Since I have occurrences where I hit PROF and nothing happens either on the FMA or the FD/autopilot, I try to understand the reasons for that phenomenon.What are the requirements so that PROF can enter the engaged state (i.e. dependance from lateral path, spacial distance from calculated vertical profile,...)?

You should be aimed on an intercept to the line for NAV to better capture the lat path (or use direct to, which will draw a line right off of your nose so you can't miss, even if you're pointed away from the fix), and you must hit PROF above 400' AGL.

Since I'm a passionate hand flyer, I often don't follow the lateral path especially during the first flight phases. Same goes for the vertical profile where I'm way off the computed path. Now, re-joining the lateral path is quite easy to do. I even think that lateral guidance is very generous, so that NAV engagement would turn the plane more or less towards the next waypoint (if not, there's still the direct to feature). More difficult is re-joining the vertical profile: Even when climbing and in the vicinity of the lateral path, I have situations where I feel I'm not too far off where I should be vertically, but klicking PROF doesn't do anything and the plane stays in flight level change mode.So, I guess there are some restrictions for PROF engagement and certain conditions must be met so it can be activated. And that's what I want to know because I don't find anything in the manuals. As long as you fly "by the book" and do the regular procedure (take off, activate autoflight with nav and prof etc.), everything is okay. But beware if you don't do all that and fly like me, off path and all by hand...

You may be a passionate flier, but you do not seem to be an accurate one. Why would you bother to prepare a detailed flight plan if you are not going to follow it. Hand flying or A/P, your flight plan doesn't (or at least shouldn't) change.

I don't remember exactly the parameters that prevent you from arming PROF mode after some handflying...I have to read again the AP limitations in manual...But there are two suggestions for you:1) Arm the PROF mode at 400' feet AGL and follow it manually in hand flight...that's the best way, because when you will engage AP1/2 all the FMCs modes are armed and activated...2) Remain in FLC mode until cruise, the logic behind PROF and FLC is very similar, except for the required speed that is controlled in the first mode by the FMS and in the second one by the captain...The pilots tend to follow the FD when in hand-flying so, set the FD modes in a way you can follow the lateral route and the vertical path...Cheers,

Since I'm a passionate hand flyer, I often don't follow the lateral path especially during the first flight phases. Same goes for the vertical profile where I'm way off the computed path. Now, re-joining the lateral path is quite easy to do. I even think that lateral guidance is very generous, so that NAV engagement would turn the plane more or less towards the next waypoint (if not, there's still the direct to feature). More difficult is re-joining the vertical profile: Even when climbing and in the vicinity of the lateral path, I have situations where I feel I'm not too far off where I should be vertically, but klicking PROF doesn't do anything and the plane stays in flight level change mode.So, I guess there are some restrictions for PROF engagement and certain conditions must be met so it can be activated. And that's what I want to know because I don't find anything in the manuals. As long as you fly "by the book" and do the regular procedure (take off, activate autoflight with nav and prof etc.), everything is okay. But beware if you don't do all that and fly like me, off path and all by hand...

You may be a passionate flier, but you do not seem to be an accurate one. Why would you bother to prepare a detailed flight plan if you are not going to follow it. Hand flying or A/P, your flight plan doesn't (or at least shouldn't) change.

While I appreciate your wanting to actually fly the aircraft, as so few do, Paul does make a point. AP or not, precision is still key. If you file it, you should be able to fly it within the appropriate limits (though they are rather large in some cases: airways being 4nm laterally on each side of the centerline as an example).

You may be a passionate flier, but you do not seem to be an accurate one. Why would you bother to prepare a detailed flight plan if you are not going to follow it. Hand flying or A/P, your flight plan doesn't (or at least shouldn't) change.

Correct :( Sometimes I just "simulate the unexpected" :smile:You get fancy results when doing so... Anyway, thank you all for your efforts to help me.