Going Mainstream - GPS Declassified: From Smart Bombs to Smartphones - page 128

coastlines of the continental United States, the Great Lakes, Puerto Rico, the
U.S. Virgin Islands, portions of Alaska and Hawaii, and much of the Missis-
sippi River basin. 40
Approving GPS for Aviation
The faa began phasing in gps use in June 1993, six months before the ioc
declaration. 41 Pilots could immediately use approved gps equipment as their
primary en route navigation method for domestic and oceanic routes, but its
use with landings came with restrictions. At first pilots could use gps only for
nonprecision approaches—instrument landings that use ground-based radio
signals to align the plane with the runway but do not provide vertical guidance,
which remains visual. By contrast, landings with reduced visibility require pre-
cision approaches, where ground equipment transmits both lateral and verti-
cal guidance. Airports use a variety of navigation aids, and some lack instrument
landing systems that can provide vertical guidance. The initial faa phase- in
opened five thousand gps approaches at 2,500 U.S. airports. 42
Formal faa approval of gps for civil aviation followed on February 17, 1994,
and the next month the agency published the first certified gps approaches— a
process that would take years to cover all affected airports. 43 Published
approaches originally filled thick paper manuals, but with the advent of digital
circuitry they were programmed into cockpit instruments, including gps receiv-
ers. Until the faa certified a particular runaway approach for gps, pilots had
to follow the traditional approach and actively monitor existing ground-based
navigation aids unless the plane was equipped with gps instruments featuring
Receiver Autonomous Integrity Monitoring (raim) or an equivalent method
of detecting faulty satellite signals. 44 raim circuitry and software enables receiv-
ers to verify the accuracy of a position derived from four satellites by compar-
ing it to signals from a fifth or sixth additional satellite. 45 Despite the
requirement for backup systems, faa officials left no doubt that gps was the
direction for the future. At the time, faa administrator David Hinson remarked
that he saw no reason gps would not become the only navigation system. 46
Hinson's comment reflected a widely held view: the arrival of gps repre-
sented enormous potential cost savings for the general aviation sector, airlines,
airports, and the overburdened faa-managed air traffic control system. Some
seven hundred thousand general aviation pilots operating two hundred thou-
sand aircraft looked forward to the greater affordability of panel-mounted gps
receivers costing $2,000 to $5,000 that would eventually replace $20,000