I have scanned the forum but not found the explanation of this unexpected behaviour.When directed to descend from my cruise lvl (22k) to 12,000ft I used V/S, which disconnected VNAV. After reaching 12,000 I wanted to get back to VNAV in order to optimize speed: I accepted 12,000 as the new crz level (FMC had already entered it) and selected VNAV, expecting altitude to remain steady. However, a/c started a very slow descent. I thought it would be a short transient but it kept going far enough that I had to revert to LVL CHG to avoid upsetting my friendly Radar Contact controller.QNH was standard 1013 so it could not have been a FL vs Alt issue. I also doubt this was the planned VNAV descent since I was already so far below my original planned CRZ alt.I'll try to reproduce it and note down some details when I have some time but I thought someone may know the answer.Thanks.Phil Thibault

You might find a clue on the LEGS page and note which fix and crossing altitude the FMS thinks it is flying to. Generally, once you start getting altitude constraints from the controller you drop VNAV altogether and start using MCP SPD and V/S or ALT, at least that is what I do.

You might find a clue on the LEGS page and note which fix and crossing altitude the FMS thinks it is flying to. Generally, once you start getting altitude constraints from the controller you drop VNAV altogether and start using MCP SPD and V/S or ALT, at least that is what I do.

The LEGS page, of course! Never thought of it - still new at this.Thanks, Dan.PhT

The best thing you can do for yourself to learn the fly the PMDG 737NG is;1. Read all of the manual2. Find someone who can send you a copy of Timothy Metzinger's "PMDG 737NG Advanced Tutorial V2". This is, by far, the best tutorial for the plane that I've ever seen. Tim had to remove it from public distribution due to some Jeppeson charts being in it. Do all five flights in the tutorial and you'll really learn how to fly the plane properly. PM me if you can't fine a copy of the tutorial.Dave

I have Tim's tutorial. It is indeed an excellent reference.Thanks,Ph

I have Tim's tutorial. It is indeed an excellent reference.Thanks,Ph

Would you be willing to email it to me?

Would you be willing to email it to me?

It is as large as it is good! Check your mail and/or do a Google search.