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tomtom989898

FMC VS Autopilot off in decent?

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First off, probably, well yes the best add on aircraft I have ever purchased!

 

I have a weird issue and it is more than likely something I am not doing right, but I seem to have an issue when I start the descent with autopilot in vnav mode, everything seems to go great until I am about 13,000 feet.  For some reason I find the 777 is always 4 to 5 k higher that the desired height I need to be at.  Have seen this time and time again for some reason. 

 

It will clearly show in the FMC flight level 2700 at next VOR, but when it reaches it, I am still at 7,000, of course causing me to go around again, but wanted to know if you have seen this or am I doing something wrong?  I try not to cut auto pilot until 1000 to go.

 

Notes :FSX, windows 7 64 bit, active sky, pfpx flight plans.

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Maybe your throttle is left open while AT is in HOLD mode (during descend normally)? 

Maybe unplanned tailwind is an issue, or unplanned anti ice usage?

Maybe you requested unreasonable steep profile?

 

 

What profile diamond shows? is it centered (on profile)? have you got "drag required" message at CDU scratchpad?


[color=#a9a9a9][size=1][size=4][img]http://forum.avsim.net/public/style_images/flags/rs.png[/img][/size] Lj. Prodanovic[/size][/color]

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Also did you enter the winds into the descent forecast page?  Plus nothing wrong with using the other tools, every descent I am using VNAV, FLCH, & V/S


Rob Prest

 

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thanks for the reply, the throotle seems to be fine and I try to keep vnav and lnav active until 1500.  I have not seen a drag required on most landings, only a few when I had a huge tailwind, which I did deploy some slats.

 

I will get back with you on the profile, I am new to the aircraft, so not sure where that is at this point.

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The point about the throttle is that on the 777X if you don't retard your hardware throttle to idle during descent that can mean N1 might not be able to go to idle, which could reduce your descent rate. That might be a bigger problem below 13000 ft because the aircraft has to decelerate to 240 knots before 10000 ft. If it can't slow down properly due to excess thrust it won't be able to maintain the vertical profile.


ki9cAAb.jpg

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You can try setting the FMC descent speed to a higher speed to steepen the vertical profile.


Rem Yang
Flying is Fun!
 

Boeing777_Banner_Pilot.jpg

fs2crew777.jpg

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The point about the throttle is that on the 777X if you don't retard your hardware throttle to idle during descent that can mean N1 might not be able to go to idle, which could reduce your descent rate. That might be a bigger problem below 13000 ft because the aircraft has to decelerate to 240 knots before 10000 ft. If it can't slow down properly due to excess thrust it won't be able to maintain the vertical profile.

 

I bet that may be the problem, I usually cut it, but not to idle.  Let me try this!  Thanks!

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