ASRS Pilot Reports Relay ADS-B Pros and Cons

 - November 25, 2019, 9:49 AM

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.”


While ADS-B traffic is useful information, the overall system design leaves much to be desired. In my plane, the traffic display is like a ground radar scope and is so totally decluttered as to hide any contextual information, such as whether targets are on final approach to a given runway. And while target information is also displayed on maps and charts, those targets are often hard to see against the background. The avionics vendor could address those issues, if they wanted to. And there is no guidance on how to avoid ADS-B targets, especially if they have a closing vertical separation. Then there's the matter that there is no guidance on ATC communications regarding ADS-B targets other than experience. In short, ADS-B traffic displays have been thrown over the proverbial fence for pilots to figure out on their own how to use them.

I have been directing the ADS-B traffic info to my phone running the iFly app. I have found it useful to set the range to 5 or 10 miles to minimize distractive clutter and improve resolution in crowded airspace. One is lucky to visually acquire a target beyond 2 miles anyway. The iFly app uses the user chosen chart as the background, adding contextual cues: "There's someone over the West edge of the lake over there, heading North, 200 feet below." Wx info needs to be viewed on the other end of the scale, looking regional. The two types of data are delivered together, but are really incompatible.

The point of the article is quite valid however, this new capability has been just tossed to us to figure out how to make use of it. The downside is to spend too much attention directed at displays in the cockpit and not enough looking outside, where the danger really is. Perhaps this would be another good application for augmented reality, with the data presented in a natural manner outside. This would have the additional benefit of eliminating sight-line blocking structure.

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