FAR 91.411: Altimeter system and altitude reporting equipment tests and inspections. (a) No person may operate an airplane, or helicopter, in controlled airspace under IFR unless— (1) Within the….
FAR 91.413: ATC transponder tests and inspections. .(a) No persons may use an ATC transponder that is specified in 91.215(a), 121.345(c), or §135.143(c) of this chapter unless, within the….