2000: Less than a week after Y2K passes without a global computer meltdown, a glitch in a 1960s computer at the air traffic control center in Washington, D.C., slows and shuts down airlines in the Northeast.

Anybody who has ever listened to an air traffic controller knows they operate like a well-oiled machine, talking at speeds that would make a tobacco auctioneer envious. But the downside to the finely tuned system that directs air traffic across the skies is that even the smallest hiccup can cause nightmarish delays for travelers.

One of those hiccups led to a virtual shutdown of air traffic on the East Coast on January 2000. The problem occurred at what is colloquially known as Washington Center, one of the 20 Air Route Traffic Control Centers that handle aircraft once they have left the immediate airspace around major airports. Washington Center handles flights covering roughly 200,000 square miles of the mid-Atlantic region, including much of the traffic flying south out of New York City.

Normally when a flight is completed or leaves the airspace, the flight plan is deleted. A glitch in the 1960s software that day meant the computer was no longer deleting the flights. As new flight plans came in, the system was overloaded and shut down.

To keep that from happening repeatedly, air traffic controllers couldn’t use their computers to hand off flight plans from one controller to the next. As a workaround, they went old-school and used small strips of paper with the necessary flight information typed out. These slips were then carried from one controller to another by hand.

This sneakernet system works just fine, and is still in existence today as a backup. The problem is that it’s a bit slower to walk a slip of paper across a room than it is to click a mouse.

So instead of handling hundreds of flights per hour, the system grinds to a crawl that ripples throughout the country as delayed flights stack up. On that day, hundreds of flights from Boston, New York, Philadelphia and Washington, D.C., were directly affected, and soon flights around the country experienced related delays.

Interestingly, this air traffic gridlock was apparently unrelated to the fear that had gripped the country just a week earlier. One of the major Y2K fears was that air traffic control computers wouldn’t be able to handle the big 2000. Turns out it wasn’t about the extra two digits, but simply a good old-fashioned software problem. Earlier in that same first week of 2000, a similar kind of computer problem shut down air traffic control in New England.

In the early days of aviation, controlling where airplanes were flying wasn’t a problem. There simply weren’t enough of them in the air, and pilots tended to fly when conditions allowed them to see each other if they should be sharing the same airspace. But by 1926, the United States started to implement rules for air traffic, and by 1930 the first radio-equipped control tower was installed in Cleveland.

By the mid-1930s there were several control towers, and a handful of airlines agreed to start coordinating their flights to and from Chicago, Cleveland and Newark airports. The first air traffic control center was established in Newark by 1936, the same year the federal government took over control of the airway traffic.

Also in the early days, there was no radar to keep track of flights. There wasn’t even direct communication with the aircraft. Instead, controllers simply used a blackboard and maps with small models to estimate the location of airplanes as reported from airports, radio operators along the routes and the airlines themselves.

Numerous control towers and airway radio-reporting centers had been established around the country by the end of World War II. But it was after the war that air traffic control began to resemble what we see today with the implementation of radar. Now air traffic controllers use a combination of radar, satellites and good old-fashioned eyesight to keep track of more than 85,000 flights a day in the United States.

More than $1 billion was spent during the late 1990s to modernize the computers and software used by air traffic controllers around the country. The first of the new systems was installed at Seattle Center in 1998 (pictured above). By the end of 2000, all 20 of the regional centers had received the new equipment.

With GPS and extremely precise radar, air traffic controllers today do a remarkable job of handling dizzying numbers of flights daily. New technologies in recent years have also given pilots the ability to “see” other aircraft from the cockpit.

Future advances using technologies such as ADS-B are part of the next generation of air traffic control system. Adding even more capabilities on the ground and in the air should reduce future aerial gridlock and keep fliers safe.

Source: Various

Photo: Air traffic controllers work the Seattle Air Route Traffic Control Center in 2007.
Jason Paur/Wired.com