Systems Covered By The Proposed AD Manufactured By
L-3 Subsidiary ACSS
A software glitch in some Aviation Communications &
Surveillance Systems (ACSS) TCAS units has prompted the FAA to
issue an NPRM for an AD on the units. The FAA published the NPRM in
the Federal Register Monday.
The agency is proposing to adopt a new AD for various aircraft
equipped with certain ACSS TCAS units. This proposed AD would
require upgrading software. This proposed AD results from reports
of anomalies with TCAS units during a flight test over a high
density airport. The TCAS units dropped several reduced
surveillance aircraft tracks because of interference limiting. The
AD is proposed in an effort to prevent TCAS units from dropping
tracks, which could compromise separation of air traffic and lead
to subsequent mid-air collisions.
The FAA says the NPRM is the result of reports of anomalies with
the Aviation Communication & Surveillance Systems (ACSS)
Traffic Alert and Collision Avoidance System (TCAS) units during a
flight test over a high density airport. The TCAS units dropped
several reduced surveillance aircraft tracks because of
interference limiting. When the TCAS unit interrogated aircraft in
a high density airport area, some of the targets disappeared from
the cockpit display or were not recognized. One occurrence of
dropped tracks occurred for 30 to 40 seconds of a 90 minute flight
segment. This condition, if not corrected, could lead to possible
loss of separation of air traffic and possible mid-air
collision.
ACSS TCAS Control Unit
After evaluation of all relevant information and determined the
unsafe condition described previously is likely to exist or develop
in other products of these same type designs. This proposed AD
would require accomplishing the actions specified in the service
information described previously.
The deadline for comments is February 11, 2011. The compliance
period for the AD is 48 months from issuance.
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