International air carriers break U.S. federal law every day. Any cargo flown on a passenger plane in U.S. airspace (whether of domestic or foreign origin) must be screened for explosives. Yet, despite the law, some cargo flown into the United States does not meet the “100 percent” standard.

It has been over a year since a congressional deadline to screen all cargo on passenger planes. While the Transportation Security Administration (TSA) initially said meeting the 100 percent mandate for international cargo would take several years, it announced last spring that everything would be screened in full by Dec. 31, 2011. This is not because foreign governments are bowing and adhering to U.S. security protocol; rather, TSA is adjusting how it interprets the mandate.

In 2007, Congress passed the Implementing Recommendations of the 9/11 Commission Act of 2007 (9/11 Act). The law addressed myriad homeland security issues, among them, cargo screening. Industry was given three years to comply with a mandate to screen for explosives all cargo transported on passenger planes. When the deadline arrived, domestic cargo met the law, and international cargo did not.

In March, TSA Assistant Administrator John Sammon explained the challenge for the House Homeland Security Subcommittee on Transportation: “Closing the final [screening] gap poses some operational challenges for airlines. More importantly, TSA does not have the same inspection and compliance authorities overseas that it has in the United States.”

This was always the challenge – beyond the logistical and resource challenges airlines face with 100 percent screening, no U.S. agency has the authority to compel a foreign government to meet an American security mandate. Congress asked the impossible.

Yet, when terrorists in Yemen shipped bombs disguised as printer cartridges in October 2010, it reinvigorated the debate over cargo screening, and for some, underscored the need for urgent action. No matter that the potentially lethal shipments were sent via UPS on all-cargo planes (and not in the belly of a passenger-laden 777), soon after the incident TSA announced an end-of-the-year deadline.

Had anything changed to make the mandate possible? Did foreign security agencies alter how they approached operations and agree with the congressional 100 percent preference? Changes came not from abroad but from within TSA. Consider the law:

‘‘[The 100 percent cargo screening system] shall require, at a minimum, that equipment, technology, procedures, personnel, or other methods approved by the Administrator of the Transportation Security Administration, are used to screen cargo carried on passenger aircraft…to provide a level of security commensurate with the level of security for the screening of passenger checked baggage.”

The heart of the law is not necessarily a physical screening of every shipment (though that is the standard for domestic cargo screening) but rather achieving a level of security commensurate with baggage screening, which is scanned piece by piece. Semantically speaking, TSA need only deem a foreign security process as achieving a level of security equal to 100 percent screening for said process to satisfy the international inbound cargo screening mandate.

“This approach is TSA’s only viable option under the law,” said Jeffrey Sural, former legislative counsel at TSA. “It does not make for a sound screening system. The mandate is an arbitrary metric, and it is the nature of a bureaucracy, from leadership on down, to make meeting that mandate or the commensurate threshold a priority. Finding the threat becomes secondary.”

Sural, who was TSA’s lead negotiator and counsel for all legislation introduced to Congress, including the 9/11 Act, said the screening mandate is flawed because it “does not allow TSA the flexibility or adaptability to be risk-based…Congress can and should exercise oversight of management, operations and metrics, but establishing concrete mandates in law may not be the best way to create a robust screening program, whether it is international cargo, domestic checked bags, or people.”

TSA’s decision on inbound cargo screening comes at a time when TSA Administrator John Pistole, Homeland Security Secretary Janet Napolitano and other DHS leaders are advocating the department’s risk-based approaches to security challenges. For air cargo security, it means forcing a square peg (100 percent cargo screening) into a round hole (risk-based screening).

DHS has long championed risk-based security (since before Pistole et al’s recent remarks), but experts warn for that security philosophy to be effective, it must be executed in word and deed.

“There are potential deadly results of TSA compromising on acceptable standards,” said Erroll Southers, President Obama’s first nominee to head the TSA. “Ultimately, TSA’s ‘risk-based and intelligence-driven’ sound bites need to finally have some teeth if the system is to work and be deemed credible.”

Southers, Associate Director at the National Center for Risk & Economic Analysis of Terrorism Events (CREATE), said the “teeth” of such a screening system refers to deep intelligence and knowledge of “point-of-origin” countries and supply chains that present a high threat profile. Meeting congressional law is important, but it will only evolve and work if American security agencies have the necessary relationships with countries that present the greatest security challenges.