‘Dirty Bomb’ a Fear in Scrubbed Flights

The terror alert that caused the cancellation of several transatlantic flights this weekend was based partly on intelligence that Al Qaeda might use chemical, biological or radiological weapons in an aviation attack, a U.S. official familiar with the case said Sunday.

“A chemical, biological or ‘dirty bomb’ attack has always been a concern with regard to aviation,” said the official, speaking on condition of anonymity. “And that was one of the concerns in this case.”

After the U.S. government warned Saturday of “a specific and credible threat,” British Airways canceled two London-Washington round trips and a London-Miami flight, while Air France grounded two Paris-Washington flights. Those flights were scheduled for Sunday and today.

On Sunday, Continental Airlines canceled a flight from Washington to Houston due to arrive while the Super Bowl was being played at Reliant Stadium, about 28 miles from the international airport. That action came a day after Continental grounded a flight from Glasgow, Scotland, to Los Angeles.

“There was specific threat information on Continental Flight 1519 from Washington to Houston, and that information was shared with the airline,” said Suzanne Luber, a spokeswoman for the Department of Homeland Security in Washington. “We don’t have any information that it was connected to the Super Bowl. It was a specific threat related to the flight number and the date, but not as to what kind of threat.”

Since December, law enforcement and intelligence agencies in the U.S. and Europe have detected signs that terrorists might have been plotting an airborne attack. The primary concerns were that terrorists would smuggle a bomb aboard a plane or attempt a Sept. 11-style hijacking to use a plane as a missile against an American target.

U.S. authorities put out an alert about smuggled explosives after the November arrest of a British suspect who allegedly rigged plastic explosives in a pair of socks connected by a piece of string -- a device he allegedly intended to use to sneak a bomb-making kit past airport security.

But a flurry of intelligence in December that led to eight cancellations of U.S.-bound flights, including six Paris-Los Angeles trips before Christmas, also made reference to unconventional weapons, according to the senior U.S. official.

“The alert about flights did not exclude a possible chem, bio or radioactive attack last time, in December,” the official said. “But this dimension of the threat seems to be more developed in the intelligence this time.”

The possibility of smuggling a biological agent onto an airplane poses a distressing new danger, a key U.S. senator said Sunday.

“Nobody has any idea about what to do about [biological agents] on an airplane or on the ground,” Sen. John D. “Jay” Rockefeller IV (D-W.Va.), vice chairman of the Senate Select Committee on Intelligence, said on “Fox News Sunday.”

“That’s partly the problem of not checking cargo, and it’s partly the problem of biological weapons, which nobody has figured out really what do about yet.... It’s very dangerous.”

Police in France and Britain have broken up two related plots that allegedly involved attacks with crude poisons, including cyanide and ricin. In late 2002, French police found a special protective suit designed for handling nuclear and toxic materials when they arrested a number of Algerians accused of plotting a cyanide gas attack on the Russian Embassy in Paris.

In a related operation weeks later, British police rounded up more Algerian suspects and found a crude lab for producing ricin, a poison with no antidote, in a London apartment.

Despite the previous cases involving unconventional weapons in Europe, the threat that led to this weekend’s cancellations may involve terrorists based elsewhere who decided to target Air France and British Airways planes, the U.S. official said.

Times staff writer David G. Savage in Washington contributed to this report.