To enhance data transparency, section 519 of the FAA Reauthorization Act of 2018 requires the Federal Aviation Administration (FAA) to report to Congress on the costs allocable to and the total revenues received from users of air traffic services. In addition, the act requires our office to review and determine the validity of the model FAA uses to produce its report. Accordingly, we are initiating an audit of FAA’s Cost Allocation and Revenue Estimation Model (CAREM), which the Agency developed to produce its April 2021 report to Congress.