The FAA has issued a safety notice to advise pilots of the continued high number of TCAS alerts that started when flying approaches to Runway 16L/16R at Denver International Airport (KDEN) after an airport improvement project ended in 2004. The agency said TCAS II alerting algorithms are not designed to account for certain ATC separation standards, particularly visual and parallel approaches at high-elevation airports.
In June 2019, Denver Tracon implemented a 1,000-foot vertical offset during simultaneous operations to Runways 16L/16R to reduce the risk of collision if an aircraft overshoots the final approach course. While the number of resolution advisories (RAs) between converging aircraft has decreased, the overall rate remains at a comparable level because of an increase in RAs for aircraft once on the final approach course. Approximately 17 percent of operations select traffic advisory (TA)-only mode while converging to the final approach and about 20 percent of aircraft on approach switched to TA-only mode after receiving an RA.
These findings indicate to the FAA that there is a heightened risk of a midair collision because flight crews may be desensitized by nuisance RAs on final approach at KDEN. The agency said pilots should reevaluate their operating procedures in a TCAS II mixed-mode environment to consider loss of collision avoidance guidance with TCAS II in TA-only mode and the implications of TCAS II not returning to TA/RA mode during a missed approach/go-around.