So I was flying the MD11 from Princess Juliana to Schipol and everything worked fine on the FMC. The plane also took off with no issues, and LNAV engaged. However, VNAV (prof) never did but the throttles are moving themselves and the PFD showed prof armed. Despite this, I can still control them manually. I would be grateful I someone could provide a solution. It seems that the queen is much more easier to fly lol.

You can arm the PROF on the ground or engage it once in the air above 400 feet.  If your PFD shows PROF armed, but is not engaging, try pressing the PROF button again.

 

You need to have at least the A/P or FD engaged to operate PROF. Normal procedure is to have the FD engaged at all times.

thanks for your reply

Moreover, I would like to ask if I should insert my cruising altitude in the altitude selection bar??

 

 

Moreover, I would like to ask if I should insert my cruising altitude in the altitude selection bar??

If by altitude selection bar you mean the altitude window, the answer is yes. But you can't  just dial in any altitude you like. Your cruise altitude or altitudes need to entered on page 1 of FL PLN-INIT and you need to refer to the ECON CRZ page to see what is the appropriate altitude to be currently be at. 

Try the very helpful Tutorial that Tabs went to a lot of effort to produce. It will answer every question.

If PROF ARMED is shown on PFD it should ARM at 400 ft. If this does not happen, on the real airplane, there could be some problem in the ground/flight shifting or some data is missing on the FMS.

But may be it s just a problem on this flight. try to reset the flight doing everything from the beginning