Trace amounts of radiation from Japan have been detected in Chicago and Dallas.
Travelers coming in from Japan Thursday triggered radiation detectors at O'Hare Airport in Chicago as they passed through customs.
In one instance, radiation was detected in a plane's air filtration system.
Radiation was also found in luggage and on passengers on flights from Japan.
Only very small amounts of radiation were detected, but airport officials are adding screenings and precautionary measures.
The U.S. is monitoring people and cargo coming back from Japan.
Also, Fort Worth-based American Airlines is flying non-stop routes from DFW Airport to Tokyo and back. What passengers don't see is a command center at American Airlines where company officials, union reps, and federal agencies monitor the radiation situation minute-by-minute.
Captain Sam Mayer, with the Allied Pilots Association, said, "They're planning flight plans that keep us away from any potential radioactive clouds that may be out there." He added, "They're doing modeling with the nuclear regulatory agency and the FAA."
In spite of the precautions, some pilots and flight attendants have chosen to beg off some of these trips.
Mayer explained, "Understand they're requested some vacation days in lieu of having to fly those trips."
Scrupulous screening has turned up some radiation. Medical equipment set off scanners on a DFW arrival Wednesday, according to Mayer. It didn't turn out to be anything major.
Also, incoming mail has been screened by the U.S. Postal Service.