A report by the union representing U.S. Airways suggests that terrorists may have conducted dry runs on commercial flights throughout the country, the Montgomery Advertiser reported.

According to the US Airlines Pilots Association memo, "there have been several cases recently throughout the (airline) industry of what appear to be probes, or dry runs, to test our procedures and reaction to an in-flight threat." 

The most recent run occurred on a flight from Washington, D.C.'s Reagan National Airport that was headed toward Orlando, Fla. In the memo, it states that four "Middle Eastern" men created a disturbance in several instances.

One witness claimed one of the men ran from his coach seat to the flight deck door, then made a quick left and entered the bathroom where he remained "for a considerable length of time." 

As the first man stayed in the bathroom, the other three began switching seats and opening overhead compartments, "generally making a scene." It seemed as if they were trying to distract flight attendants, the memo said.

U.S. Airways declined to comment on the incident but said they are working closely with authorities. 

Dr. Jeff Addicott, a terrorism expert, said the dry runs are not surprising.

"That's one of the things that law enforcement looks for," Addicott said. 'Terrorism is not a random act.  It's directed, it's thought out and therefore that requires a practice, or a training mission."

He added that flight passengers can be vital in discovering potential terrorists on flights and prevent attacks as a result.

"The funding has kind of dried up and so the vast majority of flights do not have air marshals on them," he says. "The first line of defense is really passengers."

Wolf Koch, a pilot for Delta Airlines, said several crews are concerned the dry runs are being carried out in preparation for another 9/11-type attack.

Koch, who also works as Aviation Security Committee Chairman for another union, the Air Line Pilots Association International, called 9/11 an "incredible attack on us" and said it was "very well orchestrated and they're going to try it again... 100%, no question in my mind. They're going to try it again."