Hello :( I've a problem with the PA on the PMDG J41Before takeoff, I set the PA ("set" but "off" of course) on "LNAV", "ALT SEL", "VS" and "HDG".After Takeoff, I engage the PA but it's impossible for me to engage the Navigation mode ("NAV" button).I miss one thing (a condition or a operation) I think, but what ?Thank for your help :)

What is the AP (or PA?) supposed to navigate to? Have you entered a flight plan for LNAV to follow? Maybe you need to turn to an intercept course to fly to the first fix on that flight plan? Are you using a SID? Maybe it uses a vectors command or any number of reasons. Need more info.

Did you set your EHSI to "LNAV"? If you didn't switch the EHSI it would be on the default VOR1 setting.

Thank for your answers :( I've entered a flighplan in the FMC, with SID, STAR and approach before start. Yes, before the takeoff I set the EHSI to "LNAV" (BRGs on "LNAV" and "LNAV" Mode) and the AP to "HDG" (synchronised), "ALT SEL" to 7000 fts and "VS" 1500ft/min. PA OffAfter the takeoff I engaged my AP and during the climb, I wanted to engage the NAV mode and ...it was impossible.

For some reason, I believe you have to have the Yaw Damper on for the AP to work. Maybe that's the problem?

Are you sure ?I'll try it tomorrow

Did you set the EHSI to "Map"? Don't know if that's necessary, it's just a guess.About 3 hours ago I had that problem, too. After pushing "map" and "LNAV" the "NAV"-Mode armed.

No I didn't set the EHSI on "Map". Strange if it's necessaryBut maybe it's a bug ? I didn't found in the manual anything about this "problem".Are there any others manipulations to do ? In a precise order ? In a precise time ? To activate the NAV mod ?

You shouldn't need to go to "map", but it is handy to see the flight plan to insure it is properly configured into the FMS. I assume you have the "to" and "from" set for the first leg on the nav page on the FMC?After that I don't think there is much we can speculate without seeing it first hand or with pictures, does this continue? Might have been a one off bug.

I think it's not bug.I just launched a new flight.I've set my FMC and my AP like yesterday but on the active runway and engine started. Not in a Cold and dark situation.With the same operations, the NAV mod has worked correctly this time.I think that when I begin in a cold and dark, I forget something. But what ? That is the question :(

Well the problem might be how the flight is started, the J41 doesn't have a panel saves and you can get some odd results when you attempt to make your own, usually best to start with a default aircraft and shut everything down then load the J41 in it's place.

Thank you very much. :( Yes I think a mistake. All work well now. I don't know why, but 2 flights without problem this morning. Even from the same Cold and Dark situation. Maybe I was too far from the 1er point heading after the takeoff for the AP. It's possible ?