I recently hit the "z" button on my keyboard in-flight, thus disengaging the autopilot. However, when I went to reengage the autopilot via the CMD switch, it would not reengage. I assume that there is some kind of system that is stopping me from reengaging the autopilot? How do I reengage it without resetting the flight?

Matthew Lewandowski

Hi,

Is your Z key simulating the AP disconnect switch on the yoke of the AP disconnect bar on the MCP?

If the disconnect bar is in the lower position, you cannot engage the AP.

Also check that your controls are at neutral position and the aircraft trimmed. 
These are the two situations preventing the AP to be engaged that come to my mind.

I recommend you assign the autopilot disconnect in the PMDG Options keycommands and use that. The engage autopilot and disengage autopilot should be two separate commands. Do not use the disconnect bar mentioned by Romain, it is only used in non normal cases.

The Z key is set to the FSX default toggle autopilot, so it serves the same function as hitting the AP master switch on the MCP. This has also happened before, when I was taking off once. I had set the autopilot CMD switch on, and then I took off using the auto takeoff thrust button located on the top of the thrust levers. I also had the same issue.

As advised by Dan, you should assign the key to the AP disconnect switch in the key commands through the CDU.

As suspected, the Z default sim assignment must put the AP disconnect bar in the lower position hence the impossibility to reengage the AP.

12 minutes ago, SoloPilot said:

I had set the autopilot CMD switch on, and then I took off

Do you mean that you engage the AP on the ground before taking off? If ever it is possible this is not the correct procedure. The AP should be engaged only above 400ft AGL.

2 hours ago, Budbud said:

Do you mean that you engage the AP on the ground before taking off? If ever it is possible this is not the correct procedure. The AP should be engaged only above 400ft AGL.

Yes, I did that. I learned that it wasn’t correct procedure, but still I couldn’t reengage the autopilot. Also, the AP disconnect bar is not in the lower position. 

What exactly happens when you try to reengage the AP? What alert, display?

And what is displayed on the FMA for the active/armed modes?

2 minutes ago, Budbud said:

What exactly happens when you try to reengage the AP? What alert, display?

And what is displayed on the FMA for the active/armed modes?

Nothing alerts when I try reengaging. It just doesn’t do anything when I click the CMD buttons. Nothing shows up on the FMA for “CMD Arm” like it should

Can you post a screenshot of the MCP and PFD?

Ok so I figured out that shutting off both FDs then turning them back on allows the autopilot to be armed again.

I don't remember for the NGX but on the 747 an invalid pitch/roll mode may prevent the engagement of the AP. Recycling both FDs reset the AP modes so it may be the explanation. However in this case you should have the red alert autopilot on the EICAS along with the invalid mode struck through in yellow on the FMA.

Or maybe the default FSX autopilot assignement just messes up with the AP of the NGX. In any case, I would suggest not to use the Z key anymore in the NGX or delete the default assignement in the FSX controls and assign it to the AP disconnect switch in the key commands in the PMDG setup via the CDU.

11 hours ago, Budbud said:

I don't remember for the NGX but on the 747 an invalid pitch/roll mode may prevent the engagement of the AP. Recycling both FDs reset the AP modes so it may be the explanation. However in this case you should have the red alert autopilot on the EICAS along with the invalid mode struck through in yellow on the FMA.

Or maybe the default FSX autopilot assignement just messes up with the AP of the NGX. In any case, I would suggest not to use the Z key anymore in the NGX or delete the default assignement in the FSX controls and assign it to the AP disconnect switch in the key commands in the PMDG setup via the CDU.

Yeah, that's what I figured. I just flew the NGX again, and I used the takeoff thrust button. I didn't arm the CMD switch on takeoff. When I retracted the gear with the G button, I also heard a click as if a switch flipped in the cockpit. I don't know what it was, but I continued on. I went to arm the autopilot CMD, and I had the same issue. I tried resetting the FDs, and that didn't work either. I'm stuck again without any solution.

Hmmmm, sometimes when I try clicking the button repeatedly, the green indicator light flashes on for a fraction of a second. It's like it almost can come on, but it won't.