Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Aviation Communication & Surveillance Systems (ACSS) traffic alert and collision avoidance system (TCAS) units installed on but not limited to various transport and small airplanes. That NPRM proposed to require upgrading software. That NPRM was prompted by 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. This action revises that NPRM by proposing to require new updated software for certain TCAS units. We are proposing this supplemental NPRM to correct the unsafe condition on these products. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.