Avionics News June 2014 - 63

automation and other ADS-B aircraft. Mode S
codes, also known as the ICAO code, are assigned
to an aircraft during registration and then programmed into transponders and ADS-B Out avionics. Mode S codes remain static until a change in
aircraft registration or identification (N-number)
occurs. Portable units require users to input the
Mode S code assigned to each aircraft flown. A
high number of Mode S code entry errors have occurred with this procedure, which prevent proper
target correlation within ATC automation systems
(target drops). Errors have resulted in increased
workload and unnecessary distractions for pilots
and controllers.
Use of portable ADS-B In systems: Use of portable
ADS-B In "receive-only" units is acceptable under the
provisions of 14 CFR §91.21(b)(5) & (c). These units are
limited to listening for ADS-B signals and do not interact
with ATC automation or other ADS-B equipped aircraft.
Users of portable ADS-B In units should be aware that
traffic information broadcasts from TIS-B are initiated
by ADS-B Out aircraft transmitting within a service
volume. Therefore, when an ADS-B service volume does
not detect the presence of ADS-B Out aircraft, users of
receive-only units in the same service volume will not
be provided with transponder-based traffic information
(TIS-B).
Common problems following ADS-B installations:
1. Mode 3/A code processing between transponder
and UAT.
◦ In Dual ADS-B Out systems, the transponder
control panel is typically used to input the
Mode 3/A code, which is then sent to the UAT
for broadcast. When this transfer is not accomplished correctly, a Mode 3/A mismatch
occurs between the transponder and UAT
broadcast, causing ATC conflict alerts.
2.

Non-compatible position source (GPS).
◦ If a position source is used that isn't approved
for use with the ADS-B system, or an approved position source is used but isn't using
the appropriate software version to perform
critical calculations, misleading data can be
transmitted, resulting in a hazardous situation.
Examples include incorrect position, velocity,
integrity and/or accuracy information.

Mode S code programming errors.
◦ The current Mode S code assigned to the aircraft during registration must be programmed
into the ADS-B transmitter at installation. If
equipping with both a 1090 ES and UAT transmitter on the same aircraft, the correct Mode
S code must be entered into both transmitters
and verified. Incorrect Mode S codes will
cause issues within ATC automation. Mode S
code mismatches on dual-Out equipped aircraft
will cause ATC conflict alerts.

Improper SIL/SDA configuration on non-TSO
units (experimental amateur-built and light sport
aircraft).
◦ The installation of non-TSO ADS-B equipment on experimental e-AB and e-LSA
aircraft is allowed but requires the SIL/SDA
parameters to be configured to transmit values
of zero. A SIL and SDA=zero configuration
prevents ADS-B data of unknown quality and
integrity from being processed by ATC automation and other ADS-B In equipped aircraft.

Aircraft with ADS-B Out capable Mode S transponders installed that comply with TSO-C166a
but were misconfigured during installation to transmit as compliant to TSO-C166b.
◦ This problem typically occurs during installation of a UAT Out system on an aircraft with an
existing TSO-C166a compliant Mode S transponder and results in the aircraft transmitting
bad ADS-B Mode S data and good UAT data.

How to avoid problems:
1.

Use a Part 145-certified repair station with appropriate limited ratings to complete and test the
ADS-B installation. An ADS-B avionics manufacturer can provide aircraft owners with a list of
recommended service centers to accomplish this
work.

For ADS-B installations on experimental e-AB and
e-LSA aircraft, use appropriate ramp test equipment to verify system performance. The built-in
test capabilities of individual ADS-B avionics
components are not sufficient to verify proper operational performance of the entire system. q
avionics news

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2014

Avionics News June 2014

Table of Contents for the Digital Edition of Avionics News June 2014