This rulemaking would amend 14 CFR part 241 to require monthly reporting on the number of passengers transported and/or enplaned on flights that are marketed by mainline U.S. air carriers, but operated by the mainline carrier's regional codeshare affiliates under the mainline carrier's brand. Mainline carriers, in addition to operating their own flights, contract with other airlines, who operate flights under the mainline carrier's brand. With this new data, the Department would be able to rank U.S. air carriers on the complaints that they received based on the flights they market (as opposed to only flights they operate) in its monthly Air Travel Consumer Report (ATCR) and the flying public would see a more complete picture of the performance of these airlines, which will make the ATCR even more useful to consumers.