FAR Ninety-One Point Four Eleven, the Altimeter Inspection Every IFR Pilot Needs, and the Transponder Rule That Also Applies on VFR Days in Controlled Airspace
FAR 91.411 and 91.413 require 24-calendar-month inspections of your altimeter/static system and transponder - rules that catch pilots off guard more than almost any others in Part 91.
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