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-sized 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.
"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.
"It's a pretty new phenomenon," said Andrew S. Gordon, of the general counsel's office at the Department of Homeland Security.
A Democratic congresswoman from Arizona, Gabrielle Giffords, proposed last month to close that loophole with an Ultralight Smuggling Prevention Act. Giffords called ultralights "the latest threat to border security."
Giffords said the Customs and Border Protection's Air and Marine Operation Center in Riverside, Calif., detected "193 suspected incursions and 135 confirmed incursions by ultralights from Oct. 1, 2009 through April 15th of this year."
Arizona has become a gateway for Mexican marijuana. Last year, law enforcement agents seized about 545 metric tons of marijuana in the Tucson sector, which has a 262-mile border with Mexico, more than all other sectors combined.
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.
Ultralights have fabric wings attached to aluminum tubing. Small two-stroke engines that 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)."
When Mexican smugglers began using small airplanes in the 1980s and 1990s, the U.S. government responded by deploying six Aerostat surveillance blimps to strategic border locations, thwarting air smuggling for many years.
But the Aerostats, tethered by 15,000-foot cables, return to their ground pads at night to avoid snaring legal aircraft that might get entangled in the cables.
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.
Giffords said some of the smugglers' aircraft have been detected "flying up to 200 miles into our country from Mexico."
Both humanitarian concerns and legal considerations prevent law enforcement from firing on the ultralights when they spot them.
"There are rules on deadly force," Gordon said, noting that the ultralight pilots wouldn't survive a strafing. "If you shoot them, you're going to kill them."
Such legal considerations give the traffickers leeway.
"They don't care about flying with their lights on. They don't care about flying at the proper designated altitudes for aircraft. They don't care about flying through controlled air spaces," Pearson said.
H.L. Cooper, a flight instructor for ultralights in the Tucson area, said he's regularly approached by people whom he presumes are smugglers.
"The first thing out of their mouth is, 'How much weight can it carry?'" Cooper said.
Drug gangs in Mexico care little about pilot training.
"They are getting some 'gofer' out there to jump on these things, and then it's, 'Hasta la vista, baby,'" Cooper said.
The vehicles are usually overloaded, making them unstable. "If you hit some turbulence, the aircraft can start to break apart," he said.
In one of the earliest known incidents of the use of ultralights for drug smuggling, Jesus Isaias Iriarte, a 25-year-old pilot carrying 210 pounds of marijuana, crashed in a field north of Tucson in October 2008. After a plea deal, he was sentenced to 33 months in federal prison.
Under the toughened measures in Rep. Giffords' proposal, smugglers could be given sentences of up to 20 years and $250,000 fines.
Iriarte's attorney, Charles Slack-Mendez, said it's not difficult for cartels to recruit flyers from Mexican beach resorts, where ultralights are common.
"My understanding is that they are not all that difficult to drive. It's not much more difficult than a motorcycle," he said.
Pearson, the sheriff's sergeant, said traffickers might not stop at smuggling marijuana. They will also bring cocaine and heroin — or explosives.
"Here's my big concern," Pearson said. "Four hundred pounds of C-4 (plastic explosive) will do a heck of a lot of damage. If that were a light airplane, or if that were a 757 talking to someone, I bet the Air Force would shoot them down."
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