Avionics News June 2014 - 60

ADS-B INSTALLATIONS
Continued from page 59

transmitters, should not be installed on any
aircraft with a standard airworthiness certificate.
Uncertified ADS-B transmitters do not comply with
14 CFR 91.227 and will not be permitted to operate
in airspace requiring ADS-B starting in 2020.
Air traffic control does not use data from these
uncertified transmitters, which prevents controllers
from providing flight following services or
separation services to aircraft that are so equipped.
Data from uncertified transmitters are not displayed
on certified ADS-B In displays, and pilots in aircraft
with certified ADS-B equipment will not be able to
see aircraft equipped with uncertified transmitters.
Can an aircraft owner or avionics shop
install an uncertified GPS as an ADS-B
position source?
Aircraft owners or avionics shops may install
an uncertified GPS on amateur-built aircraft and
light sport aircraft with experimental airworthiness
certificates. Uncertified equipment, including
uncertified GPS units, should not be installed on
aircraft with standard airworthiness certificates.
These position sources do not comply with 14
CFR 91.227 and will not be permitted to operate in
airspace requiring ADS-B starting in 2020.
As with uncertified transmitters, uncertified GPS
integrated into an ADS-B system will transmit
data that cannot be used by ATC or other certified
ADS-B In systems. Contact the manufacturer
to learn which GPS systems are approved for a
particular ADS-B system.
What are the risks of using an
uncertified position source?
The risk with any GPS receiver, when used to
support separation services, is the potential for
position measurement error without detection.
If the position error is too great, ATC would not
be able to provide safe separation between one
aircraft and other traffic in the vicinity. The FAA
and international partners conducted a safety

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2014

analysis prior to publishing the ADS-B final rule
to define the error detection boundary, and ADS-B
performance requirements are based on this
analysis.
Certified GPS sensors compare GPS satellite
measurements against each other. When a
satellite signal error becomes great enough to
detect, the receiver will reject that signal. The
integrity performance specified in the ADS-B
rule depends on the proper operation of this error
detection feature that ensures the safety of using
ADS-B position based on GPS measurements.
Navigation Integrity Category specifies an integrity
containment radius around an aircraft's reported
position, as defined in TSO-C166b and TSO-C154c
14 CFR 91.227. The NIC radius (bubble around
aircraft) must be 0.2 nautical miles.
By comparison, uncertified commercial-grade
GPS sensors assume the system is working properly
and do not attempt to detect errors in satellite
measurements. When presented with an erroneous
measurement, these GPS sensors will calculate
an erroneous position. FAA safety analysis found
this to be unsafe. Therefore, ADS-B position
information based on these sensors is prohibited
from being used to support air traffic separation
services and ADS-B air-to-air operations.
What equipment is available?
Approved avionics are available from multiple
manufacturers. The list on page 61 is current as of
April 2014. Check with the avionics manufacturer
for the latest updates on which GPS position
solutions can be matched with a particular ADS-B
unit.
Several manufacturers have products in
development that will be available to meet the
2020 mandate for ADS-B Out. Some approved GPS
receivers are also certified GPS navigators. They
may be installed to support precision approaches in
addition to providing ADS-B position information.
In some cases, the GPS receiver may be integrated
with a multifunction display providing a moving
map, an ADS-B traffic display, access to the FIS-B
information and more.
Avionics News June 2014

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