Definition
The paragraph of Title 14 of the Code of Federal Regulations (14 CFR) Part 91, Section 91.215(a), which establishes the technical performance and certification standards that an aircraft transponder and its automatic altitude reporting equipment must meet to be used in controlled airspace. It references the TSO (Technical Standard Order) requirements the equipment must satisfy.
Plain English
It's the specific FAA rule paragraph that says what kind of transponder you must have on board if you're going to use one in controlled airspace. It sets the equipment standard, not the rule about when you have to have one turned on.
Context Anchor
Seen in Class B operating requirements and preflight planning when checking whether an aircraft has the required equipment for busy controlled airspace around major airports.
Derivation
Section comes from a Latin word meaning “a cut” or “a part.” In regulations, a section is one numbered part of a larger set of rules; 91.215 is the section number, and (a) points to the first paragraph inside that section.
Why Pilots Care
Pilots must ensure their aircraft meets this requirement before entering Class B airspace to avoid violations and maintain safe ATC radar identification.
Intuition Check
Do not read section 91.215(a) as general advice or a checklist step. It is a precise legal citation: section 91.215, paragraph (a), in the federal aviation rules.
Example Sentence 1
The aircraft's transponder must meet the performance requirements of section 91.215(a) before it can be operated in Class B airspace.
Example Sentence 2
Section 91.215(a) transponder rules apply to most operations near major airports with Class B airspace.