14 CFR § 121.342
Pitot heat indication systems
July 13, 2020
No person may operate a transport category airplane or, after December 20, 1999, a nontransport category airplane type certificated after December 31, 1964, that is equipped with a flight instrument pitot heating system unless the airplane is also equipped with an operable pitot heat indication system that complies §25.1326 of this chapter in effect on April 12, 1978.
[Doc. No. 28154, 60 FR 65932, Dec. 20, 1995]