The Department of Transportation's Office of Inspector General is planning to conduct an audit of the National Airspace System (NAS) that could become a key point of information for the looming battle over how to fund the FAA. In an internal memo obtained by AVweb, David Tornquist, the DOT's Assistant Inspector General for Competition and Economic Analysis, sets as his goal nothing less than putting a dollar figure on each type of airspace usage in the context of the various funding alternatives currently being bandied about for the FAA. "Evaluating these alternatives requires a common understanding of who currently uses the NAS and how that usage affects the FAA's costs and how closely the alternatives mirror use of FAA services," the memo reads. The process began July 31 with a request from then-Aviation Subcommittee Chairman John Mica, R-Fla., to have the OIG nail down the basis for the myriad issues that will be raised by the FAA's seeming intention to abandon the current method of funding -- fuel, ticket and cargo waybill taxes -- in favor of a pay-as-you-go system based on cost impact to the NAS. General aviation groups are opposing the user-fee initiative while airlines are supporting it.