Subject to the provisions of Section 1k, all tangible personal property to be used or consumed, within an enterprise zone established pursuant to the Illinois Enterprise Zone Act, by any aircraft maintenance facility, directly in the process of maintaining, rebuilding or repairing aircraft is exempt from the tax imposed by this Act. The exemption includes repair and replacement parts for machinery and equipment used primarily in the process of maintaining, rebuilding or repairing aircraft, and also includes equipment, fuels, material and supplies for the maintenance, repair or operation of such machinery or equipment.