Airspace is split in to different
classifications, each with its own purpose and each with its own rules. There
are seven classes of airspace, lettered A through G. There is no Class F airspace
in the United States, so you will not need to learn about Class F.
In addition to its classification, airspace may be controlled or uncontrolled, towered or non-towered.
Airspace is controlled where air traffic control services are provided. Class A, B, C, D, and
E airspace is controlled.
Airspace is uncontrolled if air traffic control does not exercise
control of aircraft within the airspace area. Class G airspace is uncontrolled.
Towered / Non-Towered
These terms refer to the presence of an operating air traffic control
tower at a particular airport.
Before discussing airspace, it is important to be familiar with general
differences between height references.
MSL: Height above the mean sea level. This is the altitude that
displayed on the altimeter.
: Height above ground level
of maintaining a constant height above mean sea level, the pilots flying above
18,000 feet maintain a constant flight level. In order to maintain a
flight level, pilots set their altimeters to the standard altimeter setting of
29.92. Flight levels are referred to by the first three numbers of the
height to be maintained. For example, if told to maintain FL230, a pilot
would maintain 23,000 feet, with the altimeter set to 29.92.