14 CFR § 91.187 - Operation under IFR in controlled airspace: Malfunction reports.
(a) The pilot in command of each aircraft operated in controlled airspace under IFR shall report as soon as practical to ATC any malfunctions of navigational, approach, or communication equipment occurring in flight.
(1) Aircraft identification;
(2) Equipment affected;
(4) Nature and extent of assistance desired from ATC.