I recently started to fly the PMDG 737-800 NGX. 

 

I am having trouble using the autopilot.

 

I entered a flightplan in the FMC with SID, route, but leaving the STAR empty as i don't know which runway i will be landing yet. Usually i enter the STAR and the arriving runway once the destinations ATIS is giving the information.

 

I fly from MILANO MALPENSA (LIMC) to FRANKFURT AM MAIN (EDDF).

 

Before taking off i set both FD on and entering altitude, speed and heading.

 

Once i have taken off i wait before passing 1000ft to engage the autopilot with pilots 'CMD', but it WONT ENGAGE. I am not touching the yoke a

The green lights flikkers just the time a press the button, but it does not stay on.

The auto trottle is working with speed. But altitude, vertical speed, heading, VNAV and LNAV are not working.

 

I am wondering what is going wrong here. Am i missing anything or any other setting? What are the correct steps to engage autopilot after take-off?

 

I flew the flight manually using the trim.

The aircraft must be in correct trim before the autopilot will engage. Was it *properly* trimmed before trying to engage?

 

Otherwise your controller might be spiking, try selecting the control override in the options?

@ James Benett,

 

thank you for your reply. to be honest i don't know what you mean with trim settings. How do i select the control override options?

And how do i trim the plane before engaging?

 

I also tried another simple take off without entering a flight plan. There i could engage the autopilot.

 

PS: i am an amateur with very few knowledge

Are you using a joystick or the keyboard to fly the plane? If you're using a joystick, assign two buttons to elevator trim, one to increase it and one to decrease it, then you can trim the plane as you fly. Once it's correctly trimmed the autopilot can be engaged.

 

Before trying to engage CMD which autopilot modes did you have selected? 

I am using the saitek yoke.

 

I know how to trim. I am trimming manually in the virtual cockpit.

 

But is there any standard take off trim setting? How do we choose the correct trim position?

 

 

Before trying to engage the CMD i just set the two FDs

The FMC will calculate take off trim setting for you in the TAKEOFF REF page once the PERF INIT page is complete. You then enter the number it gives you in the trim window beside the thrust levers. Try and find the relevant section in the manual, it will explain it a lot better than I can without pictures.

ok, i will try to do this.

 

But will it avoid the AP to engage if the correct trim setting is not set?

The autopilot will not engage unless the aircraft is in correct trim, that applies to all phases of flight not just after takeoff. If you were to set the wrong trim for takeoff but re-trimmed it afterwards, it should still engage the autopilot but correct trim should be set for takeoff regardless.

I am using the saitek yoke.

I recently purchased the saitek yoke and experience the same issue if I'm applying any control input at all. You either need to be trimmed so you require no control input while engaging the AP or turn off realistic AP engagement in the PMDG menu.

 

Mike

I recently purchased the saitek yoke and experience the same issue if I'm applying any control input at all. You either need to be trimmed so you require no control input while engaging the AP or turn off realistic AP engagement in the PMDG menu. Mike

It should behave like that regardless of the brand of yoke, it's not an issue, that's how it is in real life. It won't engage if there's pressure on the yoke because that means the aircraft isn't trimmed for it's current attitude.

Just to be clear, trim position itself is not AP engagement criteria. Take off trim position is irrelevant too, you are gonna to retrim it as soon as you establish climb.

You can go into the FMC aircraft options and change the "AP Realistic" setting to off. I had to because one of my controllers is preventing it from engaging no matter how many times I calibrate them.

It should behave like that regardless of the brand of yoke, it's not an issue, that's how it is in real life. It won't engage if there's pressure on the yoke because that means the aircraft isn't trimmed for it's current attitude.

I didn't intend to make it seem like an "issue" with the Saitek yoke. I only meant to confirm my experience that if you're applying any control input you cannot engage the autopilot. I also said you can avoid that by turning off realistic autopilot engagement in the menu system if one chooses too.

Just to be clear, trim position itself is not AP engagement criteria. Take off trim position is irrelevant too, you are gonna to retrim it as soon as you establish climb.

 

Yeah, but being correctly trimmed is part of the criteria is it not?

 

I didn't intend to make it seem like an "issue" with the Saitek yoke. I only meant to confirm my experience that if you're applying any control input you cannot engage the autopilot. I also said you can avoid that by turning off realistic autopilot engagement in the menu system if one chooses too.

 

I know, it was more for the OPs benefit so he didn't think it was an issue with his yoke and end up buying a new one.

i will try now. I guess i haven't completed the FMC with regards to the TAKEOFF REF and haven't set the trim correctly.

 

What if you engage the AP at cruising altitude? which trim position do you need to set in order to engage AP at that time?