VNAV & AT DISENGAGING in flight

[Gnacino 48]

I did two tut1 flights and everything ok. I tried a local flight, KABQ-KORD, got the fmc loaded, v speeds showing on the pfd, armed the LNAV, VNAV, and the auto throttle. I was in cruise FL 350, about ten minutes into the flight, and I got a shaker sound, overspeed. The VNAV was disengaged, and so was the autothrottle. No matter what I did, could not engage either one. I got the AT warning on the panel. I looked at the throttles and the #1, the left lever was not moving as the right one was. I physically moved the left throttle on my Goflight TQ6 so it was in sync with the right lever. then I was able to engage the VNAV and the AT. This sequence of events happened four more times in flight at various times. Not sure what caused this. Anyone have any ideas?

 

Thanks,

 

Gnacino

[Rick_Butler 0]

Weather program causing a wind shift and overspeeding you causing AT and VNAV to disengage?

[Gnacino 48]

I am using REX. I'll pay attention next time the weather loads and see if that's it. If so how do I fix that? Is that a REX issue or PMDG?

 

Gnacino

[RWFeldman 159]

If you have throttle override disconnect AT enabled and get a spike from the throttle this can occur also. of course when AT disengages so does VNAV.

[Gnacino 48]

10-4

 

Gnacino

[Lek767 37]

about ten minutes into the flight, and I got a shaker sound, overspeed.

 

Which one of the two was it: a clacker sound (overspeed warning) or the stick shaker (stall warning)?

 

 of course when AT disengages so does VNAV.

 

Sorry, but that's incorrect. One can disengage the autothrottle independently from VNAV, and vice versa. A hardware throttle spike, especially one that triggers the thrust reversers, can indeed cause the A/T to disengage, though.

[Gnacino 48]

Clacker sound, overspeed. I did a couple short flights and noticed that it always happens when REX is injecting weather. If I run FSX without REX, it does not happen. I posted on the REX forums with this issue as well. I don't know if this is a PMDG or REX issue. The throttle does spike, it's always the #1 throttle, I sync it manually, then I can engage the AT and VNAV.

 

Gnacino

[mounty 13]

Hi,  How are your throttles set up, through FSUIPC?  I had the same problem and I found the answer in this forum.  Set the axis in FSUIPC, but do not, repeat, do not calibrate them.  This will stop spikes in your throttle so it won't disengage, and you can move your throttle levers back to the idle position.  Set the FMC A/P to Never in the manual override section.

 

Rob

[Spidierox 4]

Well, first I stopped using REX and now use ASE and don't have the speed spike issue anymore with ASE among other improvements.

Injecting the weather always had this issue with REX - I believe even from REX v2 onwards but certainly from REX v3 (Essential, Essential Plus..)

 

Second, try calibrating your stick including increasing null zones. I don't use FSUIPC as - if I recall correctly - it is not recommend by PMDG but instead calibrate the hardware directly.

[pete_auau 1,152]

 

 

I don't use FSUIPC as - if I recall correctly - it is not recommend by PMDG

 

This  is  a first I heard off pmdg saying  don't use fsuipc,

[Spidierox 4]

 

This  is  a first I heard off pmdg saying  don't use fsuipc,

I did not state "no use" I said "recommended" in the context of calibration the joystick.

 

Also, check the introduction manual of the 737NGX:

 

* The goal of Microsoft’s FSX development team was to create greater

interoperability between the FSX platform and add-on developers like

PMDG. In theory this should all but eliminate the requirement for users to

install and use FSUIPC as an interface between complex add-ons and

the FSX platform.

* The PMDG 737NGX is fully compatible with FSUIPC except that

we recommend that you do not calibrate your flight controllers

through FSUIPC. We recommend that you use the

driver/software that comes with your hardware. (Calibrating

through FSUIPC may not cause any problems, but in certain

circumstances with certain hardware we found that problems

existed that could only be resolved by having the user conduct

the calibration via the driver/software.

[Gnacino 48]

I'll try that, not calibrating thru FSUIPC.  I posted on the REX forums, but they deleted my post because I "piggybacked" my problem with someone else having the same issue.  Not a big fan of their help forum.   I will look into the ASE program but am not familiar with that.

 

Thanks,

 

Gnacino

[scandinavian13 5,192]

 

 

I posted on the REX forums, but they deleted my post because I "piggybacked" my problem with someone else having the same issue.  Not a big fan of their help forum.   I will look into the ASE program but am not familiar with that.

 

No sense in buying new software.  If you have a registered version of FSUIPC (I'm assuming you do from the other posts), just enable wind and pressure smoothing.

 

Done.