Not to worry

MINNEAPOLIS (AP) -- Minneapolis-St. Paul International Airport, along with 428 other airports around the United States, will begin mandatory inspections of all checked baggage for explosives, officials said.

But Northwest Airlines, the main carrier at the airport, said the new rules should not inconvenience passengers. "This shouldn't add any significant time to travelers' checking in," said Dirk McMahon, the airline's senior vice president of customer service.

The enormous undertaking -- an estimated 1.5 billion bags are checked in at U.S. airports every year -- is one of the security measures ordered by Congress after the September 2001 terrorist hijackings.

The checked baggage screenings were to begin Wednesday.

Previously, only a small portion of checked bags were screened. Now, 90 to 95 percent of checked bags will be run through screeners that detect explosives, or through other machines that sense explosive residue.

"If a bag hasn't been screened, it won't go on the plane," said Brian Turmail, spokesman for the Transportation Security Administration, the federal agency responsible for airport security.

The agency advises travelers not to lock their checked bags. Otherwise, security workers who need to look inside them may have to break the locks. Northwest continues to recommend that domestic passengers arrive 75 minutes before departure and international travelers, two hours.

Travelers are also counseled to forego packing cheese and other foods in checked bags. Bomb screening machines may mistakenly flag them as explosives. The problem is the machines use the same technology as a hospital CT scan to sense the density of explosives. And some foods and explosives are similar in density.

Also, books should be spread throughout bags. If they're stacked, they can block images of objects behind them.

More than 400 airports have enough screening devices to inspect 90 to 95 percent of bags, according to the TSA. Five to nine airports that lag in the deployment of the screeners will use explosive-sniffing dogs and other alternative checks to augment electronic screenings.