WASHINGTON, July 31 (Reuters) - The Federal Aviation Administration has failed to resolve persistent issues with SkyWest Airlines' SKYW.O maintenance practices, a government report said Thursday.

The Transportation Department Office of Inspector General said SkyWest, the largest U.S. regional airline that operates flights for United Airlines UAL.O , Delta Air Lines DAL.N, American Airlines AAL.O, and Alaska Airlines ALK.N, said FAA safety inspectors have been unable to fully resolve issues pertaining to remote return to service maintenance practices for more than four years.