NEW YORK, United States Federal investigators are piecing together details of an audacious new trend in drug smuggling: South American gangs are buying old jets, stuffing them full of cocaine and flying them across the Atlantic to feed Europes growing coke habit.

At least three gangs have struck deals to fly drugs to West Africa and from there to Europe, according to United States indictments. One trafficker claimed he already had six aircraft flying. Another said he was managing five airplanes. Because there is no radar coverage over the ocean, big planes can cross the Atlantic virtually undetected.

The skys the limit, one Sierra Leone trafficker boasted to a Drug Enforcement Administration informant, according to court documents.

The new air route is remarkable because of the distances involved and the complexity of flying big jets, said Scott Decker, a criminology professor at Arizona State University who studies smuggling methods. A trip from Venezuela to West Africa is about 3,400 miles (5,500 kilometres) about triple the distance to Florida.

The United Nations Office on Drugs and Crime began warning about trans-Atlantic drug planes after November 2, 2009, when a burned-out Boeing 727 was found in the desert in Mali. Drug smugglers had flown the jet from Venezuela, unloaded it and then torched the aircraft, investigators said.

In some cases, executive jets have been used, including a Gulfstream II that landed in Guinea-Bissau in 2008 and another Gulfstream seized in 2007 as it tried to depart Venezuela for Sierra Leone.

In the last year, a flurry of arrests has begun shedding light on how the air routes work. The cases are being prosecuted in a New York federal court because some of the cocaine was supposed to have been sent to the United States.

The quantity of cocaine distributed and the means employed to distribute it were extraordinary, prosecutors wrote in one case. They warned of a conspiracy to spread vast quantities of cocaine throughout the world by way of cargo airplanes.

In some ways it is a throwback to the 1970s and 80s, when drug pilots flew freely between Colombia and staging areas near the US border, Decker said. Back then, drug lords such as Amado Carrillo, nicknamed The Lord of the Skies, sent jets with as much as 15 tons of cocaine from Colombia to northern Mexico.