FAA plans follow-on to Alaskan ADS-B project

 - May 22, 2008, 5:56 AM

Buoyed by the success of its three-year ADS-B (automatic dependent surveillance-broadcast) operational evaluation project, named Capstone and centered on Bethel in western Alaska, the FAA plans next year to increase the number of participants and to implement a second, broadly similar project centered on Juneau, Alaska.

ADS-B, which is expected to play a key role in the future Free Flight era, is sometimes described as the next-generation transponder technology. This is because individual aircraft carry avionics units that transmit GPS position, altitude and intent once a second over a dedicated datalink, instead of being periodically interrogated by ground-based secondary radars, as is the case today.

Bethel was chosen as the initial project area because of its remoteness from mainstream and itinerant traffic flows, thereby achieving a Free Flight-like environment for local participants, most of whom remain within about 200 mi of the airport. The ADS-B transmissions are received by all other ADS-B-equipped aircraft within reception range (typically out to 100 nm) and the pilots of each aircraft can then see the relative positions, ranges and bearings, tracks, groundspeeds and idents of all other aircraft in their vicinity. Also, the transmissions are received by unmanned ground stations, which retransmit each aircraft’s downlinked data back to distant ARTCCs, and also uplink weather, notams, pireps and other data to the participating aircraft.

At Bethel, around 150 single- and twin-engined airplanes, ranging from Cessna 180s, 207s and Beavers to Shorts 330 Skyvans and Twin Otters, carry FAA-provided ADS-B installations, which consist of the basic transponder, datalink unit and associated GPS receiver, along with a cockpit display of traffic information (CDTI). The package also includes a digitized, color moving map of the project area, driven by GPS, that also identifies dangerous terrain at or below flight altitude ahead in bright red.

FAA officials note that while Alaska has more controlled flight into terrain (CFIT) accidents than in any of the other 49 states, there have been none in the Capstone area since the project was launched 18 months ago. Next year 50 more aircraft will be added to the program.

ADS-B operations at Juneau are expected to begin next summer. Currently, avionics suppliers have submitted bids to the FAA covering equipment, as well as installation, certification and service support, and a contract award is expected early next year. As in the Bethel experiment, the FAA will cover these costs for participants over the Juneau project’s three-year duration, after which the operators will own the equipment.

Initially, the FAA had not planned to extend its Capstone ADS-B program beyond Bethel, but commercial, state and federal officials in Alaska quickly realized the systems’ potential safety benefits. “As soon as we saw the reduction in CFIT and other problems with the ADS-B-equipped airplanes,” said one FAA observer, “we had to develop the case for expanding the program, and then find the money to do it.”

But simply enlarging the area around Bethel, while still limiting it to the original, primarily air taxi, user community was unlikely to yield new evaluation data or funding, despite the attendant operational safety benefits to more aircraft over an expanded area. As a result, Juneau was chosen to provide a more challenging mix of air taxis and higher-performance aircraft.

The Juneau program, which will run concurrently with the Bethel operation, could involve 100 to 150 airplanes including de Havilland Dash 8s and Boeing 737s.