Sorry to bring back a memory of "the other thread" on this, but it was too long and probably not my exact problem (which may be simply a blonde moment(s) on my part).Bought 737 NG 3 days ago. Been through the tutorials and scan read most of the FMC manual with detailed reads of various areas.During the tutorial flight I had a few problems that I put down to just poor systems understanding on my part. The A/P modes started disengaging closing in on approach, I failed to notice this and ended up going missed, runway was in sight and I was still at 2000 ft.Going missed I hit the TO/GA mode and set the MP altitudes etc. The FMC had the correct MP as the active route, but the LNAV and VNAV would not re-engage. Tonight, after a long day programming ASTRA1B STAR and the MAYFIELD transitions into the FMC I flew from Belfast(EGAA) to Gatwick(EGKK) via IOM, WAL, HON.TO, (intercept) departure, Climb, crz all went well, i oops the decent by not setting the dash panel ALT down to the decent bottom, but the autopiloted slam dunked nicely with the speed brake out. Entering hold at ASTRA and my problems started.HOLD AT ASTRA 220/7000Worked... however, the AIP chart for transition drops us in the hold to 4000, so I added another leg as:HOLD ATASTRA 220/4000I found the HOLD page and clicked >ExitHold then Exec and set the ALT to 4000. The FMC still showed the old hold. Trying a few things to correct this and I finally got it to move to the next hold. However, it refused to decend to 4000. VNAV and LNAV were on and appeared working. 4000 (purple marker) was indicated in the main display but no V/S was showing. I let it go around the hold one more to make sure it wasn't waiting to cross ASTRA. Then I disengaged VNAV and descended to 4000. Reengaged it and it once again tracked altitude OK.It appear however that when I reached 3000ft the VNAV disengaged, yet there was a descent to 2000ft as the next leg. Speed was at 200, but the next waypoint was 180. The error in the FMC was "Check MCP ALT", which I had set to 2000.When I went missed, the TO/GA worked, but climbed me at insane rates to 3000ft. Almost stalling it, the anti stall kicked in and firewall the throttles at 110kts. When it leveled at 3000, the correct course for the MP was in the FMC as the ACT, but VNAV would not re-engage.Can someone explain to me the conditions on which the various VNAV, LNAV holds will engage, disengage automatically and reengage? I know I am doing something wrong.Oh, and.... can you explain how to have 2 holds one on top of the other and descend from one to the next using the FMC HOLD page...Thanks.Paul Campbell

"The A/P modes started disengaging closing in on approach,[/b}" This happens when the G/S becomes active. There are other reasons for A/P disconnecting but this is what most will encounter and is what the real aircraft does. Of course you can take VNAV down but I don't. As for you holding question, maybe a real pilot can step up and answer. Off the top of my head I am not sure how that's done (descending in a hold) etc. I will say that regardless of what a chart says you cannot change altitude without ATC permission. Best Wishes,[h4]Randy J. Smith[/h4][h3]P M D G's 747-400[/h3][h4]coming to a runway near you[/h4][/font color]Caution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |

"The A/P modes started disengaging closing in on approach, I failed to notice this and ended up going missed, runway was in sight and I was still at 2000 ft"As Randy says, this is supposed to happen. The light in the APP button goes out when G/S captures. This does NOT mean it has disconnected. All autopilot modes are displayed in the Flight Mode Annunciator (FMA) area of the Primary Flight Display (PFD). This is where you shoudl look to see what is engaged at any time. The lights in the buttons are there to tell you one thing and one thing only - You can disengage this mode by pushing the button! the APP light goes out because once G/S has captured it cannot be turned off by pushing the button! You will note that even though the APP light is not on you still have VOR/LOC and G/S in the FMA on the PFD .As for the hold even as a real 737 pilot I have only had to do a hold once and that was for a fairly short time and involved no descending. Unfortunately because of this my knowledge is a little rusty but here's one way you 'could' do it!Once in the Hold using LNAV and VNAV, if told to descend simply push LVL CHG or V/S after setting the new level in the MCP. VNAV will come out and you will descend while maintaining the LNAV profile! I am on the Murcia flight tomorrow which inevitably involves holding while the Spanish air force recover their little fighter jets so I will endeavour to look into it for you and report back tomorrow night!Kris