FBI imposes new restrictions on crop-dusters

WASHINGTON (CNN) -- The FBI has limited the use of crop-dusters amid concerns that suspected terrorists might have been plotting to use the aircraft for another attack, possibly chemical or biological, according to law enforcement sources.

The FBI grew alarmed about crop-dusters after a crop-dusting manual was discovered among the belongings of a man being held as a material witness in the investigation into the September 11 terrorist attacks against the World Trade Center and the Pentagon.

Zacarias Moussaoui was arrested last month in Minnesota on an alleged passport violation. Moussaoui was in custody at the time of the attacks.

Moussaoui apparently had raised suspicions because he sought training in flying commercial jets at flights schools in Oklahoma and Minnesota but showed no interest in learning about takeoffs or landings.

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Last week, the FBI imposed a ban on crop-dusting but has since modified it to keep crop-dusters away from metropolitan areas.

The National Agricultural Aviation Association posted the following statement on its Web page, saying it had come from the FBI:

"Members should be vigilant to any suspicious activity relative to the use, training in or acquisition of dangerous chemicals or airborne application of same, including threats, unusual purchases, suspicious behavior by employees or customers and unusual contacts with the public. Members should report any suspicious circumstances or information to local FBI offices."

The statement added that agricultural aviators were allowed to fly except near major metro areas.

In Belle Glade, Florida, crop-duster mechanic James Lester said he believes that Mohamed Atta, one of the suspected hijackers who slammed a plane into the World Trade Center's north tower, had come out to the airstrip twice, along with other men he described as "Arab-looking."

"They wanted to know (the) capacity of the airplane, how much would the airplane hold, how much fuel and how to crank it," he said.

Defense Secretary Donald Rumsfeld would not rule out the possibility that terrorists were planning another attack, using chemical or biological weapons.

"We can't know that for certain. We can suspect it," Rumsfeld said on CBS' "Face the Nation" program.

He noted that several countries the United States views as terror sponsors "have very active chemical and biological warfare programs. And we know that they are in close contact with terrorist networks around the world."

For its part, the FBI refused to comment specifically on its focus on crop-dusters.

"In an abundance of caution, the FBI has taken a number of steps in reaction to every bit of information and threats received during the course of this investigation," an FBI statement said.