Hi, sorry for my English. I'm trying to figure out what has happend with vert. profile after LI730 waypoint. Just before this waypoint vert. dev was 0 and just after vert. dev became 4722 and 738 has lost vert. path. Descend forecast was accurate. After LI730 I turned on V/S mode (-1500), descended to FL050 and aircraft captured ver. path again. I use FSX SP2 and PMDG 737-800NGX 1.20.8885. See screenshots: before and after.

 

Hi Max:  This is a very common problem with the PMDG FMS, it is better in the newer QOTSII B747 but they still need to do a major update to the FMS and AFDS code to fix this a a few other problems PMDG has.

When I get one of those vertical path discontinuities I will usually revert to either LVL CHG or V/S and forget about VNAV.  The vertical path indicator window you have shown opened on the ND is an excellent choice to manage the descent. 

Dan, for the first time I thought that I missed inscrease in vert. dev., for the second time that descend forecast caused this problem, for the third time that I did something wrong with FMC setup🙂 Thanks for help!