[Updated] Pings, Pucks, and Traffic on Stratus

December 27, 2013 NOTE: We have a short video (linked here) that shows how to connect ForeFlight Mobile to Stratus, enable the traffic layer, and interact with a traffic target. You can find out more about the ForeFlight Mobile and Stratus integration by clicking here.

April 29, 2013 NOTE: ForeFlight Mobile was updated to show ADS-B traffic data (as of v5.1).  ADS-B Out adoption has grown over the last year, but all of the cautions from this post still apply.  Read on to learn about how the ADS-B traffic system works, and why having ADS-B Out installed in your airplane is critical to getting useful traffic data.


Original post from April 1, 2012:

Many pilots today – in our booth at Sun ‘n Fun and on Facebook and Twitter – have asked about whether or not the Stratus and ForeFlight Mobile support traffic.

Firstly, Stratus does receive the traffic stream. However, ForeFlight Mobile does not to display it (edit: as of version 5.1 it DOES show traffic, see notes above), and here’s why:

You’re flying along and an aircraft passes by. No alert. Another aircraft passes by, no alert. Then another, and another, and another. No alerts. Occasionally, you get an alert. But for the most part, day in and day out, traffic passes by, no alerts. In pretty short order, you lose confidence in your portable ADS-B “traffic” system.

Without certified ADS-B “Out” equipment in your airplane, the narrative above is likely to be your experience if your aircraft is not ADS-B “Out” equipped. ADS-B ground stations only send out traffic information when a properly equipped aircraft “pings” the station. To ping, an aircraft needs certified ADS-B avionics installed that are permitted to ping, receive air-to-air traffic broadcasts, and send traffic information into the national airspace system computers. This ping ability is essentially enabled by what is referred to as “ADS-B Out”.  Stratus is ADS-B In only, and does not provide ADS-B Out capability.

In response to ADS-B Out pings, an ADS-B ground station sends back traffic data in a hockey puck-shaped area centered around the transmitting aircraft. Ground stations aren’t always broadcasting traffic data – they transmit that when an ADS-B Out signal is received.

The “puck” sent is a customized set of traffic data – targets consisting of any aircraft transmitting ADS-B Out, Mode A/S/C, or targets being picked up by radar – observed within a 15nm radius of the ADS-B Out equipped aircraft’s current position (plus or minus 3,500′ in relative altitude).

If your aircraft is not equipped to “ping” you would only receive traffic data centered around other ADS-B Out equipped aircraft that happened to be nearby.  If you are on the fringe of that other aircraft’s puck, you’d be more than half blind.  Since there are few aircraft currently equipped with ADS-B Out, this “blindness” would be a very common situation.

Traffic on a portable ADS-B weather receiver creates a potentially dangerous false sense of security for pilots flying without ADS-B Out. They would not be seeing the whole traffic picture.

As we get closer to 2020, ADS-B out adoption will grow. However, until ADS-B Out adoption is more widespread, ForeFlight Mobile will not be showing traffic data from the system to avoid this situation.