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.

FMI: www.regulations.gov/#!documentDetail;D=FAA-2010-1204-0001, www.faa.gov