Pilot's Guide to Avionics 2014-2015 - 79

2 .

ADS-B Out avionics require the transmission
of a valid Mode S code to operate properly with
ATC 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 .

- 79 -

3 .

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 .

4 .

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 .

5 .

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 ADSB installation . An ADS-B avionics manufacturer can
provide aircraft owners with a list of recommended
service centers to accomplish this work .

2 .

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

Pilot's Guide to Avionics 2014-2015

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