JACKSONVILLE, Fla. -

There's a battle brewing over how safe the public is on airplanes. The Federal General Accounting Office (GAO) is questioning the validity of a program the Transportation Agency has spent nearly a billion dollars on.

The program uses so-called behavior detection officers at airports around the country. That behavior detection is an attempt to weed out terrorists from being among air passengers.

Channel 4 spoke with people at Jacksonville airport Wednesday night, who thought the program sounded like a good idea.

"They're just trying to provide safety for the general public," said traveler, Mike Netting. "So if they see somebody acting peculiar in line, they should take them aside and see what's going on."

Here's how it works: About 3,000 screeners at U.S. airports watch passengers for signs of stress, fear or deception, something they are trained to do.

Channel 4 crime and safety analyst Ken Jefferson said the practice is actually pretty common within law enforcement agencies. Jefferson said it's not an exact science, but it's still valuable.

"There are valid clues that can come from watching people in line," said Jefferson. "Do they appear fidgety? Are they sizing up what security measures are? There are several things people can look at and look for," said Jefferson.

The head of the TSA is expected to answer questions about the program at a hearing with the Homeland Security Committee on Thursday.