A newly updated FAA draft advisory circular AC 20-151B provides flight departments with fresh guidance necessary in obtaining airworthiness approval for traffic alert collision avoidance systems II (Tcas II), as well as for certification of a stand-alone mode-S transponder system.
“The most significant change associated with the latest iteration of the Tcas II TSO standard, TSO-C119d, is the requirement to incorporate RTCA/DO-300A hybrid surveillance functionality,” according to the AC. This element was specifically added to help reduce congestion on the 1090 MHz frequency.
While the guidance the agency provides in this AC is, of course, not mandatory, the FAA does remind operators, “In [this AC], we describe an acceptable means, though not the only means, to gain airworthiness approval of Tcas II versions 7.0 and 7.1 systems,” said the agency in the draft document. “However, if you use the means described [in the AC], you must follow it in its entirety.” The draft AC also includes guidance for TCAS II versions 7.0 and 7.1, including the 7.1 update that addresses hybrid surveillance functionality. The agency is accepting comments until September 24.