We're Landing Where? Why Planes Are Diverted to Maine

The headline on May 17 had that same ring to it: "Jet from Italy to Boston diverted to Maine; passenger questioned."

We've heard it before, although it doesn't happen all that often. Despite the fact that tens of thousands of international airline passengers board a small air force of airliners every day and make it all the way to their destination in the United States without delays or diversions, every now and then a "system" of international passenger screening -- a system that clearly needs improvement -- fails.

When that happens, someone who may be listed on the Transportation Security Administration's "no-fly" list of suspected terrorists or potential threats to aviation actually gets airborne on their way to the United States.

The response, when that occurs, is what you hear us reporting about, often as it happens: an airliner diverted and ordered to land, usually at Bangor International Airport in Maine, so the subject passenger can be removed, questioned, and either deported or arrested.

But why do airlines let such "undesirable" passengers on board in the first place?

No Casual Process for the Airline

The answer is a bit more complex than you might think, but it comes down to a balance in economics between the U.S. government and the airlines not wanting to inordinately delay inbound flights, versus the very legitimate security interests of a nation at war.

The problem is that the no-fly list -- a database of names compiled in the United States -- isn't checked against the final passenger manifest of an inbound flight until the doors of the aircraft have been closed and the list is, indeed, final.

That doesn't mean the no-fly list is a mystery before the flight departs. In fact, the international airlines authorized to fly into the United States constantly cooperate with the TSA in using that list to keep from selling tickets to or making reservations for people who may be listed.

For the airline, this is no casual process, because the penalty for failure is the huge cost of having a flight diverted to Bangor, Maine, an expense measured in lost time, lost fuel, missed connections at the destination, and an airliner not available for its next flight assignment, as well as flight crews whose crew duty time may be exceeded and who, therefore, may have to be replaced on the next flight.

The remedy of forcing all loaded, outbound airliners to hold in position at the departure airport with the doors closed while TSA makes its final passenger list comparison has been deemed far too costly, and the airline community has elected to accept the costs of an occasional diversion rather than slow down the flight schedules.

That's why occasionally the screening methods fail and the TSA's final check -- as it did this week -- turns up a name and a birthdate that look suspiciously close to someone on the no-fly list. When that happens, the call on whether or not to order the inbound aircraft diverted to Bangor is made by officials of the Department of Homeland Security -- which now includes the U.S. Citizenship and Immigration Services (formerly known as the Immigration and Naturalization Service).

But Why Bangor?

But why Bangor, Maine, up in the northern woods?

Take a look at a globe with a piece of string in hand. Put one end of the string on Chicago or Los Angeles and the other on Paris (for instance), and stretch it tight. Then look at the path the string creates. If you plotted that same course on a flat paper map, it would appear to be a giant arc instead of a straight line, and that's because what you're looking at is called a "great circle" route -- the shortest distance between two points on a curved surface.

You can also see that the string enters the United States fairly close to Maine, and thus the first and best airport (because of its remoteness for anyone wanting to harm a major American city) to use for a security diversion is Bangor.

And Bangor International Airport is not only geographically well-suited to such diversions, it's been the diversion point of choice for decades for everything from medical emergencies to passenger rage incidents. Bangor has FBI agents living nearby, customs and immigrations offices well-staffed and at the ready 24/7, and airport management has learned to make a cottage industry of getting diverted airliners back in the air quickly. So that part of the "system" works well.

What we've got to improve is the quality of the computer screening of the passenger list before an airliner leaves its gate at a foreign field.

John J. Nance, ABC News' aviation analyst, is a veteran 13,000-flight-hour airline captain, a former U.S. Air Force pilot and a lieutenant colonel in the Air Force Reserves. He is also a New York Times best-selling author of 17 books, a licensed attorney, a professional speaker, and a founding board member of the National Patient Safety Foundation. A native Texan, he now lives in Tacoma, Wash.