How Come They Divert Airplanes?

Why not check the No-Fly List before the plane takes off?

Please wait till the aircraft has come to a complete stop

On Tuesday, a flight en route from Milan to Boston was diverted to Bangor, Maine, because it was carrying a passenger whose name appeared on the government’s “No-Fly List.” On May 12, an Air France jetliner bound for Boston also stopped in Bangor to kick off a passenger suspected of being on the No-Fly List. (This was later deemed a case of mistaken identity.) Why can’t the government check passengers against the No-Fly List before the plane takes off?


Because of Department of Homeland Security regulations. When passengers check in for international flights headed to the United States, the carrier does a quick name check. This pre-flight verification typically includes running passenger names against the estimated 30,000 names on the Department of Homeland Security’s No-Fly List. DHS constantly updates and refines the list, but sometimes airlines fall behind. When that happens, misspellings and omissions permit passengers on the No-Fly List to pass through the system.


A DHS department called U.S. Customs and Border Protection provides a second, more thorough check of the passenger list. The airlines are required to send CBP their “manifests”—passenger data that usually include names and birth dates. Since DHS allows the airlines to send this information as late as 15 minutes after take-off, sometimes no-fliers aren’t caught until the plane’s in the air.


Once the manifests come in, CBP’s National Targeting Center in Washington, D.C., checks them against a combined federal law-enforcement database. If CBP finds a match, then the Transportation Security Administration (another Homeland Security offshoot) decides what to do with the “person of interest.” If a passenger is found who is wanted for, say, tax fraud, then the plane would be allowed to continue to its destination. If the suspect is considered more dangerous, then the TSA will order the flight to return to its point of origin or to land at the closest airport. (Bangor is the most common diversion airport for incoming transatlantic flights because it’s the easternmost major airport in the United States.)

The DHS instituted the 15-minute rule after 9/11. It was something of a compromise—the U.S. government gets the information it needs from airlines, and the airlines get their planes off the ground fast. But several highly publicized diversions—most notably, the detention of folksinger Cat Stevens, aka Yusuf Islam—spurred Congress to push for a new system.

Last December’s intelligence reform bill mandated that DHS come up with a new pre-flight screening plan by Feb. 15. However, the agency is still haggling with airlines over new rules that could require manifests to be turned over as early as an hour before the flight. Airlines fret that these earlier deadlines would be a financial burden. But Congress has shown willingness to put up cash for additional safety measures, like reinforced cockpit doors for commercial planes in 2002.

Next question?

Explainer thanks Leah Yoon of the Department of Homeland Security.