But a critical step remained: a demonstration that proved ADS-B would actually work under real conditions. The FAA had to sign off on the test, a process hampered by red tape strung by mid-level bureaucrats. The solution came amid severe weather, not in Alaska but in the nation’s capital.
On September 19, 2000, Washington, D.C., braced for Hurricane Gordon, and non-essential federal workers were told to stay home. It was just what Hallinan needed. “Most of the [FAA] building was gone and I was able to have meaningful conversations with decision-makers without having a lot of front guard to body-block me,” he says. Those discussions ultimately cleared the way for the FAA to approve Skip Nelson’s history-making test flight of ADS-B in January 2001.
In the years that followed, Capstone added the Wide Area Augmentation System (WAAS) to correct errors in GPS signals introduced by disturbances in the ionosphere and timing errors caused by variations in the orbits of satellites. With WAAS, position updates appeared on the flat-panel displays in cockpits and on controllers’ screens with up to five times the accuracy previously possible. Vertical precision was good enough to set up IFR approaches for landing at airports without controllers or radar-supplied glideslopes. And, if the ground-based transceivers failed for any reason, instruments onboard aircraft were receiving ADS-B data from each other, allowing pilots to maintain a safe distance.
Capstone reshaped a culture, just as its technology is about to change air traffic control in and outside of Alaska. When funding for Capstone ended in 2005 with less than two-thirds of the state covered by ADS-B, the FAA turned the effort into a national program with the Surveillance Broadcast Services Office, part of the George W. Bush administration’s NextGen program. The ultimate goal of NextGen is to use ADS-B as a replacement for radar. Hundreds of ground-based transceivers have already been installed across the United States, providing ADS-B coverage on the east, west, and Gulf coasts, as well as along much of the border with Canada.
By 2020, an advanced version of Capstone’s ADS-B will be the backbone of national airspace management in the United States. When the program is fully operational, all airplanes flying in the country will be required to have ADS-B avionics, which will provide what the FAA expects will be unprecedented traffic awareness and up-to-date weather information. If NextGen performs as well as Capstone, air travel in the United States should become more efficient, with more direct routes and shorter separations between aircraft during flight. The result is improved safety and efficiencies that the FAA expects will translate into hundreds of millions of dollars in annual savings.
The FAA was “looking for a solution for the future,” says Robert Lewis, the current Anchorage-based FAA regional administrator. “When they learned how successful our efforts were up here, they began to see that this might be the answer they were looking for.” Ironically, Alaskan pilots will not benefit from NextGen’s version of ADS-B, if they fly the many passes and canyons where ground stations have not—or cannot—be installed. The mountains still cut the line-of-sight communications between ground transmitters and aircraft, just as the horizon will terminate ADS-B transmissions to transoceanic pilots.
A space-based version of ADS-B, developed by Skip Nelson’s new company, ADS-B Technologies, overcomes the problem by using Globalstar satellites to relay signals between aircraft and ground stations. Over some of the harshest terrain in Alaska, pilots are testing this version of ADS-B for Nelson’s company, and I’m invited along for one of the tests.
For the first test of the year, Nelson is at the controls, and I am in the copilot seat. Our twin-engine Piper Navajo Chieftain lifts off from Anchorage’s Merrill Field, flies down Cook Inlet, then banks toward the mountains. Over the next hour and a half, we fly between 300 and 500 feet above the ice pack and open water, below the line of sight of ground-based ADS-B transmitters.
Blinking green lights on the ADS-B Link Augmentation System (ALAS), mounted on a table behind my seat, verify that a Globalstar in low Earth orbit is relaying our ADS-B signal to ground stations, and that we are receiving signals from those stations as well. The signals complete this circuit within 400 milliseconds, with the electronics inside the ALAS box interpreting and sending them to the multifunction display in the Chieftain’s cockpit, which indicates our position within 50 feet of actual.