Definition
The Federal Aviation Regulation that requires the static pressure system, altimeter instrument, and automatic pressure altitude reporting equipment of an aircraft to be tested and inspected within the preceding 24 calendar months before that aircraft may be operated under instrument flight rules (IFR) in controlled airspace.
Plain English
A rule that says the parts of your aircraft that measure altitude and report it to air traffic control must be checked and approved within the last 24 months before you can fly in the clouds or otherwise rely on instruments in controlled airspace.
Context Anchor
You will see this citation in aircraft maintenance records, inspection status lists, IFR readiness checks, and discussions of whether an aircraft is legal to fly in controlled airspace under instrument flight rules.
Derivation
The numbering follows the structure of the Code of Federal Regulations. '14 CFR' means Title 14 (Aeronautics and Space) of the Code of Federal Regulations, 'part 91' covers general operating and flight rules, and 'section 91.411' is the specific paragraph within that part. Knowing the structure helps you find any FAA rule quickly once you understand the title-part-section format.
Why Pilots Care
Accurate altimeter readings are essential for vertical separation from terrain and other traffic; an overdue inspection can ground the aircraft or invalidate IFR operations.
Intuition Check
“Part” and “section” do not mean airplane parts or textbook sections here. They are location markers in the federal aviation rulebook: Part 91, Section 91.411.
Example Sentence 1
Before filing the IFR flight plan, the pilot checked the maintenance logs and confirmed the section 91.411 inspection was current.
Example Sentence 2
During the annual inspection the avionics shop performed the required static-system leak and altimeter accuracy tests to satisfy 14 CFR part 91 section 91.411.