There are indeed - Always, Never and Hold Only. There are posts in this thread, on the PMDG forums and the Discord discussing the plusses and minuses of each mode.
Yes, thanks! For testing right now, I have it on Never.
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Hoping someone can help. Iām doing one of my first āproperā flights in the PMDG 737-800, and at cruise over the ocean, there are these moments where it seems to freeze for about 5 or more seconds. The computer doesnāt freeze, and in fact, I can still pan the camera, the mouse moves, and the co-pilot is still animated, glancing around - itās as if the PMDG plane has paused. Itās very odd.
I know when it happens because the sound changes slightly (a kind of deep rumbling, Iām using the ānoise cancelling headphonesā that you click in the virtual cockpit to reduce cockpit noise), the clouds out the window stop moving, and the Chrono freezes. If I try to click, nothing happens until it unfreezes. But I can switch to external view, and back to cockpit, and it immediately just continues flight normally.
I turned on the MSFS FPS overlay to see if it showed any issues, but it just continues to run normally, and it gives no indication of a problem (all green). I can wait it out, and it recovers, or I can switch to external view, then back to cockpit, and it recovers.
Iām on PC, MS Store, SU 4, all streamed, default livery, and the only addons are BATC and the FSLTL models that BATC injects for traffic. There is no traffic around when this happens. 9800X3D, RTX 5090, TAA, Max Frames 31 + FSR3 Frame Gen x2. Temps are all good, everything seems perfectly fine, so I canāt explain it.
Any ideas what this might be? It doesnāt happen in any other aircraft.
That sounds like an autosave going on in the background - are you using Volanta, Elevatex, VA software or anything else that runs alongside the sim that is doing autosaves?
Nope, nothing. Generic install of Windows 11 25H2 about 2 months ago, for the sole purpose of MSFS. Hibernation disabled, along with things like system notifications, etc. Otherwise, just all vanilla.
Itās not the computer freezing, itās the PMDG flight seeming to āpauseā. I can pan the camera, the copilot is animated, moving, I can click to open the cockpit door, etcā¦ If I go to external view, all the sounds are still running, but the plane is āpausedā in the sky, as is the contrail. I can pan and zoom the camera around the plane, inside and out. Nothing else is frozen.
And I donāt have pause at TOD active or anything like thatā¦ No ACARS, Hoppie ID, or CPDLC, only the default PMDG settings. I have not clicked Pause, or Active Pause, and it will happen when Iām just watching the clouds roll past (no active inputs). This is definitely limited to the plane itself. Maybe Iāll do a flight without BATC.
Ah ok will do, good to know 
Having difficulty working out how to control speed.
I was descending in V/S mode and had heading and speed buttons enabled, even after levelling off speed was not reducing.
vnav and lnav were off, auto throttle enabled.
I reduced the speed knob but speed would not reduce.
I have also noticed this and Iām on Xbox series X.
V/S mode gives no speed protection, so whenever your rate exceeds the thrust or kinetic energy of the plane, it will not hold speed. The speed howerver should have reduced to the set speed after loosing inertia, reengaging the thrust levers out of idle. So I am not sure why that did not happen after the level-off.
FLCH and VNAV modes are speed governed and protected. You can change the FLCH rate by changing the speed.
You maybe need to do a bit of theory studying in order to properly understand the modes of your AFCS - it is actually crucial to maintain control of the aircraft.
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Thanks, maybe I should have used the speed brakes as well to help, I should have added the speed did seem to drop after levelling it just seemed to take a while, but again I think speed breaks would have helped.
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Yes that would have helped for sure.
I am not sure if the real 737 behaves exactly like the PMDG though - the latter does seem to lack a very ever so slight bit of drag coefficiant in the flight model in the clean configuration. Of course inertia also depends greatly on your current weight and also an increase in wind component have an affect. (I mostly fly the BBJ version in MSFS so when on descend, the aircraft is mostly very light because of low payload numbers and not too much fuel remaining.)
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Itās a very fine balance to get that right in the sim, but weāll have another look at these drag figures.
Mathijs Kok
PMDG
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Excellent input above about using FLCH or VNAV, and you own observation regarding Speedbrake use. Wondering what else was going on in your flight when descending in these modes? Were you flying you own flight plan or attempting to comply with ATC when the speed management issue arose?
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Was using simbrief flight plan, I normally just let it do its thing by descending when it reaches TOD, but was just wanting to try some manual intervention.
Next time I will try FLCH, as I understand as above that is speed protected and the rate of descent is based on my set speed, where as V/S just descends at any rate I set disregarding set speed.
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Ok if by normally you mean you descend in VNAV following your flight plan, and you want to try something new by way of manual intervention, yes I agree that FLCH would be the next most logical mode to get to know. You will still need Speedbrakes on many 737 descents regardless of which vertical mode you choose, so keep an eye on energy during your descents and do anticipate Speedbrake use to keep the descent within the parameters that the A/P can manage, else you will have even more work on your hands. You have come across some important teachable moments!
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Yeah sorry, normally let it descend in vnav mode, but a few times Iāve noticed issues with my flight plan on approach, so need some manual intervention, buts thatās a different issue.
Although I was quite pleased with myself yesterday as I managed to somehow join up the flight legs in the FMC, no idea how I managed it!
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No need to apologize! This is how we learn and pilots are problem solvers, so kudos to you for managing through!
May I suggest doing a few more flights with VNAV descents and getting more comfortable with Speedbrake use before venturing into the other vertical modes? Hanging around here I have learned that they are a mostly an on/off thing, meaning that they are most effective when fully deployed to the flight detent; also that they are more effective at lower altitudes where the air is more dense. Anyway, good conversations above and good flying ahead!
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I should, I take it with a simbrief plan set up correctly along with vnav and lnav should bring the 737 down without much user input.
I just seemed to remember being a little too fast before on approach in these modes, but I could have used speed breaks.
Thanks everyone.
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Thereās no need to hesitate to use them. Yesterday I was a passenger on KLM 737-800 to Amsterdam and the pilots were using the speed brakes a couple of times for 1-2 minutes. I rarely use them in PMDG 737 but the truth is that I always start a descent on VNAVās calculated TOD.
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Iām going to have to try mapping the speed break to my spare throttle axis on my flightstick. That will make it a lot easier than using my mouse cursor to move it which is fiddly.
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