In a lot of our company approach briefings, there is mention of sticking to standard approach speeds. i.e. 220 at the IAF, 180 on base/final approach track and 160 from 8nm -4nm, I have not been able to find any reference to where these speeds have come from other than they seem to fall within the range of speeds depicted in the Pan Ops Doc 8168 Vol 1, Table I-4-1-2 for various parts of the approach.
In regards to the FMC the default speed that comes up for the decent which is 240/100, from reading up on it, the FMC takes the airport restriction speed but with minus 10 knots, what is the reason for deducting 10 knots off it?
Thanks in advance