ADS-B and Call Sign Confusion

The ADS-B mandate has arrived, and with it comes the potential for another source of confusion. Most pilots flying with ADS-B systems have a display of traffic in the cockpit, either on a moving map that’s part of a GNSS navigation system or on a tablet like an iPad running an app such as ForeFlight, Garmin Pilot, or FlyQ. These traffic systems usually show the identification of other aircraft, either the registration number or the airline flight number.

ADS-B traffic (TIS-B) as shown in ForeFlight

When ATC issues traffic advisories–for example, “Cessna 1234A, traffic 2 o’clock, 4 miles, a Southwest 737”–it might be tempting to include the target identification in your acknowledgement. For example, “Cessna 1234A, we have Southwest 2345 in sight,” or “Southwest 2345 in sight, Cessna 1234A.”

If that sounds odd, watch some aviation videos on YouTube. At least one pilot flying an airplane with a new glass panel has made a habit of such replies.

For obvious reasons, it’s a bad idea to include another aircraft’s identification or call sign when you respond to ATC. In fact, the FAA’s December 2019 update to AC 90-114 Automatic Dependent Surveillance-Broadcast Operations anticipates this issue:

2.4.3.4 Unless initiated by the controller, pilots should typically not use the call sign or Aircraft Identification (ACID) of observed traffic in radio communications, as this could create confusion for both ATC and pilots monitoring the frequency.

AC 90-114B

So even if you’re equipped with the latest technology, stick to the standard replies when ATC points out traffic:

“Cessna 1234A, traffic 2 o’clock, 4 miles, a Southwest 737.”

“Cessna 1234A, we have the Southwest 737 in sight,” or “Traffic in sight, Cessna 1234A.”

ADS-B Advisory Services: Coverage Essentially Complete in Lower 48

According to the latest maps available from the FAA, the network of ground-based transmitters for ADS-B Broadcast Services (TIS-B and FIS-B) now provides coverage throughout the continental US.

Update: The FAA published a press release on April 14, 2014 announcing the completion of the ground infrastructure, which includes 634 radio stations.

The following diagram shows the locations of the operating transmitters as of late March 2014.

And here’s a diagram that shows the coverage provided by the network. Note that these service volumes assume you are high enough to receive the broadcasts, typically at or above about 1,500 feet AGL, depending on your distance from a transmitter.

Here’s an FAA video that describes ADS-B Broadcast Services.