T/D and Cruise Descend

[Guest georg]

Hello,I am usually doing cruise descend with PMDG NG airplanes meaning that I initiate "descend now" 20-50 nm before T/D point. By manuals the system should then descend with 1000 fpm that is okay. But then after passing T/D it should automatically notice that if I for example have set to cross an intersection 10000 feet below that is only 20 miles ahead of me, it should increase the VS dramatically to arrive at the set altitude on corresponding point. But mine just keeps descending 1000 fpm and only way to get down is using VS mode. Is this now a bug or am I doing something completely wrong?Thanks.

[mburkhard 23]

>But then after passing T/D it should>automatically notice thatGeorg,no it shouldn't. The plane will continue to descend at 1000fpm until reaching the descent profile. Keep in mind that if you initiate a descent with DES NOW you are flying BELOW the calculated descent path for some time depending on how early you start your descent. If you do use DES NOW your T/D point becomes irrelevant, the FMS is then just looking for the descent path.On the ND you have a visualisation of your descent path and it shows how much you are below or above. Normal VNAV Path descent is resumed once that diamond symbol reaches the middle of the scale, then you know you are right on your descent profile.That being said it usually doesn't make much sense to use DES NOW unless the controller tells you to descend before you have reached your T/D point.I hope I was able to help...Best regards,Markus

[Guest Hetzenauer2]

Hello Georg,first of all, the "descent now" option in real life is used only when advised to descend by ATC immediately, because the fuel consumption will increase.When advised to, the A/C will initiate that descent with about 1000fpm, as you stated. Now it

[Guest georg]

Thanks for this great help guys! Seems logical and I was aware about it before as well, but the main question for me is that why it doesn't recalculate the descend path and keeps descendindg with 1000 fpm when I soon have to be 10000ft below.

[Guest venquessa]

A side note... quite often on approach on VATSim I get given descent instructions like "Descend at will, be at 15,000 or below by Midthrust, 10,000 by Ockham and hold unless instructed otherwise. If these are in the FMC legs I would FIRST hit decend now, if your planned crossing of either is higher than ATC has given you and then enter the alt restrictions and see if VNAV will fly it.The catch is when MID is not on the plan. I usually decend manually, although I'm sure a fix based on "abeam MID" could be inserted into the FMC... can't it?