The Missouri Department of Revenue has issued a letter ruling discussing the taxability of aircraft parts and accessories sold as part of installations and repairs (Mo. Ltr. Rul. No. LR 7002 (Dept. of Revenue Dec. 20, 2011)). The sale of materials, replacement parts, and equipment used directly in the "modification, replacement, repair, and maintenance of aircraft, aircraft power plants, and aircraft accessories," are specifically exempt from tax. This is true regardless of whether the charges for these services are separately stated on the customer's bill.