Im thinking some may be unaware of flight idle vs ground idle? :-)http://imageshack.us...control8wx.jpg/

We are speaking of the approach idle that creates problems with some.The FMC is aware that all its calculations will be made for flight idle, eventually corrected for approach idle if antiice is selected in the des. forecast, however, also without winds, FMC is unable to give the right path to mantain speed at idle.The problem maybe not the FMC but the idle itself. Wrong values/thrust.You can see from the scheme you posted that N2 is wat the idle controls, and in approach we must have 72-79% but in the NGX seems to be slower. N1 (wich make most of thrust) is too high and provide to much thrust expecially with AI on.So, if the FMC is unable to do a descent in ideal conditions (but with AI on and programmed in FMC) there is definetly something wrong with idle or FMC.

:(

MattDid I quote you? Or did I answer maybe a question (maybe this PO was Highjacked) from Steffen? So my answer was right for Steffen Thx Ian

We are speaking of the approach idle that creates problems with some.The FMC is aware that all its calculations will be made for flight idle, eventually corrected for approach idle if antiice is selected in the des. forecast, however, also without winds, FMC is unable to give the right path to mantain speed at idle.The problem maybe not the FMC but the idle itself. Wrong values/thrust.You can see from the scheme you posted that N2 is wat the idle controls, and in approach we must have 72-79% but in the NGX seems to be slower. N1 (wich make most of thrust) is too high and provide to much thrust expecially with AI on.So, if the FMC is unable to do a descent in ideal conditions (but with AI on and programmed in FMC) there is definetly something wrong with idle or FMC.

I just ran a flight and used LNAV/VNAV the entire flight and the only problem I found was that the FMC descent page computed a descent speed of 330kts even though the cruise speed computed at 290kts. I changed the DSC speed to 290 and it flew the profile perfectly, so I wonder if that may be others problem.

The idle issue is related to some users and with AI usage.With some configurations the idle changes from flight to approach at 15500ft, this giving more thrust and making almost impossible to mantain speed in VNAV.This is for some users. I had this thing happen with hot fix 4.Now I don't have problems until using anti ice that (as it must do) increase the idle.However, also if you let the FMC knows about it, the aircraft path is not ideal for speed management and speed brakes are needed.I don't know if it is the same for other users, but as shown in the video there is also a random problem of idle not restoring after AI disengagement.I assure you that the route is correct, it could be flown without any DRAG REQUIRED if no antiice is used, also if using ASE and no forecasts are inserted.So, the problem is the AI on my system, the idle (or also the AI) on others

Just finished another flight with overall real conditions. It was a short 700MN hop from PAJN to CYYJ. Everything went well except I had to bring the speedbrakes out for some time under 10.000ft cause my external weather engine injected new weather which was a bit conterary to the one before. That caused a bit too much speed than allowed but we were down early enough to configure the plane correctlyfor the ILS.The idle worked well this time, 43% at the beginning of descent to arround 32% shortly before capturing the LOC.

I just ran a flight and used LNAV/VNAV the entire flight and the only problem I found was that the FMC descent page computed a descent speed of 330kts even though the cruise speed computed at 290kts. I changed the DSC speed to 290 and it flew the profile perfectly, so I wonder if that may be others problem.

I think there is a mix here of this idle bug sticking to high N1 (I personally have experienced this once where I used engine anti ice on the ground at the departing airport) and those who may not be used to descending with such a slippery airplane. I personally have done EVERY descent in my NGX (around 150-200 flight hours) on VNAV, at least down to below 5K. I always descend at 279-290 kts, and I have no issues with slowing the thing down. I rarely use forecast, and I only ever had to go around from being too fast the first one or two flights, which is expected from transitioning from heavies.I do agree, there will be times you will need to take over descent, but the FMC is there to compute the most economical descent- I like to let it do that. Every pilot has their flying style, and everyone will do something differently.As a side note, my idle bug seemed to happen when the NGX got stuck thinking the AI was still on- probably needs to be addressed in a fix or the next SP. To kick it back in line, I had to enable the throttle override for a minute or so in order for me to advance and then re-idle the hardware throttle. That seemed to at least do the trick for me.