Two ranking members of the House Homeland Security Committee have requested an audit of how the Transportation Security Administration (TSA) deploys controversial full-body scanners at airport security checkpoints.

SinceUmar Farouk Abdulmutallab's plot to ignite explosives stashed in his underwear failed to bring down a Detroit-bound international flight on Christmas Day 2009, the TSA has deployed about 640 full-body scanners to 165 airports to detect nonmetallic threats to aviation security.

In a letter (.pdf) to the Government Accountability Office (GAO), ranking member Bennie G. Thompson (D-MS) and Rep. Sheila Jackson Lee (D-TX), ranking member of the Subcommittee on Transportation Security, asked for the audit after learning of full body scanner "utilization concerns" the GAO disclosed in a recent report.

These concerns were highlighted yesterday by the GAO beforea joint-committee hearing on TSA effectiveness. Between March 2010 and February 2011,  the GAO discovered already deployed full body scanners were underused or inappropriately deployed, testified Stephen Lord, director for homeland security and justice issues at the GAO.

"During this time period, some of the deployed AIT units were used on less than 5 percent of the days they were available since their deployment. Additionally, some units were used on less than 30 percent of the days available since their installation,"according to Lord's prepared testimony (.pdf). "Moreover, we reported that at some of the 12 airports we visited, AIT units were deployed but were not regularly used. For example, at one airport we observed that TSA had deployed 3 AIT units in an airport terminal that typically handles one flight a day of approximately 230 passengers."

The audit, say Thompson and Lee, would determine if TSA has deployed the machines, the majority of which were purchased with stimulus funds, successfully and efficiently. Each machine costs approximately $170,000, which doesn't take into account installation, upgrade, or staffing costs.