14 C.F.R. § 25.1301 Function and installation.
Title 14 - Aeronautics and Space
Each item of installed equipment must— (a) Be of a kind and design appropriate to its intended function; (b) Be labeled as to its identification, function, or operating limitations, or any applicable combination of these factors; (c) Be installed according to limitations specified for that equipment; and (d) Function properly when installed.
Title 14: Aeronautics and Space
PART 25—AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
Subpart F—Equipment
General
§ 25.1301 Function and installation.