SANDUSKY, Mich. - A Cessna touched down about midnight, dropped a load of drugs, and was back in the air in 90 seconds. Suddenly, the pilot of a U.S. border patrol helicopter hovering nearby turned on a powerful spotlight and tracked an SUV fleeing with hockey bags stuffed with 175 pounds of marijuana and 400,000 Ecstasy-type pills.

The bust by federal agents didn't happen on the southwestern border. It was in Michigan's rural Thumb region next to a soybean field. The remote airport in Sandusky offers a smooth runway at any hour to anyone who needs it, a perfect landing for drug smugglers who can cross the Great Lakes from Canada in minutes.

Beefed-up enforcement along the Mexican border has made smuggling more challenging for criminal cartels using the major southern routes, but drugs continue to flow across the porous northern border through such airstrips as officials look for new ways to fight back.

Tracking rogue planes at low altitude with their transponders off is "like trying to pick a needle out of a haystack," said John Beutlich of U.S. Customs and Border Protection, who oversees air and marine operations from Washington state to Maine.

Tiny airports feel helpless.

"Shoot, we're just a big cherry to pick and didn't realize it," said Joe Allen, manager of the Sandusky airport, 90 miles northeast of Detroit.

He installed a fence to keep cars from meeting planes at the runway, but the property is not staffed at night. Border agents could provide just two signs asking people to call an 800 number if they see something unusual.

Homeland Security Secretary Janet Napolitano says the United States hopes to start tapping into 22 Canadian radar installations to fill surveillance gaps on the border. Officials say the United States has one national radar network made up of feeds from the Federal Aviation Administration and the Defense Department.

Border authorities also conduct routine air patrols, but some lawmakers would like military-grade radar along with drones that could detect small aircraft.

"All everybody wants to talk about are drug cartels coming across the southern border. I don't mean to diminish that, but the northern border has gotten very little attention up until recently," said U.S. Rep. Candice Miller (R., Mich.), a senior member of the House Homeland Security Committee.

A new law requires the Obama administration to come up with an antidrug strategy on the U.S.-Canada border by summer.

Canada is a significant source of high-quality marijuana and the amphetamine Ecstasy. More than two million doses of Ecstasy were seized on the northern border in 2009, compared with just 312,000 doses in 2004, the Drug Enforcement Administration said, offering a snapshot of what's popular and what gets confiscated.

Most shipments come by road. But a 2009 flight from Ontario to Michigan, the subject of a recent federal trial, provided insight into drug operations that use small planes. Officials don't know how frequent such flights are, but they consider the vulnerability alarming.

Matthew Moody and nephew Jesse Rusenstrom, both from Amherstburg, Ontario, were the couriers captured that night in Sandusky. Their job was to enter the country through Detroit, meet the Canadian plane, and deliver the drugs to others in the United States. They also put 60 pounds of cocaine worth more than $500,000 on the return flight to Guelph, Ontario.

It was just one in a series of shipments. Rusenstrom said he met the plane at least 10 times at other tiny airports in the Thumb region - Marlette, Ray, Lapeer - as well as in Greenville in western Michigan and at an airport in Pennsylvania. The pilot activated runway lights from the cockpit, a standard practice.

Rusenstrom, 21, testifying at the trial of an accomplice, Robert "Romeo" D'Leone, said hundreds of airports were studied on Google Maps. "We would go around looking for airports, seeing if there was fences or cameras," he told the court.

D'Leone, who lives in the Toronto area, stopped his trial and pleaded guilty in April. Rusenstrom and Moody cooperated, pleaded guilty, and were recently sentenced to time served in custody. The United States still wants to extradite four others in Ontario who are accused of major roles, including the pilot.

Some jurors were alarmed by the revelations during the D'Leone trial. "You always hear Homeland Security has an eye on everything. It's surprising that airfields aren't manned 24 hours," Robert Simpson said.

"We're outside radar," Allen, the manager, said, running his finger over a map of Michigan's Thumb. "You can come and go as you please. You don't even have to file a flight plan."

Beutlich, the senior Customs and Border Protection official, said his agency's routine air patrols "can't be everywhere."

"I don't think there is more than just vigilance," he said, adding that law-abiding users of small airports typically were the best sources to report trouble.