Keeping Watch On America's Vertical Borders Tens of thousands of private planes fly through U.S. airspace daily. Federal agents at a Southern California air base monitor those flights, looking for drugs or terrorists. Sometimes, they find them.

Keeping Watch On America's Vertical Borders

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Inside a cluster of nondescript buildings on a military base in Southern California, federal agents sit in front of screens day and night, monitoring private planes that might be carrying drugs or terrorists. They don't find many. But they watch everything that moves in U.S. airspace that's larger than an eagle. NPR's John Burnett took a rare tour of the facility and he sent this report.

JOHN BURNETT, BYLINE: The big radar room at the Air and Marine Operations Center looks vaguely like NASA Mission Control. Thirty-two federal agents sit at Dell PCs, each one watching a different region of the country. On any given day, there are 20,000 to 25,000 flights in U.S. airspace. Detection enforcement agent Dave Thorn has to decide which blip on his radar screen needs to be checked out.

DAVE THORN: This aircraft right here, November-289-kilo-romeo, was coming up from the Antilles, Aruba and that area and coming into Sugarland, Texas, which is in the Houston metropolitan area. He's crossing our outer radars so I look at him, make sure registration's good, people on the airplane are good.

BURNETT: These officers investigate nearly half a million aircraft like this a year. They look for private planes that cross an air-defense zone that extends a hundred miles offshore. And they look for suspicious aircraft that originate in a border state, but don't follow normal flight procedures. Again Dave Thorne...

THORN: Well, I was in the Marine Corps for 22 years. I was an air traffic controller. This mission of watching for our borders and stuff, I believe in it. I think it's a righteous thing to be doing.

BURNETT: Though most people don't know the program exists, U.S. Customs has had a center like this to keep an eye out for drug planes crossing the southern border for 26 years. In the age of terrorism, they watch the skies for everything. Because private aviation is essentially unregulated, pilots don't have to file flight plans or talk to a tower. Tony Crowder is executive director of AMOC, as it's called.

TONY CROWDER: General aviation is a threat vector that has to be dealt with.

BURNETT: Located inside March Air Reserve Base in Riverside, California, AMOC is a division of Customs and Border Protection. But its agents don't wear green uniforms and chase immigrants through the brush like drone pilots. These air security officers go to work with a computer mouse and a headset. Though they dress in service boots and khakis and strap on a .40-caliber handgun, they rarely leave the base.

When they identify a suspicious plane, they notify local police to take action on the ground. Intelligence research specialist Heather Sullivan remembers the big two-engine plane they tracked from a border state to Chicago in 2010. When it landed, local police got the tail number and AMOC found out that it was Mexican-registered and linked to a narcotics bust in Atlanta.

HEATHER SULLIVAN: They ended up doing a stop due to a large number of bags being placed in a taxi cab and heading back to the plane. It was $1.1 million in, oddly enough, Honey Bunches of Oats cereal boxes, which is fun.


BURNETT: Sometimes, Customs won't wait for local law enforcement on the ground. They scramble their own aircraft to grab the tail number in flight.

UNIDENTIFIED MAN: Charlie, got your radar contact - Angels 9.50443. Good sidetrack - safe flight.

BURNETT: Air and marine agents - yes, they track boats, too - are aggressive. Earlier this year, private airplane owners complained publicly that gun-toting local and state police, excited by a hot tip from AMOC, were confronting bewildered law-abiding pilots at general aviation airports. Crowder acknowledges changes were necessary.

CROWDER: I think it's clear from just rational observation that there have been a few events where there was a stronger response than we would have wanted.

BURNETT: A spokesman for the Aircraft Owners and Pilots Association says police encounters at airports have all but stopped since they complained. Crowder confirms AMOC in interdicting fewer private flights these days with better results - 28 stops so far this fiscal year, which led to 11 arrests, nine of them criminal.

As the AMOC begins its second quarter-century, its composite picture of North American airspace is nearly complete. Its computers take in radar from the FAA, Department of Defense, Canada and, most recently, the country where many of the illegal drugs originate.

CROWDER: We have taken our technology and we have put it in place in Mexico. And now we are teaching them how to use it.

BURNETT: The new radar technology will allow Mexican federal police and military to better track drug planes in their own airspace and share the information with the Air and Marine Operations Center in Southern California. John Burnett, NPR News.[POST-BROADCAST CLARIFICATION: The audio version of this story, as did a previous Web version, says that general aviation is "essentially unregulated." While there is American airspace where a private pilot is not required to file a flight plan or be in contact with a control tower, as we reported, that is an incomplete depiction of noncommercial flight. There are strict rules governing private aircraft that cross the U.S. Air Defense Identification Zone, which encircles the nation's borders. They must file flight plans, register the flight and be in contact with air traffic control. Moreover, general aviation pilots and aircraft must comply with numerous Federal Aviation Administration regulations and certification requirements, according to the Aircraft Owners and Pilots Association.]

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