Originally Posted by
David1991
So in Order to set the Target Speed.. which Vref Shall i Look to.. the one on the pfd or the one on the Fmc... theY differed Recently... that s why i am asking
The glib answer is to use the ‘book’ value, the AFM is the basis of certification. Thus what is the basis of the FMS speed, computation, integrity level; or the basis of EFIS; where do the values come from.
Without knowledge of your aircraft, if the EFIS Vref display is automatic and associated with low speed awareness and stall (amber / red bands), normally based on AoA (certification basis), then this should be the more accurate (less susceptible to error) because AoA does not depend on wt. Alternatively is this the manual set speed via the FGC.
The FMS could use AoA, but from the discussion so far appears not, because the interface with wt.