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AP problems : ALT SEL not stop climb, HDG not possible, NAV not capture, GPSS/HDG always off

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I use x-plane 11.55 on iMac.

I have some problems with AP and MU-2B OEM or GNS aircraft :

- ALT SEL button I set altitude and activate AP and ALT SEL. ALT SEL indicator move to ARM. Aircraft climb and at the selected altitude the ALT SEL indicator move to CAP but aircraft continue to climb

- ALT button : impossible to activate ALT hold

- NAV button : (similar to ALT SEL problem). I set NAV and CDI to VLOC. When aircraft capture LOC, NAV button indicator move to CAP but aircraft continue to turn.

- HDG button : impossible to activate HDG, and the GPSS button always OFF. impossible to move GPSS or HDG.  GPS CDI is on VLOC

Thanks for your help


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Hi Nicolas.  There is a "roundout" phase of the altitude capture where the CAP annunciator on ALTSEL illuminates for a short bit while the aircraft levels off....and a few moments later the ALT capture mode should kick in and indicate.  If you press the ALT button during this roundout phase...then that ...MAY... create a problem...I'd have to check again.    X-Plane does not  support the concept of  a "capture roundout" phase, only capture, which caused me to have to do a bit of a "dance" programmatically to get the annunciators to match the real thing....it seems I recall there is a small window of time during this roundout/capture phase where you cannot activate the ALT mode.  The aircraft should continue to climb a slight bit after the CAP annunciator illuminates, but shortly after, should level off at the selected altitude.   Does the aircraft continue to climb past the target altitude set if you just let the system do its thing?

Regarding the NAV, I can't say for sure what your issue is completely from your description.  the VLOC setting has no bearing on the LOC capture, it only controls what signal is fed to the GNS CDI needle.  The NAV mode will capture the localizer a bit outside the beam, so depending on how far away you are from the LOC source as well as how fast you're approaching its centerline and at what angle will all have influence on what the AP tries to do...in some 'tight' cases, it can't make the capture properly and the AP response will overshoot and you have to readjust.  The OBS setting also is an input to the LOC capture so it needs to be set as well for a good capture.

Regarding HDG button,  I haven't seen that issue.  did all these issues happen in one flight session?   I'm wondering if maybe one issue cascaded into the others.


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Hi tkyler.

I confirm i press only ALT SET. ARM annunciator illuminate. Near the desired altitude, the CAP annunciator illuminate. The aircraft continue to climb after the altitude selected. The CAP always stay illuminated, aircraft climb …

Note that the ap stby annunciatore extinguish when i press ALT SEL at the beginning…

it’s very strange. AP button (HDH, VS) seems not work. Nothing happens when i press button. No annunciator illuminate :-(

For the NAV and APR button, ARM annunciator illuminate when i press button, and AP STBY annunciator extinguish (OK was illuminated before)

i wil try to make a video






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Sorry to butt in and probably not help, but I remember having this type of problem some time ago as well.
I don't remember the details anymore, but if I remember correctly, the problem was the incorrect assignment of commands to the hardware used - I use honeycomb alpha and bravo. This caused conflicts and resulted in similar "abnormal" AP behavior.
Maybe this problem also applies to your situation ?

... it seems to me that the problem was with the: AP PITCH TRIM WHEEL and the commands assigned:


Edited by Bulva
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I think i have found the problem.

I use Lua script to simulate the ap turn knob. for this I use the dataref "xscenery/mu2b60/manips/ap_turn_knob".

if i use dataref("xspr_df_mu2_ap_turn_knob", "xscenery/mu2b60/manips/ap_turn_knob", "writable") then AP is KO. the AP button annunciator is illuminated but auto pilot does not work. 

if I don't use the dataref "xscenery/mu2b60/manips/ap_turn_knob" writable, autopilot work correctly.

I noticed that if AP HDG is enabled, and if I use AP turn knob then HDG is automatically disabled. I can't use the autopilot until the AP TURN KNOB is centered at 0. All autopilot is disabled (ALT SEL climb, HDG, VS, ...) if the value xscenery/mu2b60/manips/ap_turn_knob is not 0.

So I think using the dataref("xscenery/mu2b60/manips/ap_turn_knob","writable") consider permanently using the AP TURN KNOB and disabling the autopilot


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