U.S. extends ban on crop-dusters

WASHINGTON (CNN) -- Citing "national security," the U.S. Federal Aviation Administration has extended a ban on crop-dusters through Tuesday, September 25 at 12:05 a.m. in each time zone, a move prompted by FBI concerns of a possible biological or chemical terrorist attack.

In addition, no aircraft capable or equipped for agricultural operations is allowed to operate -- except firefighting tankers with emergency authorization, according to FAA spokesman Frasier Jones.

The ban, which applies to the 48 contiguous states, comes amid concerns by the FBI that terrorists might have been plotting to use the seemingly innocuous aircraft for another attack, according to law enforcement sources.

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The FBI said Monday it had no specific evidence of a planned chemical or biological attack, but recommended to the FAA that it ground crop-dusters as a precaution.

A ban was first imposed last week and then modified to keep crop-dusters away from metropolitan areas.

The FAA also has ordered that all aviation employees with badge access to restricted areas have their employment histories scrutinized, and may possibly call for criminal background checks on them.

In Florida, the state Department of Agriculture will establish a stricter security protocol regarding the use of crop-dusters, according to spokesman Terry McElroy.

He said the department was working with the Florida Department of Law Enforcement and the FBI on the matter. He said the states already requires the registration and licensing of crop-dusters, but there will be more coordination with law enforcement.

"There will be a system of tight reins," McElroy said. "They will have to notify us if and when they go up, and share tail numbers with law enforcement."

Interest in crop-dusters in Florida

The interest in crop-dusters in Florida is particularly acute because law enforcement sources said one man now accused by U.S. investigators of being a hijacker on board a jet that slammed into the World Trade Center September 11 had wanted to buy a crop-dusting plane there.

Crop-duster mechanic James Lester said he believes that Mohamed Atta, one of the alleged hijackers who crashed a jet into the World Trade Center, had twice come out to the air strip in Belle Glade, Florida, along with other men he described as appearing to be from the Middle East.

"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. Law enforcement sources said they believed Atta and some Middle Eastern colleagues had indeed visited the air strip.

Law enforcement sources said Atta had also inquired about a loan for a plane purchase at a Homestead, Florida, bank.

The FBI grew alarmed about crop-dusters after a crop-dusting manual was discovered among the belongings of a man now being held as a material witness in the investigation into the 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 last week's attacks.

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

-- CNN correspondents Kelli Arena, Patty Davis and Susan Candiotti contributed to this report.