737NG Autoflight Concern
Hello all,
I've been trying to master the 737NG for a while now, however I have one question which I'm trying to resolve. After I depart, the FMC is programmed to reach certain altitudes when crossing certain waypoints, however, sometimes, I reach that altitude before I reach the waypoint, and so the plane doesn't climb again, until reaching the next waypoint. Also, VNAV deactivates after reaching the altitude, and then I can't reactivate it. I read the manuals, and it does mention what VNAV is used for, but how come I can't activate it during certain phases of flight. I apologize if this sounds a bit stupid coming from me, but I'd really like to learn to fly this aircraft accurately. Your help is very much appreciated in advance 😉
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Ah, well, if you have your MCP set for certain altitudes, it doesn't always like when that gets changed, I've found that I have to re-set the VNAV button to get it to continue.
If you program in the waypoint restrictions in the LEGS page, you should be able to set your MCP altitude at cruise altitude and it will still meet those requirements, and hopefully proceed after that. I've never used it on the climb out though, so I'm not sure.
Hmm, I just tried again, and I must be doing something wrong, so I'll make a quick example of what I do when running through the FMC before the flight.
After I've set my DEP / ARR information, and selected calculated VSpeeds/Trim, etc, I go over to the legs page. Now, seeing as how I alreaady went through the DEP process, the SID waypoints are already entered, so I just go down, and enter whatever waypoints I have left. It seems like the FMC automatically calculates altitudes for each waypoint, and I don't know how to disable that, which is what the problem is.
Now, upon departure, the aircraft climbs up to 10,000, then holds. I didn't wait to see if climbed any higher upon reaching different waypoints, because it would take too long, and I had little patience 
-- Anyways, once it reaches 10,000, VNAV is disabled -- When I try to enable it again, it says "Check MCP Alt" -- Is it possible for you to tell me what I'm doing wrong. Thank you for your co-existance with the thick pilot that I am. 😉
Check MCP altitude means that the Flight level (or level of the next waypoint) doesn't match what's on your Autopilot panel.
Legs will automatically calculate each waypoint's flight level, but the ones in BOLD are the "restrictions." Everything else is more-or-less just flexible guidance. So for instance, if you know you need to hit a waypoint at 10k feet, you enter 240/10000...and it should show up in bold. It will now do everything it can to hold 240kts and 10k feet at that waypoint. If you're not happy with a restriction, simply hit delete, and then the restriction.
Okay, so I've know gotten the aircraft to climb above 10,000 (it's embaressing to know what little we actually do with the freewares), however, one last question (I think). How can I get to climb to 35000, and pass through the waypoints as it pleases, eg. If I wanted it to keep climbing to FL350, it's unrealistic to place that value in the first waypoint, which is 20 miles, away, because that would mean it would try and climb at or over 6000FPM...If I place the value of FL350 in another waypoint, the FMC automatically calculates what altitudes it should be at when passing through the waypoints that are preceeding the waypoint at which I reach FL, and so if I arrive at the specific altitudes before reaching the waypoints, the aircraft will stop climbing, until it passes that waypoint (Whew, I hope that made sense 🙄 ). Right now, I'm just playing guess and check, trying to get the aircraft to climb at a realistic rate 
If I haven't said so already, thank you very much for your kind help. 😉
I think you're entering your cruise altitude in the wrong place. When you're doing your Perf Init, you should see a spot for your cruise altitude. If you do it there, it's no issue, just set your MCP to the restrictions ATC gives you and set it up to your flight level once cleared. It'll climb to where you need to, occasionally requiring you to re-set VNav after changing the MCP altitude (the PMDG 737 didn't really master the VNav, but plenty of the others don't require this kind of reset).
Use the altitude/speed restrictions on the legs page more for your descent (and STAR), than to get to your cruise altitude.
Also, at 10k you may think that the plane isn't climbing anymore (even if VNav is active) but that's because it has to level off for a higher speed for a while. Give it patience when making that transition.
Thank you very much for your help. I noticed that the aircraft would climb at very high rates, but as long as it was maintaining its speed, and was not posing any damage the its structure, then I'm fine with it 😉 -- Your assistance was highly appreciated. 😂
No problem crosscheck, my pleasure. The PMDG 737 is a little fickle with how it behaves, I've just had a lot of experience with it!
😂
Wow, a reply within 2 minutes, a new record! 😂
hehe -- quickness 😉
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