Stephen Pope

The chaos that erupted on the morning of September 11 brought a flood of questions. Where were these airplanes coming from? Who was flying them? Why were they crashing into skyscrapers? In short, what on earth was happening? For hours there was no official word from&nbsp; Washington. Through a spokeswoman, the White House told the nation the President had been hurried onto Air Force One, which was in the sky headed for an “undisclosed location.”
Soon key details of the attacks started to emerge. Anchors on the major cable networks announced the flight numbers of all the aircraft involved, along with the aircraft types, departure airports and scheduled destinations. 
Remarkably, the networks even had the radar-based flight paths of the airliners, and were showing the exact routes the airplanes had taken. It was a quartet of eerie loops that left no doubt about the precise moments the hijackers had taken control of each airplane.
How was it that the major television networks were all able to relay such information so soon after the terrorist attacks? 
Shortly after the crashes, officials at several Web sites, including one called FlightExplorer.com, brought up the FAA-derived aircraft situation data (ASD) for all the airplanes involved and put the flights through software filters. When it was clear that these indeed were the aircraft involved in unleashing the mayhem, the Web sites sent the information to the TV networks, so that not only did the networks have the basic flight information, they were also able to show the world the precise paths of each of the ill-fated jetliners. 
“If we had to wait for an official NTSB report, I think it’s safe to say it would have taken months to get this information,” one anchor told viewers as the flight-tracking feed played on the screen, only hours after the attacks on the World Trade Center and the Pentagon. 
Viewing the flight paths each of the airplanes took is a chilling experience. American Airlines Flight 11, a Boeing 767, the one that had crashed into the North Tower, was shown climbing out of Boston Logan International Airport and heading to the west on a Great Circle route toward Los Angeles. Its flight number, altitude, groundspeed, type and ETA were all included in a data tag next to a small aircraft-shaped blip. Then, suddenly, the airliner could be seen making an abrupt 130-deg left turn and heading down the Hudson River, directly for its target. 
Meanwhile, United Airlines Flight 175, also a 767, also out of Boston Logan, made a gradual turn to the south, but headed out over New Jersey and circled back to approach Manhattan from the opposite direction, over the Statue of Liberty, before crashing into the South Tower 21 min after the first airplane had hit the North Tower. The third jet, American Airlines Flight 77, a Boeing 757, flew toward LAX as far as eastern Kentucky before turning back toward the capital and crashing into the Pentagon. 
The fourth airliner, United Flight 93–the 757 that crashed in Pennsylvania–made it to Cleveland before turning back toward the southeast. Its track showed something strange, however: instead of flying to a city and crashing like the other airplanes had, the radar track showed a slight meandering, and then the blip disappeared from the screen. There were erroneous reports for a brief period that the airplane had crashed at Camp David, the Presidential retreat in western Maryland. We now know the heroic efforts of a group of passengers may have saved the White House or the Capitol.
With a graphic picture of the exact flight paths of the aircraft involved in the worst terrorist attack in U.S. history, the overwhelming confusion that otherwise would have been experienced by a dismayed nation was at least diluted slightly. Suddenly, the country could see where these rogue airplanes had come from and how they had arrived at their ultimate targets. A small but important part of the mystery had been solved.
Flight-tracking providers such as Flight Explorer came into being in 1995 after the FAA opened its ASD data stream to private companies. Before then only the airlines had access to the feed from the DOT’s Volpe Center in Cambridge, Mass., which they used to keep track of their own fleets. Since then, many of the services have been enhanced and expanded, and today many Web sites offer free tracking of all airline flights.
Also included in the feed are all Part 91 aircraft operating on IFR flight plans. Security concerns prompted NBAA and corporate operators in 1997 to lobby the DOT for a way of blocking tail numbers from the system as some operators became worried about the security of their passengers. Flight-tracking providers soon voluntarily agreed to block the tail numbers of aircraft operators who did not wish to be included in the ASD data stream. As a result, NBAA now acts as a clearinghouse to coordinate the tail-number blocking program.