The visiting British pilots were training near a naval air station one night this month when their helicopter came within about 150 feet of an ultralight plane flying without lights. The ultralight darted away toward Mexico without a trace.
The near-disaster over the Southern California desert was an example of drug smugglers using low-flying aircraft that look like motorized hang gliders to circumvent new fences along the U.S. border with Mexico. The planes, which began appearing in Arizona three years ago, are now turning up in remote parts of California and New Mexico.
And in a new twist, the planes rarely touch the ground. Pilots simply pull levers that drop aluminum bins filled with about 200 pounds of marijuana for drivers who are waiting on the ground with blinking lights or glow-sticks. Within a few minutes, the pilots are back in Mexico.
"It's like dropping a bomb from an aircraft," said Jeffrey Calhoon, chief of the Border Patrol's El Centro sector, which stretches through alfalfa farms, desert scrub and sand dunes in southeast California.
The Border Patrol has erected hundreds of miles of fences and vehicle barriers along the border and added thousands of new agents, so drug smugglers are going over, under and around.
As U.S. authorities tighten their noose on land, ultralights are another tack to smuggle marijuana. The Customs and Border Protection agency counted 228 incursions along the Mexican border in fiscal 2010, up from 118 a year earlier, when it began keeping track. There have been 71 since the start of fiscal 2011 on Oct 1.
The agency counts an incursion when authorities seize an aircraft or nearby drugs, when a trained source spots an aircraft that is correlated by radar, or when enough people see an aircraft to establish a cross-border flight pattern.
Tunnels are another means to circumvent tightened border security. Lined with rail tracks, lighting and ventilation, two were discovered in San Diego in November that netted a combined 50 tons of marijuana on both sides of the border. U.S. authorities found 71 clandestine tunnels since October 2008, more than during the previous six years.
Smugglers also use single-engine wooden boats to ferry bales of marijuana up the Pacific Coast. U.S. authorities seized 47 tons of narcotics off of Southern California shores since October 2008, including 740 pounds this month in an abandoned craft at Dana Point, about 75 miles north of the border.
Under Federal Aviation Administration regulations, ultralights weigh less than 254 pounds, carry just five gallons of fuel and fly at a top speed of 63 mph. They are not designed to carry anything other than a pilot. No pilot's license or certificate is needed, though regulations advise that the aircraft should not be flown over populated areas or in the dark.
But drug pilots often zip along at night just above power lines.
Kevin Kelly of U.S. Immigration and Customs Enforcement was with about a dozen agents looking for ultralights under a full November moon in the desert east of Nogales, Ariz., when he heard what sounded like lawnmower in the sky. The aircraft appeared from the south.
"It's got this big, long wingspan _ it's almost like Batman," said Kelly, ICE's assistant special agent in charge of investigations in Nogales. "It's almost like a glider with a little guy underneath it piloting it."
Kelly watched the ultralight throttle back, get close to the ground and dump bundles packed in duct tape. The pilot picked up speed and wheeled back toward Mexico.
The agents waited for someone to pick up the load _ 286 pounds of marijuana _ but no one came.
Ultralights initially flew as far north as the Phoenix area but they now generally stay within 30 miles of the border, said Matt Allen, special agent in charge of investigations for ICE in Arizona. Their small fuel tanks require pilots who fly far north to either refuel or take apart the aircraft and truck it back to Mexico.
Pilot Jesus Iriarte was arrested in October 2008 after landing an ultralight with 222 pounds of marijuana strapped to the frame in Marana, Ariz. _ nearly 100 miles north of the border _ and was sentenced to prison.
"Gone are the days when they could come deep into the U.S. undetected," Allen said. "They really don't want to be on the ground anymore. They're dropping it and flying away ... It makes them less vulnerable."
Authorities are having more success capturing drivers who pick up the drugs.
Last month, Border Patrol agents arrested Sergio Favela near Douglas, Ariz., as he was allegedly loading 220 pounds of pot into his pickup truck around 3 a.m. A complaint filed in federal court in Arizona says Favela, a U.S. citizen who was captured after a short foot chase, told authorities he was to be paid $1,500.
Heightened enforcement in Arizona appears to be pushing smugglers to California and New Mexico, some authorities say. In California, authorities have confirmed 30 ultralight incursions since December in Imperial County, a remote farming region with easy access to highways, and another six in the San Diego area. The flights were previously almost unknown in California.
The Border Patrol recently began encouraging agents in Imperial County to spend more time outside their vehicles because it is difficult to hear the aircraft over the hum of engines and air conditioners. The planes fly over farms and desert scrub near Calexico, a border town of about 40,000 residents. One pilot who recently eluded capture dropped a load of pot in a warehouse lot in city limits.
Until fences and vehicle barriers were erected, drug smugglers blended in with off-road vehicle enthusiasts in the Imperial Sand Dunes, used as a film location for "Star Wars: Return of the Jedi." Drug-laden Suburbans and Tahoes barreled through the desert scrub.
Drive-through smuggling attempts nearly stopped after fencing went up in 2008 and 2009. The number of drive-thrus in the Border Patrol's El Centro sector fell to six in fiscal 2010 from 340 in 2008.
That means smugglers are turning to tunnels and ultralights, Imperial County Sheriff Ray Loera told Congress this month.
"The problem now is that, as Clint Eastwood said, they adapt and overcome," he told lawmakers.
Still, the amount of pot being ferried on the ultralights pales compared to the multi-ton shipments through tunnels or the volume of seizures from secret vehicle compartments at border crossings every day, causing some authorities to wonder why drug traffickers would go to the trouble. In Imperial County, 10 seizures from ultralights drops since December have netted a relatively modest 3,090 pounds of marijuana.
"It makes you wonder how much they're really making off of this venture," said William Mataya, a group supervisor for ICE who belongs to an informal group of law enforcement officials in Imperial County that began meeting recently to swap intelligence on ultralights. "They're really not bringing a lot each time."
The risks can be fatal. A pilot died in November 2008 when his ultralight strapped with more than 140 pounds of marijuana crashed in a lettuce field in San Luis, Ariz. Another pilot who crashed in Arizona was paralyzed from the waist down.
Ultralights flying low are difficult to see on radars at March Air Force Base in Riverside, where CBP monitors air traffic along the entire border. That means relying on Border Patrol agents and sheriff deputies to be alert for the sound of unusual motors. They almost always get there too late to find the pilot of the planes, which cost $5,000 to $20,000.
"Either we get there and it's headed back, or it could already be back there," said Tim Jennings, who heads the Drug Enforcement Administration's Imperial County office.
Myers reported from Phoenix.