Broadcast by ATC to warn air traffic to remain clear of areas
such as open air affairs, forest fires, space launches, crime
scenes, etc. See material on TCA, ARSA and clearances, surface
operation. Each of these areas is sources for deviations from
the FARs and reasons for FAA enforcement actions.
Advisory Circular 91-63B dated 2/28/97 explains how a TFR comes
into being. Nearly any governmental agency can request and obtain
a TFR from the air traffic manager having jurisdiction over the
airspace concerned. The primary objective is safety and NOTAMs
are kept to a minimum in line with this objective. Airspace limits
are usually 2000 and a 3-nautical mile boundary about the
area. Special restrictions apply to aircraft authorized to fly
inside the TRF area. In the Bay Area and California TFRs are most
likely to exist around fires and floods.
Friend of mine was FAA Violated on a non-stop flight from Arizona
to Napa when he over-flew Lemore Naval Air Station at 8500.
There was NOTAM out regarding an air show. It had to stop while
he was in vicinity. It happens.