Hi, I'm new to these found and came here searching for help on FMC. I run PMDG 747-400 on an FSX installation and have been trying my hand at configuring the flight plan in the FMCConsider a scenario where I fly IFR and filed a flightplan with the ATC (vatsim or otherwise). The flightplan includes 3 waypoints (among others). The third waypoint has an altitude restriction. The 3 waypoints are close so i realize that I need to start my descent from the first way point to be somewhere in the middle when I cross the second(which has no altitude restriction). Given the fact that the flightplan filed does not contain planned altitude at second waypoint, how do I make sure that ATC will clear me to a specific altitude which I can program into the FMC. I know I'm missing something basic here but I'm new to simming. Please help me! Manav

Manav;You will probably have better luck getting responses if you post in the "747-400" forum...this one is for the LCF.As for your problem, no way to get FSX ATC to issue a specific altitude for a specific point unfortunately. In fact most VNAV descents are disrupted by ATC priorities anyway.

Is it acceptable procedure to request FL change eNroute to conform to the FMC descent profile?Also, can the mods move this thread to the PMDG 747-400 forum? Sorry guys for not realizing this was the incorrect place to post.

The FMC's crossing restrictions that are pre-set into the flight data are those that are directly from valid arrival procedures. These flight procedures are designed to make flight in the terminal areas (close to airports) as easy and efficient for both pilots and controllers, and are often developed with ATC SOPs in mind. As an example, in the case of the SHNON2 arrival, there are crossing restrictions at several of the waypoints. ATC will clear you well enough in advance to meet the first crossing restriction, and then cleared to descend via the arrival. In general, an ARTCC, or Air Route Traffic Control Center ("Center"), will clear you down to the initial altitude on the arrival and will hand you off to an approach sector soon thereafter. At that point, the approach controller will either give you another assigned altitude, or if it is an RNAV arrival and the controller is able, you will be told to descend via the arrival. At that point, you just follow your VNAV profile.You will hear a few different descent instructions:"Descend and maintain..." - meaning descend now. ATC expects that you will move from your current altitude to another, with little delay."Descend pilot's discretion..." - meaning you may vacate that altitude when you see fit (if given a crossing restriction, you must meet that, however: "Descend pilot's discretion to cross HOGGS FL180")."Descend via the ____ arrival." - meaning descend to via RNAV arrival's crossing altitudes.The latter two still allow you room to descend via the computed VNAV profile, though it will not likely be the optimum, idle power, constant-speed descent. In general, you will not need to request an altitude change to meet the VNAV profile, because your descent profile is often faster than what is assumed by ATC (they will clear you down before you hit T/D). On the other hand, saying "Uhm, Center, we're getting close to top of descent" if they haven't cleared you will probably get your radar target stared at with a cocked eyebrow. There's a definite VATSIMism (and understanding between the VATSIM controllers) that the "pilots" rely way too much on the automation, and that the automation can be incorrect if it was set up incorrectly (I've had someone ask for a descent into New York over North Carolina before). I'm not saying ATC never forgets, but if that's your suspicion, it may be better to phrase it in a way that says you're not just blindly following what a computer is telling you: "Center, we'd like lower, if able." If they only give you a few thousand feet, it's because there's traffic ahead of you at a lower altitude that must clear before you may descend, and that was the reason they held off the descent instruction.

Kyle pretty much summed it up. But remember this as well. ATC has their own idea of whats going on that the FMC doesnt. Your FMC will start your descent as if you were going direct from the last fix on your route to the IAP. But if there is traffic, or the approach is on the other side of the runway, you will get vectored off your FMC course. This also means you have more distance to go to get lined up. So if ATC is "late," it's all right. Always listen to the ATC, even if it differs from your FMC.

Only thing I would add to these great answers is that if you are using FSX ATC, yes you CAN request a lower altitude via the ATC window.Of course FSX ATC is also prone to vector you right at a mountain or tell you to descend and then climb again...but I digress :) PS - Kyle, your quote 'though it will not likely be the optimum, idle power, constant-speed descent."...that's what I meant by VNAV being disrupted by ATC, but you said it a lot better.

Thanks guys for the excellent Insights. I'll keep those in mind before I log in for my first vatsim flight. Always ATC first, unless it's the TCAS or ground proximity warning.