Originally Posted by
Bula
Hey guys and gals,
thanks for the reply. The FCOM reference is FCOM 3.03.17 Page 3
SPEEDBRAKES................................................. ......AS RQRD
In OPEN DES :
Use speedbrakes to increase the rate of descent. The pilot may use up to half speedbrakes to maintain the required rate of descent, when engine anti-ice is used.
I thought it may have been a flight control law "g" issue resulting in an altitude overshoot or overspeed, but it seems to only apply with Engine Anti Ice on, and beside you have a .25g increase in pitch authority when speed brake is used. I think most of us have used Full Speed brake with OP DES and EAI without to much of an issue but I wonder if its a pitch attitude and icing issue. In other words, no idea.
Keep trying.. we'll get there sooner or later
Don’t over think it.
I don’t have the same style of page reference as you, however my FCOM has the following in plain English and all it is saying is that you may need some speedbrake to counter the higher flight idle caused by engine anti-ice on.
Originally Posted by PRO-NOR-SOP-17-A-00011544.0001001 / 03 MAR 14
If engine anti-ice is selected in descent, the flight idle is increased. So, to maintain the rate of descent that the airplane had before engine anti-ice selection it may be necessary to use up to half speedbrakes to maintain the required rate of descent, in OPEN DES vertical mode. If the rate of descent has to be increased, full speedbrakes may be used. In DES mode: If the aircraft is on, or below, the flight path and the ATC requires a higher rate of descent, do not use speedbrakes because the rate of descent is dictated by the planned flight path. Thus, the A/THR may increase thrust to compensate for the increase in drag. In this case, use OPEN DES with speedbrakes.