Avionics News March 2017 - 30
IS YOUR NEW ADS-B EQUIPMENT WORKING CORRECTLY?
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Many aircraft owners contemplating an
ADS-B Out equipment installation to comply
with the 2020 mandate may wonder what's
in it for them.
"The positioning data provided by ADS-B
is more precise and timely than radar, and
there is no doubt that this increases safety,"
said James Marks, who leads the FAA's
ADS-B Focus Team.
For example, the accuracy of radar is
affected by the distance and atmospheric
conditions between the aircraft and the
radar site. At the outer limits of radar's
range, the accuracy of radar positioning can
be skewed by more than 1,000 feet. Radar
positioning depends on the sweep rate for
each site, which can be between four to
six seconds in terminal areas. This isn't the
case with ADS-B because the avionics on
board the aircraft determine its precise location using GPS, and report its position once
a second to a network of more than 600
ground radio stations that feed air traffic
control facilities across the country.
ADS-B also provides coverage in some
areas where there is no radar capability,
such as mountain valleys and over the Gulf
of Mexico beyond the reach of shore-based
radar. When controllers can track aircraft
with ADS-B, they can provide the same services as when an aircraft is in radar contact.
Aircraft owners and pilots who opt for
optional and enhanced ADS-B In equipage
will enjoy the additional benefits of subscription-free traffic and weather information displayed with TIS-B and FIS-B. But to
receive TIS-B traffic information in the cockpit, aircraft must properly transmit ADS-B
Out data. That's because the FAA ground
system needs the aircraft's ADS-B reported
position to determine what relevant traffic
information should be broadcast to it. q
PAPR service to validate your ADS-B avionics' performance.
Repair shop technicians must be careful during ADS-B installations
(which are often done at the same time as an aircraft's 24-month altimeter
system and altitude reporting tests) and ground tests to properly shield
transponder antennas. Improper testing can create false targets on the
traffic displays of air traffic controllers and nearby aircraft.
The FAA has seen an increasing number of reports about ADS-B
and transponder ground tests resulting in test signals being sent into
surrounding airspace. This could prompt controllers to rapidly direct traffic
around false targets or require pilots to react to resolution advisories issued
by TCAS equipment or to ADS-B In traffic alerts.
The recent increase in improper ground tests has prompted the FAA's
ADS-B Focus Team to publish a Safety Alert for Operators to emphasize
the importance of following applicable transponder and ADS-B testing
procedures. For more on this, visit www.faa.gov/other_visit/aviation_
Aside from antenna-shielding issues, the FAA says other high-priority
ADS-B installation issues relate to improperly entered codes, including:
* An aircraft's FAA-assigned ICAO 24-bit code is wrong. Some
ADS-B units are manufactured with a default code. If it isn't
changed to the assigned aircraft code at installation or is entered
incorrectly, the aircraft will not be properly recognized by the
FAA's ADS-B ground system. If an aircraft's N number can't
be connected to a particular flight, a PAPR request cannot be
* Two different ICAO codes might be loaded in error into the Mode
S transponder and the UAT on the same aircraft.
* The flight identification number should match the aircraft call sign
used in air traffic control communications and the aircraft call sign
filed on your flight plan.
If the transmitted ICAO code doesn't correlate to your aircraft's
assigned N number, your ADS-B installation is not compliant with the
FAA rule. Ground test equipment will only verify that an ICAO code is
loaded, not that it is valid for your airframe.
Having different codes in your Mode S transponder and your UAT
will appear on a controller's display as two aircraft in close proximity. If
your aircraft is equipped with ADS-B In, you may see a second aircraft
displayed very close to your own position, prompting you to try to avoid
an aircraft that isn't there. Mistakenly thinking you need to act fast to
avoid a collision with an aircraft that doesn't exist can cause a safety
The FAA ADS-B Focus Team's highest communications priority is to
quickly contact any aircraft operator with incorrect ICAO codes (either a
single erroneous code or two codes that don't match) or the wrong flight
identification number. The agency handles about 200 of these high-priority
cases a month.
Because ADS-B performance problems can emerge after initial installaContinued on page 32