As passengers file onto airplanes and their checked luggage is loaded below, most probably don't realize that as much as half the area beneath their seats will be filled with cargo, sent by commercial shippers.
Some in Congress say not nearly enough is done to screen that cargo.
"It is too risky to allow passengers to have cargo packages of this size under their feet on passenger planes which have not been screened," said Rep. Ed Markey, D-Mass., as he showcased a package at a press conference Thursday.
Commercial planes carry about 6 billion pounds of cargo each year. But of that, only about 15 percent is physically inspected. The government does the least direct checking of cargo from known commercial shippers. It's checked randomly. But packages whose shippers ask for specific flights are inspected.
Kip Hawley, director of the Transportation Security Administration, says it doesn't make sense to inspect every single cargo package. "It would be a waste of resources in that the threat might well be in the package, but it might be brought in by an insider," says Hawley. "There are many other ways that you can get a bomb into the system."
For that reason, the TSA has dramatically increased the number of dog teams that check cargo and even go inside the plane's cargo hold. And it checks the backgrounds of airport employees with access to planes and cargo.
But an aviation security expert says inspecting every package should be the goal.
"We want to be able to screen for radiation, for explosive materials, liquid and nitrogen-based explosives. All of those things need to be detected," says David Heyman, an aviation security expert.
At San Francisco International, the TSA will soon start a test program to see whether nearly 90 percent of cargo can be directly inspected — trying to answer how much screening is enough.