Nothing in this chapter shall apply to or be construed or held to apply to:
(1) The transportation or handling of United States mail; or
(2) Any common carrier by aircraft which the Arkansas Department of Transportation shall by order determine to be engaged mainly and principally in interstate commerce and whose intrastate business is incidental to its interstate business, if the department finds that its operations are conducted pursuant to a certificate of public convenience and necessity issued by the Federal Aviation Administration or any other governmental agency successor thereto.