Avionics News November 2015 - 11
We are 65 months into this 10-year mandate. During the
past year or two, we are starting to see a significant amount of
movement in this area. The tools available to help owners and
operators of aircraft determine their needs are growing slowly,
but growing nonetheless. The Aircraft Owners and Pilots
Association recently released its ADS-B Out Selector online
tool, which is a nice generic tool for the light general aviation
owner. The FAA has published some good information on its
website. Duncan Aviation has added ADS-B to its Straight Talk
series. And the AEA has developed a website that consolidates
many of these resources into a single, easy-to-use website located at aea.net/NextGen.
Unfortunately, while compliance to the 2020 mandate might
be relatively simple - "just purchase compliant equipment" -
it may not be the best choice. I'd like to investigate ADS-B a
bit closer and possibly help with some of the better questions
you may choose to ask while upgrading your avionics to satisfy the mandate.
ADS-B stands for Automatic Dependent Surveillance-
Broadcast. It is a system that automatically broadcasts your
position independent of the legacy radar system. I would
have suggested it is independent of external input, but as
you will see in a moment, that isn't completely true. So the
basics of the ADS-B system is its ability to know where you
are and broadcast that information on a specific frequency,
hence the 1090 or 978 MHz broadcast requirements.
According to David Loso, manager of avionics sales at Jet
Aviation St. Louis, "All of the major international business jets
already have a DO-260A (previous version) solution available
that will satisfy those areas that have ADS-B requirements in
place currently." He shared his concern regarding non-OEM
ADS-B solutions for newer aircraft. "All newer aircraft are fully
integrated; cockpit displays, FMS, CNS radios, GPS, TCAS,
etc. And these systems are fully controlled by the airframe
original equipment manufacturer and the avionics OEM partner.
Most, if not all, OEM service bulletins are written based on
the aircraft original configuration or configuration modified by
OEM service bulletin or STC." In conclusion, Loso cautioned,
"The operator must take care that the ADS-B solution they consider does not take the aircraft 'out of the family.'"
Whether solving ADS-B Out via an OEM service bulletin,
STC or field approval, there are three fundamental considerations
the owner would be encouraged to evaluate: the ADS-B transmitter; the position source; and, as the title of this article suggests,
The first element of the ADS-B system is the ability to know
where you are in three-dimensional airspace with consistent
and reliable accuracy. The accuracy level of the new system
is at least, if not slightly, more accurate than the current radar
system in the immediate airport environment. The difference
with ADS-B is that the position accuracy is constant along the
entire flight path, whereas with radar, the farther you are from
the radar beacon the less accurate your position is. To achieve
this level of accuracy, the FAA envisioned a performance-based
standard to allow for multiple means of satisfying the position
accuracy without specifying a technology. That sounded reasonable five years ago, and maybe there will be a new technology
on the horizon to satisfy this. But today, nearly everyone is
defaulting to GPS augmented by WAAS meeting the performance of either TSO-C145 or TSO-C146.
The transmitter: 1090 extended squitter or UAT (978 MHz).
From a regulatory perspective, this seems straightforward. If
you fly in Class A airspace, you need the 1090 ES, essentially a
Mode S transponder with extended squitter capability. But what
if you don't fly in Class A airspace? Does the 1090 ES still
make sense? I think yes, or at least a strong maybe.
Talk to your avionics provider; plan
your upgrade; and most important,
schedule your installation.
In addition to the basic airspace requirement, I believe there
are two additional thoughts that should be considered for a
Mode S transponder solution: Do you fly internationally, or are
you required to have a Mode S transponder by the regulations?
While Part 91 (14 CFR 91.215) contains the requirements for
ATC transponder and altitude reporting equipment and use, it
does not mandate a Mode S transponder. On the other hand,
commercial operations under Part 135 (14 CFR 135.143) that
are required to have transponders might require a Mode S transponder unless the system is old (manufactured before Jan. 1,
1990, and installed prior to Jan. 1, 1992), or there is an exemption to the 14 CFR 135.143 mandate.
If you are a commercial operator under Part 135, it may
benefit you to consider either upgrading your existing Mode S
transponder to be ADS-B compliant, if possible, or replacing it
with a compliant version.
While the UAT is an internationally recognized ADS-B frequency, at the present time, the U.S. is the only country that has
committed to using 978 MHz for ADS-B. As a result, there is
no guarantee, and a reasonable likelihood, that the UAT system
will not be compatible with international mandates. Therefore,
if you are likely to fly outside the contiguous U.S., you should
consider an ADS-B solution utilizing 1090 extended squitter
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