1. Receipts from:
a. sales of aircraft and repairs thereto including machinery or equipment to be installed on such aircraft and replacement parts therefor when utilized by an air carrier as defined by the Civil Aeronautics Board or the Code of Federal Regulations having its principal place of operations within the State and engaging in interstate, foreign, or intrastate air commerce; and
b. repairs on aircraft having a maximum certificated takeoff weight, as contained in the certificate type issued by the Federal Aviation Administration, of 6,000 pounds or more, including machinery or equipment to be installed on such aircraft and replacement parts therefor;
are exempt from the tax imposed under the Sales and Use Tax Act.