Inside a cluster of nondescript buildings on a military base in Southern California, 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, monitoring private planes that might be carrying drugs or terrorists.
They don't find many. But they watch everything larger than an eagle that moves in U.S. airspace.
On any given day, 20,000 to 25,000 flights cross U.S. skies. AMOC enforcement agents like Dave Thorn have to decide which blip on the radar screen needs to be checked out.
"This aircraft right here, November-289-kilo-romeo, was coming up from the Antilles, Aruba, in that area, coming into Sugarland, Texas, Houston metro area," Thorn says. "He's crossing our outer ADIZ [air defense identification zone], so I look at him, make sure the registration is good, people on the airplane are good."
These officers investigate nearly a half-million aircraft like this a year. They look for private planes that cross an air defense zone that extends 100 miles offshore. And they look for suspicious aircraft that originate in a border state but don't follow normal flight procedures.
"I was in the Marine Corps for 22 years," Thorn says. "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."
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.
"General aviation is a threat vector that has to be dealt with," says AMOC Executive Director Tony Crowder.
Located inside March Air Reserve Base in Riverside, Calif., 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, twin-engine airplane they tracked from a border state to Chicago in 2010; when it landed, local police got the tail number, and AMOC found out it was Mexican-registered and linked to a narcotics seizure in Atlanta.
"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," says Sullivan. "It was $1.1 million — oddly enough, in Honey Bunches of Oats cereal boxes, which is fun."
Sometimes, Customs won't wait for local law enforcement on the ground; it scrambles its own aircraft to grab the tail number in flight.
Air and marine agents — 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.
"I think it's clear from rational observation that there've been a few events where there was a stronger response than we would have wanted," he says.
A spokesman for the Aircraft Owners and Pilots Association says police encounters at airports have all but stopped since they complained. Crowder confirms AMOC is interdicting fewer private flights these days, with better results — 28 stops so far this fiscal year, leading to 11 arrests, nine of them criminal.
As 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.
"We have taken our technology and we have put it in place in Mexico, and now we are teaching them how to use it," Crowder says.
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