Pilot's Guide to Avionics 2014-2015 - 76

ADS-B INSTALLATIONS
Continued from page 75

transmitter on an amateur-built aircraft with
an experimental airworthiness certificate . The
FAA, however, strongly discourages the use
of uncertified ADS-B Out equipment even in
experimental aircraft . Uncertified equipment,
including uncertified 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

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be able to provide safe separation between one
aircraft and other traffic in the vicinity . The FAA and
international partners conducted a safety 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 77 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 .
Pilot's Guide to Avionics 2014-2015

Table of Contents for the Digital Edition of Pilot's Guide to Avionics 2014-2015
