below 18,000 feet can choose either 1090ES
or 978 UAT. Most other countries are using
the 1090ES standard, so aircraft owners
traveling internationally will want to equip
with 1090ES. 978 UAT will be attractive to
some owners since it can display free
weather data in the cockpit.
How did we get two ADS-B standards?
978 UAT is technically a superior system
since it has a faster megabit per second
data transfer rate that can accommodate up
to 500 aircraft simultaneously. However,
the airlines weren’t particularly interested
in free weather and preferred a system
compatible with other countries.
There may also have been concerns
that if all U.S. aircraft were equipped with
1090ES, this lower bandwidth system
could become saturated in large metropolitan areas with many aircraft. Having a
separate 978 UAT alternative offloads aircraft from the 1090ES standard by offering
a carrot to users in the form of free
If you’re uninterested in ADS-B
because it’s unavailable in your area, check
out the ADS-B coverage map. By the end
of September, ADS-B coverage is planned
for the entire east and west coasts and a
number of northern states. At that time,
the FAA also plans to achieve In-Service
Decision (ISD), which certifies ADS-B as
safe, secure, and ready for nationwide
Finally, if you think the ADS-B mandate
means you can get rid of your transponder,
think again. Transponders are still needed
so that airliner TCAS can locate other aircraft, and they’re considered essential to
the FAA’s backup plan in case ADS-B or
GPS fails. They’re also needed to transmit
ADS-B data for 1090ES.
ADS-B is not just another box you need
to add to your aircraft. Instead, think of
it as a system. In some cases, you may
already have some or all of the system
components needed to comply, which
could save you money.
For ADS-B Out capability, you need a
position source and a transmitter. A 1090ES
This coverage map shows the fifteen regional zones (in
green) where ADS-B service is scheduled to be available in
the United States by the end of September 2010.