With more aircraft equipped with ADS-B, NASA’s Aviation Safety Reporting System (ASRS) is starting to receive more pilot comments on specific instances where ADS-B In played a role in collision avoidance.
For example, ADS-B provided situational awareness to a Cessna 172 pilot with respect to unannounced traffic at a non-towered airport. The pilots estimated the other aircraft, which was not talking on frequency, passed nearly overhead and about 200 feet above them. “Had we not seen him [on ADS-B], I believe he would have hit us,” the pilot wrote in the ASRS report.
A Cessna 182 pilot in IMC observed a conflicting aircraft on the onboard traffic advisory and alert system. Although ATC said the threat aircraft (a Cessna CitationJet) was going to pass well clear, the pilot said the ADS-B display indicated “maneuvering was required.” Upon landing, downloaded ADS-B data from both aircraft showed that although the Citation began a descent, it “briefly leveled off at 10,000 feet (our altitude). This happened just as they were passing our location.”
However, many ADS-B targets were displayed while one pilot transitioned Class C airspace in VMC, making it harder to discern threats. The absence of any traffic advisory resulted in a false sense of security “when an aircraft came directly head-on and passed underneath me probably 100 to 200 feet…ADS-B wasn’t too helpful there, because I was right over the airport and there were a lot of targets on the ground and in the air, so it was hard to make any sense of the traffic scope with the targets overlapping.”