ADS-B is the future of air traffic
control. By utilizing high-integrity signals from
the Global Navigation Satellite System, traffic controllers
can more accurately keep aircraft a safe distance
from one another. This allows for a smaller radius
between aircraft and opens more opportunities for
direct routing and improved procedures in close proximity
of the aircraft during all phases of flight, including
enroute, arrival and departure. The ADS-B system will
replace aging and less accurate radar surveillance
systems around the world, a change which has already
begun.
ADS-B works by converting the aircraft global position
into a unique digital code and combining it with other
data including the type of aircraft, its speed, its
flight number, and whether it is turning, climbing,
or descending. The code containing all of this data
is automatically broadcast from the aircraft’s
ADS-B transmitter or transponder once a second. This
type of transmission has been designated ADS-B “Out”.
ADS-B ground stations up to 200 miles away receive
these broadcasts, and add radar-based targets for
non-ADS-B-equipped aircraft to the mix and send all
of the information back up to equipped aircraft —
this function is called Traffic Information Service-Broadcast
(TIS-B). ADS-B ground stations also send out graphical
weather information from the National Weather Service
and flight information, such as Temporary Flight Restrictions
— this is called Flight Information Service-Broadcast
(FIS-B). Aircraft equipped with the ability to receive
this information are considered to have ADS-B “In”
capability. Pilots can view this information on compatible
traffic display screens or multifunction displays.
Air traffic controllers will see the information on
displays they are already using, so little additional
training will be needed. ADS-B signals are transmitted
once per second, providing a more accurate tracking
system for pilots and controllers.
In US airspace, ADS-B In and Out information is available
on two separate frequency bands:
- 1090 MHz - this is the frequency used by Mode-S
transponders, and when a transponder is equipped
with compliant hardware and software (an ADS-B approved
version of “ES” or “Extended Squitter”),
the transponder itself acts as the ADS-B transceiver
- 978 MHz - sometimes referred to as a “UAT”
(Universal Access Transceiver), is the frequency
reserved for aircraft flying below FL 180; it has
a much higher bandwidth than 1090 MHz (the frequency
is far less congested) and, therefore more data
can be transmitted to the aircraft from the ground.
It is quite easy, for example to have small battery-powered
978 MHz ADS-B transmitters on the ground marking
obstacles, which can then be displayed in the cockpit.
In airspace other than the
US, the 978 MHz frequency is not currently authorized
for use in ADS-B. Due to congestion problems, however,
this restriction may be lifted in the future.
|
