KP nospam@please wrote:
Terminal facilities (and maybe centers) split parts of their beacon code
allocation into subsets. The computer is then programmed to perform the
different functions associated with whatever subset a discrete code is in.
For example: In one facility I recall 01XX was used for VFR, 04XX for Local
IFR, and there were a couple others. There were also several sub-subsets
for stuff like VFR w/MSAW or the local traffic/police helicopters.

But, none of this is really important to pilots. Pilots have no way
of knowing how a facility allocates their codes, and even if they
caught onto some patterns over time, the facility is free to change
their internal practices without any notice to pilots.

This originally came up because somebody suggested that a pilot might
determine if they are IFR or VRF based on what kind of code they got
and act accordingly. I think that would be rather foolish.