Originally Posted by
k.swiss
Hello All Question:
Descending with OP DES and green-dot-speed gives a very shallow ROD, (less than 700FPM with a standard weight) try and use speed-brake and the VLS shoots up, even worse on 321.
Instructor once told me better to use V/S if you want to get down faster when at green-dot-speed but in some cases if selecting for example -2,000FPM at green-dot the speed trend starts to creep up.
Question 1:
When in this situation of high V/S selected and speed trend is shooting up why am I told speed-brake is useless in V/S mode? Surely if the speed is shooting up because of the high ROD speed-brake will have some effect.
Question 2:
What is the true meaning of "speed" mode on FMA when in V/S, it keeps the ROD but how much is the speed trend allowed to fluctuate?
VS mode priorities VS over IAS
1. If you select a high VS, the speed brakes won’t change your descent rate. They’ll just keep the speed in check if it’s still accelerating at idle.
2. Speed mode does just that, but is limited by what the engines can give you. If your VS is too high to maintain at idle thrust, it’ll simply accelerate. Take a look at the mode reversions.