In the early hours of September 1, 1983, Korean Air Lines Flight 007 was nearing the end of a flight from Anchorage to Seoul when a Soviet Air Force fighter shot it down over the Sea of Japan, killing all 269 people aboard. The Boeing 747 had drifted off its assigned route and spent more than two hours inside Soviet airspace before it was hit. Investigators working under the International Civil Aviation Organization found no equipment failure at all: the crew, ICAO concluded, failed to notice that the autopilot had either been left in a simple heading-hold mode after takeoff, or had been switched over to the aircraft's inertial navigation system only after the plane had already flown beyond the range at which that system could capture its intended track. Either way, the autopilot flew a fixed compass bearing instead of the computed course the crew believed it was following, and nobody on the flight deck caught the difference.
Two weeks later the White House answered with a promise about a different kind of error. On September 16, deputy press secretary Larry Speakes told reporters that President Reagan had decided to make the Global Positioning System, a network of military satellites already under development to tell any receiver its own location, available to civilian airliners once the system became operational, expected in 1988. What the announcement offered the rest of the world, eventually, was a way to know, independently of a chart or a compass, where you actually were.
When GPS reached civilian hands, it did not tell the whole truth. The Defense Department had built a feature into the broadcast signal called Selective Availability: a deliberately corrupted timing error that held civilian accuracy to within about 100 meters, while a separate, more precise signal went to receivers holding the military's own key. The system opened to civilians, in part, to answer a disaster caused by nobody checking which mode was actually flying the plane, now shipped the public a second, engineered source of uncertainty, built in on purpose and switched on by default.
On May 1, 2000, President Bill Clinton ordered Selective Availability turned off at midnight, ending the deliberate error in the signal civilians received. The change showed up within a day: a National Geodetic Survey ground station in Erlanger, Kentucky, recorded its scatter of positions shrink from a 45-meter radius to 6.3 meters once the switch flipped, at no cost to the system but a policy decision. With Selective Availability zeroed, the administration's own fact sheet said, a disabled car's GPS signal could finally show which side of a divided highway it was on, instead of only the general stretch of road.
In September 2007 the government announced that the next generation of satellites, GPS III, would be built without any capacity for Selective Availability at all. The 2000 order became permanent not because a future president promised to leave the switch alone, but because the hardware to bring it back would no longer exist. A feature once built to reserve full accuracy for one customer and ration a known error to everyone else was designed out of the system's own future.
The satellites had never lied. For years, by policy, the version reaching the public was made to.