SONOYTA, Mexico — Several times a week, drug smugglers somewhere along Mexico's border with the United States strap themselves into low-flying ultralight aircraft and take off with loads of marijuana.
They usually fly at night with no lights and often they're guided only by the dim screen of a handheld satellite navigation tool, looking for a precise spot in the desert.
The smugglers generally don't land. They've modified the ultralight aircraft with drop baskets that can hold 150 to 250 pounds of marijuana wrapped in brick-size units and covered in plastic. They move a lever, and the bricks fall to the desert for ground crews to pick up and smuggle onward across the country.
It's a perilous tactic, and pilots can break limbs or die in crashes.
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"It's a fairly risky endeavor for them to try to do this.... They do fly close to the ground, which can be dangerous because of power lines," said Steve Cribby, a spokesman for the Department of Homeland Security.
Ultralight aircraft evolved out of hang gliders, and the Federal Aviation Administration doesn't classify them as "aircraft." That legal loophole allows dopers to bring in sizable loads of marijuana and get lighter jail terms than if they'd used a car or small airplane.
On May 16, the North American Aerospace Defense Command scrambled two F-16 jet fighters to intercept an ultralight aircraft crossing into Arizona and followed it for about 30 minutes before it flew back into Mexico.
Humanitarian concerns and legal considerations prevent law enforcement from firing on the ultralights when they spot them.
Ultralights have fabric wings attached to aluminum tubing. Small two-stroke engines, which sound much like a whining lawn mower, power rear propellers. The pilots sit in sling seats that give the vehicles the appearance of winged tricycles.
"I hate to say it, but those things are very stealthy aircraft," said Sgt. Rick Pearson of the air support unit in the Sheriff's Office of Pima County, Ariz. "They don't have much of a reflective character (to catch radar signals)."
To avoid ground-based radar at night, the ultralights generally fly low, tracing routes over illuminated highways, although authorities have tracked them flying at altitudes of 12,000 feet.