Definition
A federal regulation that prohibits operating an airplane under instrument flight rules (IFR) in controlled airspace unless the altimeter, the static pressure system, and each automatic pressure altitude reporting system have been tested and inspected within the preceding 24 calendar months and found to comply with the standards in Appendix E of Part 43.
Plain English
A rule that says you can't fly IFR in controlled airspace unless your altimeter and related pressure systems have been tested by an authorised person within the last 24 calendar months.
Context Anchor
Seen during preflight review of aircraft maintenance records, especially when confirming whether the aircraft is legal for IFR flight.
Derivation
14 CFR' means Title 14 of the Code of Federal Regulations, which is the section of US federal law covering aeronautics and space. 'Part 91' is the chapter covering general operating and flight rules. 'Section 91.411' is the specific numbered rule within that part. The numbering helps pilots and mechanics cite a single rule precisely.
Why Pilots Care
Ensures the altimeter is accurate for safe altitude management and satisfies legal requirements for IFR flight and certain controlled airspace.
Intuition Check
Do not read this as just a paperwork reference. It points to a required equipment inspection that affects whether the aircraft can legally be used for certain IFR operations.
Example Sentence 1
Before accepting the aircraft for an IFR cross-country, the pilot checked the logbook to confirm the 14 CFR part 91, section 91.411 inspection was within the last 24 calendar months.
Example Sentence 2
Before an IFR flight the crew verified that the altitude reporting equipment met the inspection interval required by 14 CFR part 91, section 91.411.