It's an oft-repeated phrase with enormous implications: "The terrorists only have to be right once; we have to be right all of the time." This time it comes from Congressman Jason Chaffetz, R-Utah, who is voicing skepticism about how federal agencies are working to keep American fliers safe.

"I worry that we've got security theater, that we're not actually making the airports more secure," Chaffetz says.

From body scanners to exceptionally thorough pat-downs, Chaffetz believes there are more effective technologies available that are also less intrusive.

There's no arguing that for ten years there's been no terror attack on U.S. soil that begins to approach the scale of what we experienced on 9/11. TSA Administrator John Pistole says the layers of airport security are necessary and effective.

"I think the vast majority of people recognize that ... all those things that we do are for their own safety and protection," Pistole said.

Aviation Safety Expert Brian Jenkins, of the RAND Corporation, says law enforcement agencies must be careful not to push fliers too far. "You cannot risk turning those passengers you are trying to protect into adversaries of the very systems you use to protect them," Jenkins cautions.

Chaffetz says authorities must find a way to beef up security and make procedures less invasive. "We shouldn't have to give up every civil liberty in order to secure an airplane," he said.

Pistole is well aware of the delicate equation. "There's obviously a balance between safety, security and privacy," he noted.

A new Fox News poll reveals that 54 percent of Americans feel safer now that they did before September 11, 2001. Thirty-three percent report that they feel less safe, with 11 percent saying our safety is unchanged.

Homeland Security Secretary Janet Napolitano admits that threats are constantly evolving and that terrorists aren't just working toward large-scale attacks.

"What we see instead now are smaller plots involving fewer people," Napolitano said, adding that those smaller plots "are much more difficult to intercept."

Those threats clearly aren't grounding U.S. fliers. Last year, some 720 million passengers took flight. That's an eight percent increase over the year prior to the 9/11 attacks.