14 CFR § 25.1301 - Function and installation.
(a) Each item of installed equipment must -
(1) Be of a kind and design appropriate to its intended function;
(2) Be labeled as to its identification, function, or operating limitations, or any applicable combination of these factors;
(3) Be installed according to limitations specified for that equipment; and
(4) Function properly when installed.
(b) EWIS must meet the requirements of subpart H of this part.