Plane & Pilot
Tuesday, August 3, 2010

Beyond Today’s Transponder

Demystifying ADS-B

Two doors down from our hangar is another Skylane with an older IFR GPS that may not work as an ADS-B position source. Since the owner doesn’t fly outside the U.S., a better option for him will be to get a 978 MHz UAT with a built-in “blind” (no display or database) GPS, which will be cheaper than replacing the unit in his panel. If he wants to get traffic and weather, he’ll need to add some sort of display. Since TIS-B and FIS-B are advisory-only, it should be possible to use an electronic flight bag or other portable display, or he can spend more money for a multifunction display in the panel. He’ll need to keep his existing Mode C transponder, and there may be some installation issues involved in coupling it to his UAT (they’re required to use the same barometric pressure source for altitude and a common control for the squawk code).

On the other side of our hangar is an RV-8 homebuilt that’s flown only VFR and rarely in Class B or C airspace. Its owner can probably get by with just a Mode C transponder. He’ll need permission from ATC for entry to Class B or C (or E above 10,000 MSL) airspace.

Across the field, a bizjet operator who wants to take full advantage of the system will replace his Mode C transponder with 1090ES Mode S; but instead of using ADS-R and TIS-B for situational awareness, he’ll probably upgrade his existing traffic alert and collision avoidance system (TCAS) to a version that combines actively detected transponder traffic with ADS-B in. Avidyne has announced exactly that option for its TAS-600/610/620 series devices. For that, he’ll need dual (top and bottom) antennas (the rest of us can get by with a single bottom-mount antenna).

None of this will be cheap. The FAA estimates that equipping the roughly 160,000 aircraft in the general aviation fleet for ADS-B out will cost at least
$1.2 billion, which works out to $7,500 per aircraft. I expect to spend less than that, since I already have a compatible GPS, but others may find they’ll need to spend more.

What will we get for that money? An air traffic control system that’s more reliable, offers better coverage at low altitude (ITT’s John Kefaliotis, a former air traffic controller who heads the effort to build ground stations told me he’s installing them at many general aviation airports—35 so far—to provide a usable signal all the way to the ground), plus advisory traffic and weather for those who install a receiver and display. And it might not have to be our money! Several industry representatives interviewed for this story pointed out that there’s precedent for the federal government subsidizing purchases of equipment that’s required for the ATC infrastructure, whether ground or aircraft based. My current plan is to wait for my existing transponder to fail—but I could be persuaded to equip more quickly if someone made it worth my while. Stay tuned!

For More Information
Accord Technology
(NexNav Min GPS SBAS receiver/sensor)

(TAS-600/610/620 enhanced for ADS-B)

FAA Final Rule Requiring ADS-B In

Free Flight Systems
(RANGR 978 MHz datalink family)

(GTX-330 Mode S transponder, GDL-90UAT)

(ADS-B ground stations and value-added services)

(Portable and remote-mount UAT devices)

Trig Avionics
(Mode S transponders withADS-B support)

University Of North Dakota
(Survey on future NextGen in-cockpit weather products)


Add Comment