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Popcorn

Possible AP bug or pilot error

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So I'm not sure this is a bug or an error on my end, but the following occurs on every flight with the IXEG 737 classic. Before I describe, I'm using the newest version of X-Plane 11 (11.11) and the most recent IXEG 737 (1.21).

I've input everything possible into the FMC using data from Simbrief. I arm the captain side FD followed by the first officer side so the captain FD is the master. I set IAS/MACH to V2 and set the heading to the departure runway. During taxi, I arm auto throttle. After lining up on the active, set throttles to 40% N1 and then  engage TOGA. VR rotate, positive rate gear up following the FD. "THR HLD" switches to "ARM" and then to "N1" as it should. Usually around 400' to 1500' AGL I engage on CMD A, but every time I do this the A/P P/RST warning light illuminates and the warning sound is heard until I cancel the warning. Even though this happens, the AP is active and working. However, with the AP turned on and "MCP speed" displayed, the plane will pitch down if I let go of the yoke and not hold V2+15. Also, when I increase the IAS/MACH to something higher than V2 + 15, the plane doesn't respond as it should to accelerate. Once VNAV is engaged the plane follows the FMC speed as it should and adjusts the throttle and pitch as it should.

With that said, am I doing something wrong or is this a bug? If I am doing something wrong, can someone please let me know what and how to correct it?

Many thanks,

Chad

Edited by Popcorn

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Hi Chad,

as a first measure, increase your "Autopilot CWS deadband" in the preferences menu, please. I think that your joystick isn´t centered properly or "spiking" and this will kick the autopilot out of CMD.

Cheers, Jan

 

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43 minutes ago, Litjan said:

Hi Chad,

as a first measure, increase your "Autopilot CWS deadband" in the preferences menu, please. I think that your joystick isn´t centered properly or "spiking" and this will kick the autopilot out of CMD.

Cheers, Jan

 

Thank you for the response Jan. I'm guessing that my process is correct since you didn't mention any pilot error. I took your advice and increased the joystick CWS deadband in preferences to the full limit of .25%. Pretty much the same thing happened upon a test departure. After TOGO and engaging CMD A, the A/P P/RST warning still came on, but the good thing is that the AP held V2 +15 once I let go of the joystick and when commanded a higher speed to 210 it worked. I changed it again to 250, and while it increased, it never hit 250 until VNAV was engaged. In both situations, it seemed the auto throttle made adjustments, but the plane never pitched down to achieve the desired MCP speed.

In addition, I also re-calibrated my joystick prior to the test flight to be sure there wasn't a problem with the calibration. If you have any further suggestions, please let me know.

Best Regards,

Chad

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can you share a few screenshots of the forward cockpit to see what the systems and mcp status are?

or maybe a video of the behaviour?

 

thanks

  • Upvote 1

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2 hours ago, mmerelles said:

can you share a few screenshots of the forward cockpit to see what the systems and mcp status are?

or maybe a video of the behaviour?

 

thanks

That is a good suggestion. I just capped a video, but this time everything went well. I checked my CWS settings and for some reason, it was only set to .20, after changing it again to .25 everything worked as it should. I can upload the video to YouTube if anyone would like, but since it worked fine in the video, I'm not sure what good it would do. If I notice it doing the same things in the future, I can record another video and upload it, but I think Jan's advice was the correct solution after I double checked the slider for CWS.

 

On a side note, what is the proper procedure for descent? Is VNAV ok to be used given the FMC calculations, or vertical speed? It seems VNAV descent is working ok for me, but on approach the speeds in the FMS are too high, so I adjust those along with any altitude constraints and it seems the plane struggles with the auto throttle as its jumpy and doesn't maintain the set FMC speed like it does in climb. Is this a known issue and something that is being worked on or no?

 

Chad

Edited by Popcorn

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I would suggest you put the CWS nullzone slider to the right, it won't hurt at all and if you controller is sending noise/spikes it will prevent from interfering a/p operation

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Hi Popcorn,

happy to hear that things work out better now!

For initial descent you can use VNAV, but keep a close eye on it and it´s calculations. For the final approach you must use MCP SPD and either LOC/GS (for ILS) or V/S for NON-PREC or RNAV approaches (using LNAV or HDG SEL). VNAV is not certified for approaches in the 737-300...and while it would work on the real one, it does not (yet) in ours.

Cheers, Jan

 

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