Though it takes a sick mind, it isn't hard to bomb a U.S. airliner. The security equipment in place at the nation's airports was mandated in the 1970s, when the chief concern was hijackings, not terrorist bombings. So while the metal detectors we all step through can uncover guns, knives, and other metal weapons, they can't find hidden explosives. Neither can the x-ray machines that scan carry-on bags, as well as checked luggage for international flights. Checked luggage and mail for domestic flights are not examined at all.

But recent bombings in Oklahoma City and Atlanta's Olympic Park, the FBI's discovery of plots to blow up U.S. airliners, and speculation about the downing of TWA Flight 800 in July have produced strong calls for protection against demolition-minded terrorists. Politicians have been jolted into action. After years of little legislative attention, Congress on October 9 suddenly appropriated $160 million for the Federal Aviation Administration (FAA) to rush more than 500 bomb detection units of various types into airports for a year of testing.

Some observers say this action is long overdue. Others say it is too hasty. No fewer than 10 detection schemes are vying for position-from x-ray machines and magnetic resonance imagers to chemical-vapor sniffers. Although they have different pros and cons, no single machine is both fast enough and accurate enough to meet the FAA's certification criteria. All the proposed systems are expensive. They also raise serious social concerns. The National Research Council (NRC) recently concluded that ultimately "limitations on the technology will be imposed as a result of passenger intolerance for invasion of privacy, delays, or discomfort."

Even if the technical and human issues are resolved, the biggest question remains: Who will pay to protect the skies, and is the price worth paying?