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Guest cat3208

FMC descent problems

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Guest cat3208

I am currently flying both the PMDG 737 & 747 and I always overshoot my descent profile. I enter the wind in the forecast page, apply drag when prompted by the FMC and reset MCP altitude to the FAF altitude. I do not fly with the FS9 ATC so I do not initiate the descent before or after the T/D prompt. Any help would be appreciated.Mike Gadman

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You didn't mention if you're using VNAV or controlling descent with the MCP. An example of a specific case would also have been helpful.My experience with VNAV is that it is sufficent for descents down to FL180, but most of the time I use the MCP to control my IAS and VS. One thing that surprises some is the VS at high altitudes, which can reach 3000 fpm. The rate will decrease as you get lower and into thicker air, where your groundspeeds for a given IAS decrease.One helpful rule of thumb is to divide your altitude by 3 to get the TOD. For example, at FL300 you'd start your descent 100 miles out. This works too for when you are descending through FL180 you should be about 60 miles out, and at 40 miles out when you get handed over to a terminal control sector you'd like to be lower than 13000 (the STARS usually have an altitude constraint at the arrival gate of something between 10,000 - 14,000. There's variations here, at KATL you're turning downwind abeam the airport at 12,000.The VNAV will automatically set up a descent profile that you can use for reference even if you are using the MCP.


Dan Downs KCRP

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Guest cat3208

Dan, I use VNAV for the entire descent profile.

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