14 CFR § 91.213
Operations without a MEL
and
Inoperative instruments and equipment
14 CFR § 91.205
Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements
49 CFR Part 830
NOTIFICATION AND REPORTING OF AIRCRAFT ACCIDENTS OR INCIDENTS AND OVERDUE AIRCRAFT, AND PRESERVATION OF AIRCRAFT WRECKAGE, MAIL, CARGO, AND RECORDS
43 Appendix A
Preventive Maintainance
91.203
Airworthiness requirements