Dear All,

My last two flights in MSFS2020 with the iFly Boeing 737-8 have resulted in the aircraft going out of control.

The take-offs have been fine and I then engage the autopilot with VNAV and LNAV set.

The aircraft then climbs normally and the aircraft follows the flight plan correctly.

Then, after roughly 5 minutes, instead of going to the next waypoint, the aircraft starts turning to the right and the turn tightens resulting ultimately in an almost out of control spin.

On the first occasion, I managed to regain control, reset the autopilot and the aircraft climbs normally.  However, after reconnecting the LNAV, the aircraft starts turning to the right again, at which point, I give up and close the flight.

I then tried the same flight with the PMDG Boeing 737-800 and completed the flight without any issues (as expected).

May I ask if anyone has an idea why the aircraft has these issues?

Just one other point - I recently upgraded my PC and before that, the aircraft was fine.

Best regards,

Peter

 

Considering the slow rollover happens repeatedly in the same direction, it seems likely that inputs from your controller are overriding or interfering with the auto flight.  There are a few ways this can happen.

  The very first thing I'd check is your controller lockout settings in the EFB - make sure they're turned on.  

Then, there's the possibility you're ending up in control wheel steering (CWS) roll mode for some reason.  This can be caused by you selecting it, or by the aircraft reaching a disco or other problem with your route in the FMC and reverting to CWS.  To diagnose this possibility, we'd need to see screenshots of your FMC legs page, and the flight mode annunciator (FMA) - this is the top part of your PFD where armed and active modes are annunciated.  Looking at the buttons that are vs aren't lit up on the MCP isn't helpful for this, you've gotta reference the FMA.

Speaking generally, the iFly's handling of LNAV is very good, the best I've seen in a 737 in a desktop sim and I've tried them all.  I guess the last possibility would be an issue with how this specific procedure was translated into the iFly navdata by navigraph, but I'd consider this the least likely option.

In my case....after extensive troubleshooting (i.e. pulling the remaining 3 hairs out of my skull), I realized that I had a button on my Bravo throttle set to the rudder trim and it randomly spiked and pushed the rudder into a hard-over, causing the issue you describe.

Check your rudder trim indicator the next time it happens... if you've already checked for and cleared random rudder trim assignments on all of your hardware controllers.  If it happens again, or if you see the needle jittering....that could be your issue.

To add to @Stearmandriver 's info about locking out your controls when the AP is engaged....Here is where you find that page on the EFB...and where the info is in the excellent iFly manuals. 

 

Edited September 19, 2025Sep 19 by Steve Dra
additional info

Trim runaway... Good thinking!

This plane does have some bugs that are kinda annoying, nothing game breaking, just inconvenient. The WPT/ALT in the VNAV DES page doesn't work. Also, if you have a STAR that ends in a (VECTOR), it doesn't autosequence the final course. When intercepting an LNAV course, it doesn't engage LNAV (draw a line from ppos to the course), just arms it. VNAV will blow right through 250/10,000 on descent without leveling off. Haven't tried seeing if VNAV ALT past a T/D will cause the speed bug to decrease or not yet. Haven't flown a MAX, so these may be plane specific. The flight director seems off as well...very slow to anticipate/react when hand flying. 

Still nice to have a 73 in 2024 though. It is still a joy to fly. 

The wpt/alt in the descent page definitely does work, it just doesn't accept a manual entry.  Also, I'm not sure what you're looking for it to do on a vector leg?  Vector legs are forever... They don't auto sequence anywhere?

Also, VNAV definitely honors 250 at 10k, assuming you've got it in the box properly.  Thankfully, you can disable VNAV ALT since most operators don't use it... But yes, if hung high, it'll commands a decel.  I believe it's U12.0 in their FMC.

Edited September 20, 2025Sep 20 by Stearmandriver

Dear All,

Thank you for your replies.

As I mentioned earlier, prior to this issue, I was able to successfully complete my flights with the MAX.

I also fly a variety of other airliners and I have no issues with them.

I'll do some more checking on my next Max flight and I'll let you know how I get on.

The thing that I'm struggling to understand is why the aircraft follows the route perfectly and then without me doing anything, it doesn't go to the next waypoint.

Just to also say that there were no discontinuities in the route.

Best regards,

Peter

9 hours ago, Peterwk said:

The thing that I'm struggling to understand is why the aircraft follows the route perfectly and then without me doing anything, it doesn't go to the next waypoint.

Grab some screenshots of your FMC and the flight mode annunciator next time it happens and we'll be able to sort it out.  This isn't an aircraft bug 😉.

I will do this. Thanks for your offer to help. 

Dear All,

I just completed a flight with the iFly 737-8 MAX and there were no issues.

The flight was excellent and I was impressed with the VNAV operation.

The only thing that I changed was to update the navigation data.

Best regards,

Peter