes 10x more risky when the button might stick especially if I forget about it and go on after thinking I've made the adjustment, to then move the mouse unwittingly changing the speed much more radically.

Ideas welcome on that -- but it sounds like nobody else has complained of this and you're not seeing it; so I wonder if it could be specific to my mouse (even though I don't see it on any other planes). I definitely see it on many controls within this particular plane, though; I had it happen today on the heading selector (also in the MCP) and while that was easier to notice since the map would also show the heading graphically, it was still a little irksome. :-)  Anyway, I'll just try to figure out a way to avoid it for now. I just didn't expect to be the only one to see this problem.

And just to be clear re: the first issue with the VNAV descent speed and flap speeds, etc. -- of course, I can readily switch to using the more traditional FL CHG or vertical speed mode, but those of course as you know require more skill than I'm necessarily equipped for today (including having to actually plan my descents whereas in VNAV mode I can focus more on other things). But it's all good.  I suppose I should really take this opportunity to practice non-VNAV descents since your plane is much more realistic in most other ways for those.

Thanks again.

  Steve

[admroz]

8 hours ago, slgoldberg said:

I guess I need to either write a little plugin to just let me have a screen location to adjust the MCP SPD by +/- 1 knot, for those cases -- or else, presumably I can just map that to a separate hardware control or to keys on my keyboard. 

I think that mapping keyboard for these dials is the best solution. I have mapped F1/F2 for SPD (sim/autopilot/airspeed_down / *_up), F3/F4 for HDG and F5/F6 for ALT. Works perfect for accurate adjustments and since it uses sim/autopilot/* commands it works with other aircraft too.

[Litjan]

Hi Steve,

just some quick thoughts - everything that VNAV does can also be done with the basic modes. Instead of clicking "DES NOW" you can select V/S -1000 and experience the exact same thing. VNAV is a bit more comfortable in theory, but in reality you will rarely fly an approach in the real world as programmed in the FMS, and with every shortcut or extension your predetermined VNAV descent path will crumble and you are left to improvise.

Don´t change your approach speed around. The autothrottle is certified to compensate for gusts, so you will always only ever set Vref+5 and just leave it there, no matter the wind. Only when flying manually you would set a higher target speed - but it is never changed during the approach, unless the tower reports a radically different wind.

I am personally not convinced that the (real) autothrottle is so great at compensating for gusts, so I would maybe add another 5 in really windy conditions just to stay away from that stick-shaker experience...

The "sticky" mouse could be due to your system performing some taxing background tasks that saturates the CPU and causes certain mousepresses or releases to not register. Maybe try to run X-Plane as clean as possible to troubleshoot - especially removing all plugins not needed, just to see if it helps.

The problem of "reversering" the direction is known and appearantly very hard to solve, I have made it a habit to always "grab again" when I change direction. I agree that the MCP ALT button is too sensitive, I have been pestering Nils to tune it down...to little effect, so far :-)  But I haven´t given up hope! There is also the element of "familiarity", I guess if you moved those buttons for 7+ years like me, you adapt...

And yeah, I invite you to plan your descents - it is actually quite satisfying when it works out and it is also required when flying VNAV - even the real system is absolutely not failsafe and you need to know when to step in and show the computer who is the pilot ;-)

Cheers, Jan

 

 

 

[slgoldberg]

1 hour ago, admroz said:

I think that mapping keyboard for these dials is the best solution. I have mapped F1/F2 for SPD (sim/autopilot/airspeed_down / *_up), F3/F4 for HDG and F5/F6 for ALT. Works perfect for accurate adjustments and since it uses sim/autopilot/* commands it works with other aircraft too.

Great idea, thank you!

 

44 minutes ago, Litjan said:

Don´t change your approach speed around. The autothrottle is certified to compensate for gusts, so you will always only ever set Vref+5 and just leave it there, no matter the wind. Only when flying manually you would set a higher target speed - but it is never changed during the approach, unless the tower reports a radically different wind.

Wow, this is mind-blowing. I don't know how I never understood that about approach speeds. I wonder, do you think that's true for most/all of the planes I might be flying that also have autoland features? For example, I often do this speed varying stuff on landing in the x737, Rotate MD-80, FF Boeing 757, etc., etc.  Are you saying I should not be doing that? It seems I have to, in those planes, because they seem to all have a really rough time maintaining stable approach with just Vref+5 as the speed setting in the MCP.  They all make me set the speed myself at the end (not sure exactly when) and if I don't change it from whatever's there by default (usually Vref+5) after handoff from VNAV mode during the final phase of landing, I feel the plane might drop out of the sky.

For example, with 15 knot headwind, in most planes at least, if I don't manually set the speed to Vref+5+15 (to account for the headwind), the nose goes too high and the longer I wait to add airspeed, the further below the glideslope I end up, which doesn't seem right of course. :-)  If this is the only plane to do it "right" and it's not something pilots really have to do, then that's great to know and I'll happily stop doing it because it's quite stressful monitoring the headwind constantly (though I modified a plugin to make it much easier so I can always tell the exact headwind component -- or tailwind if it is the case -- of the current wind hitting the aircraft). But yeah, I guess that wouldn't be how real pilots do it since they don't have the plugin. :-)

Regardless, that's really good to know that it should work that way.

Quote

The "sticky" mouse could be due to your system performing some taxing background tasks that saturates the CPU and causes certain mousepresses or releases to not register. Maybe try to run X-Plane as clean as possible to troubleshoot - especially removing all plugins not needed, just to see if it helps.

Yes, I am sure when I have time I'll try that. However, I'm almost positive it's not the case here. My very naive sense is that maybe this plane (blame Nils, I hear?) does custom handling of these basic gesture inputs, and I really wouldn't be surprised if there is a timing bug that only happens to show up in my configuration, or it's more common but most people just don't care or don't use the mouse as much as I do. Note that with the x737, I've used a touchscreen running AIr Manager where I can have a touch-based MCP that allows me to just put my finger on the outside of a dial and spin it either direction to control it. It works great, so maybe I'll either try that with this plane, or hack together something. :-) Not a huge issue, obviously, I was just curious -- since thankfully you do use standard datarefs for the basics which I can't say about everyone else. :-)

Finally, just in case it helps you in your VNAV implementation, I wanted to share a very brief video showing one example of how VNAV mode on descents can be extremely difficult to deal with. In this case, I was flying a flight plan with cruise altitude below FL100 (which may be a problem in and of itself; I think these bugs don't show up in higher cruise altitude configurations). Just before passing T/D (in VNAV mode, cruising at FL080 and speed at 250 KIAS), all is good; then I pass T/D and I enter descent mode. Surprisingly, the speed limit bug on the airspeed indicator moves up to 270 knots, instead of going down to 240 or 230 which would be expected (or at least staying where it was since it is below FL100 and thus should not be above 250 anyway). That was confusing enough, but then I did something I probably shouldn't do and edited my FMS route to show speed 230 on my next waypoint. However, immediately after hitting that waypoint (I think), the speed bug rocketed up to *over 400 knots*!! Remember, at this point I was only at FL060-FL070. It was not appropriate under any circumstances to go that fast.  Anyway, the video starts right then. I just wanted to show a little bit of the troubleshooting and how frustrating it was :-) and that's that. I don't need to go further on it, I know it's not working, but just in case it helps you think about what might be mucked up. :-)

Thanks heaps.

  Steve

 

[slgoldberg]

Update: I think the VNAV is actually working relatively well on descent under "normal" conditions. What breaks it horribly is when your cruise altitude is less than (or probably equal to) FL100.  This is why every time I do a circuit to test this stuff, I run into this problem -- but I don't have it really at all when I'm flying VNAV mode descents from higher (typical) cruise flight levels.

For most circuits, I just do the minimum flight level I can fly at with a relatively short flight path around the airport. So normally for a circuit I'll end up with something between FL040 and FL080. Anything higher is usually too hard to achieve unless I add waypoints further away (or fly a STAR with a farther-away transition). So that's why I wasn't really seeing this with some of my longer flights (which I forgot to mention earlier).  For longer flights with cruise altitude from FL110 and above, I have only seen it do "normal" things like cut out VNAV once I go to flaps 1, or if I force it to re-engage VNAV mode, and things work great up until a point, maybe I'll have a minor nuisance where it didn't plan the vertical path very well and thus didn't do any better than I could've done with v/s as we agree. :-)

So anyway, I just thought I'd throw that extra information in there in case it helps with the development of the full VNAV functionality at some point.  If you can't reproduce the problems I'm seeing by simply lowering your cruise altitude to FL080 or so, let me know and maybe I can provide more useful data.  To be clear, the problems I'm referring to with flights under FL100 are for example what I show in the linked video above (crazy high speeds in excess of 400 knots when at FL060 and normally the speed should be 230!). I'm hoping we can all agree that 470 knots is never appropriate under FL100. :-) Nor even above since by then it should be in Mach. :-)

Thanks again. Hope this is helpful, let me know if I can provide any troubleshooting data but know that I may not have time to really do much because of my "real" job. :-) But happy to at least try to get some basic examples if needed. (Beyond what I uploaded above and what's written here. :-) ) Thanks yet again...

  Steve

[PilotNL]

The way I was taught to fly the classics was with a fixed set of speeds for average weight. Clean/210 Flap1/190 Flap5/170 Flap15/gear-down/150 Flap25/Vref+5. For heavy weights add 10 knots to all speeds. Set flaps 10kts above previous flap speed, for example from 250kts: set speed 190, when passing 220 set flap 1. Hope this helps!

Sent from my iPhone using Tapatalk

[IronCondor]

Interesting thread. New IEXG 737 owner. I understand that the VNAV is not fully implemented for descent. I have noticed it works well above FL100 as well. Jan, when you stated use basic airmanship, how is the descent flown in the real world? LVL Change? VS at -1000? I am curious to know? I have managed several manual descents very well. I have changed MCP SPD to many rate of descent in LVL Change. 

 

Abe

Edited August 22, 2017 by IronCondor

[Tom Stian]

9 hours ago, IronCondor said:

Interesting thread. New IEXG 737 owner. I understand that the VNAV is not fully implemented for descent. I have noticed it works well above FL100 as well. Jan, when you stated use basic airmanship, how is the descent flown in the real world? LVL Change? VS at -1000? I am curious to know? I have managed several manual descents very well. I have changed MCP SPD to many rate of descent in LVL Change. 

Abe

Im no pilot, so I can't give you the answer how they are using it in the real world.

But in this video you can see they are using v/s pretty "heavily".

 

I simply use the mode that are solving what I try to achieve.

So for max descend I often use LVL CHG.

For a more controlled descend I use V/S. So if ATC says; cross "waypoint" at FL140, you can easily do that with V/S.

And I often use V/S to slow down to 240kts before I go below FL100. Which gives a more smooth ride