Autopilot weird behavior (disconnecting and not following FD commands)

[ivo09 23]

Hello, on my last flight I have a couple issues with the autopilot which I couldn't work out myself so I came to ask for help. 

 

First, shorty after takeoff the autopilot disconnected during climbout. At 10k feet it suddenly disconnected and the horn sounded. The aircraft was flying normally. I reconnected and it was ok until it disconnected again passing 15k. Again I engaged it without a problem. The aircraft wasn't stalling, overspeed, anything which may make the AP disengage. The was no control inputs from my joystick.

 

Secondly, as I reached cruise altitude the aircraft started slowly banking right until it flew off course. The FD bars were commanding a left turn but the AP just let the aircraft drift into a shallow right bank. I disengaged LNAV and set a heading. The AP started a very shallow left turn and wouldn't exceed 2* of bank. The bank limiter was set to 30. 

 

 

Im utterly confused. Please help me understand what the aircraft is doing?

[downscc 1,327]

How did you create this flight?  Did you load a saved flight and if so can you reproduce this problem?  Did you create the flight from a default start?  Did you load the PMDG aircraft into the simulator from the Free Flight screen (FSX) or did you load it when another PMDG aircraft was already loaded?

 

Check your PMDG Options for the simulator and make sure you have the settings you want for the controller and how it reacts with the A/P, an A/P disconnect for no apparent reason is usually a controller.

[scandinavian13 5,192]

The AP may kick off if you have a trim axis that hasn't been neutralized.

[ivo09 23]

The flight was started from create a scenario in p3d and the joystick ap override is turned off.

 

@kyle

Both aileron and rudder trim was untouched.

[downscc 1,327]

 

 

Both aileron and rudder trim was untouched.

 

Yeah, a trim imbalance would of prevented A/P engagement in the first place; but, maybe your controller is noisey or spiking?

 

There is no disable A/P disconnect for the joystick, only for throttles.  That's why both Kyle and I are suggesting a problem with your controller.  Put it this way, if there was a problem with A/P normally staying engaged there'd be hundreds of forum posts on this subject.  There's not, so I'm pretty confident there's something in your setup behind this.

 

The FMA in your original post is normal, CMD B is active, HDG SEL is set to 040 and yet she is off on her own, quite illogical.  That's why I asked about how the flight started.

 

Can you reproduce the problem?

[ivo09 23]

I can try to reproduce the problem tonight. In flying with a relatively new x55. I dont believe I've encountered this issue with the 777 but I havent flown much frequently. How can I monitor if my joystick starts spiking? Everything looks nice and centered in the software and hand flying has never been a problem.

[skelsey 765]

I'm not an expert on the 737 -- but is is normal to have LNAV/VNAV annunciated above the ADI when the FMA is (as expected) displaying HDG SEL?

[ivo09 23]

Hey, I'm continuing to have issues with the NGX. Soon after reaching cruise, the autopilot starts behaving weird. Here it is starts making an uncommanded right turn until the plane stalls. If was absolutely fine a minute ago, and out of nowhere the plane becomes uncontrollable. I'm flying the T7 with no problems, only the NGX has this problem.

 

 

Perhaps a reinstall is in order?

[Budbud 227]

Try loading the airplane with the default panel state to rule out any corrupted panel state maybe?

[ALF1 15]

Youre definitely not doing anything wrong. FMAs look fine. If you dont have any autopilot failures active or enabled I would do what Budbud says. I am thinking this is a wrongful installation issue.