The Air Traffic Control System Command Center owns all controlled
airsapce in the US. They allocate authority to 21 ATC Centers via letters
of authorization (LOA) that specify the lateral and vertical boundaries of
each
center's airspace. The centers divide their airspace up into high alititude
and low altitude areas with each sub-divided into multiple sectors. The
laterial
and vertical boundaries of each sector are designed to handle the particular
geographical area and traffic flows.

Centers delegate authority to the approach / departure radar facilities
(TRACONs)
within their airspace via letters of authorization that define the lateral
and vertical
boundaries of the TRACON's airspace. There are 197 TRACONs in the US as of
the last time I checked.

TRACONs in turn grant airspace autority via LOA to the tower facilities
within
their airspace. Again, laterial and vertical boundaries are defined in the
LOA.

Handoffs occur when a flight crosses a boundary between facilities or
sectors.
None of the charts show all these boundaries. Sectionals show controlled
airspace
associated with an airport terminal area, but there usually multiple sectors
within a
large TRACON. Low altitude IFR En Route charts show the center boundaries,
but not the sector boundaries. Frequencies as charted for the various
sectors in a
general area, but these are not always the frequencies that a flight will be
given during
a handoff. Instrument flights deal with this by simply following the
instructions
given by ATC; eg. "N54321 contact Memphis Center on 134.25." We don't
concern our selves about where the boundaries are, because we will be
prompted
during the hand-off. Also, you may be given a hand-off before or after you
cross
an ATC boundary, depending on controller work load, his ability to
coordinate with
the receiving controller, and aircraft speed.

Should you miss a hand-off or get out of range before a hand-off occurs,
simply find
a center frequency or TRACON frequency within range and call to re-establish
communication. If you are not on the correct frequency, the controller will
get you
to the correct one.



"Mxsmanic" wrote in message
...
What determines the boundaries between airspace managed by an en-route
ATC center and an approach or departure center? I don't see any clear
indication of which is which on sectionals. There are boxes saying
who to contact for approach, but nothing that shows where the handoffs
between terminal control and center usually occur. Is there a general
rule?

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