It was just a rumor, but I liked the idea. I'd heard that the FAA was going to equip all the airplanes in the Washington, D.C., area with ADS-B and UAT so it could better monitor their movements. The rumor got legs from the unfortunate, apparently inadvertent, incursion by the Cessna 150 into the Washington ADIZ that resulted in the mad scramble that played repeatedly on the national news.
But I liked the sound of the rumor. I recently equipped my Cessna Cardinal with the Garmin GDL90 ADS-B (Automatic Dependent Surveillance-Broadcast) UAT (Universal Access Transceiver), so, although it's self-serving, I'm in favor of anything that will promote the implementation of ADS-B. For the moment, the coverage area is pretty limited unless you're flying along the East Coast or a couple of isolated locations around the country. So I liked the rumor. But, unfortunately, it appears it's just a rumor.
The advantage of ADS-B to pilots is that equipped airplanes offer air-to-air as well as ground-to-air traffic information. The data available in the cockpit includes the target's unique ID and ICAO identifier, the relative altitude (or barometric altitude) of the target and whether it's climbing or descending. (There are actually two data links that are assigned to ADS-B: 1090 MHz Extended Squitter [1090 ES] for aircraft that typically operate at or above 18,000 feet; and the UAT [978 MHz] for aircraft that primarily operate below FL180.)
As good as it is, there's a major disadvantage to ADS-B. Well, not to ADS-B per se, but to the lack of availability of ground-based transceivers (GBTs). In order to display non-ADS-B-equipped airplanes on a cockpit display of traffic (CDTI), the host airplane has to be within line-of-sight of a GBT that sends up traffic forwarded from ground-based air traffic surveillance sensors, typically radar. The uplink of non-ADS-B traffic is referred to as Traffic Information Service-Broadcast (TIS-B). Because the uplinked radar information is not as accurate as the ADS-B targets, the icon on the cockpit display for "degraded" non-ADS-B traffic looks a bit like a Pacman that's had a bite taken out of its backside; the ADS-B traffic is displayed as a chevron or arrow head pointing in its direction of movement.
In my installation, the traffic and weather are displayed on an MX20 multifunction display. A series of options are available on the MX20 to control the display. The ADS-B traffic, but not the TIS-B radar targets, can show a trend vector that indicates where the target will be in one to 10 minutes (selectable by the pilot). The ADS-B targets also display their unique ID. The UAT system does provide a VFR "privacy" mode for pilots who don't want to receive air traffic services and don't want their ID broadcast to the world. Other airplanes will still see their target but it will be flagged as "VFR."
With the dedicated traffic page displayed I have the option of zooming in or out, or "selecting" any particular target. When a target is selected, its icon changes from blue to green and a data block in the upper right hand corner of the screen shows the target's relative position to my airplane and my position relative to the target, the target's speed, distance from me and its relative altitude. (I can also elect to have the traffic information superimposed on the sectional-style map.) If I haven't opted for traffic to be displayed and a target becomes a potential threat, the MX20 flashes a "TRAF" alert warning me to call up the traffic page.
I can also select a "text" page that lists all the targets within the selected range of the display in order of their distance from my airplane. In addition to the distance, the text lists: host/target relative positions, speed, altitude and for ADS-B targets whether they are small, medium or heavy.
The first chance I got to exercise the ADS-B in my airplane was during a flight from upstate New York to Danville, Virginia. At 8,000 feet, I began to pick up targets near Harrisburg, Pennsylvania, and stayed within sight of GBTs for the rest of the flight.
Whenever a controller called traffic for me, I had already been aware of it from the display. With all traffic selected and the map scale set at a range of 100 miles the map was covered with blue targets. I scaled back down to 20 miles and narrowed the "protected" airspace to 2,000 feet above and below my altitude.
At one point, I saw an airplane on the display at my 12 o'clock position coming straight toward me. According to the target's data block the airplane was 900 feet above me. I waited for the controller to call the traffic. When he didn't, I did.
"There's traffic at my 12 o'clock and two miles, 900 feet above me."
"What's your problem?"
"No problem, just wanted to let you know I have the traffic."
"He's a thousand feet above you; that's legal separation!"
True, it was never a threat, but it was still nice to know it was there.
