Definition
A federal aviation regulation that prohibits any person from operating an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 mph), unless otherwise authorized by the Administrator.
Plain English
Below 10,000 feet above sea level, you are not allowed to fly faster than 250 knots indicated airspeed. This is a hard speed limit set by the FAA, not a guideline.
Context Anchor
Seen in airspeed limitation discussions, descent planning, instrument procedure training, and reviews of the federal operating rules for flight under Part 91.
Derivation
14 CFR means Title 14 of the Code of Federal Regulations, which is the section of U.S. law dealing with aviation. Part 91 covers general operating and flight rules. The number 91.117 identifies the specific rule, and (a) is the first paragraph within it. Reading it as 'Title 14, Part 91, section 117, paragraph a' makes the citation easier to navigate.
Why Pilots Care
This speed limit reduces collision risk in higher-traffic altitudes and supports orderly traffic flow near airports and in terminal areas.
Analogy
A regulation citation works like an address. “14 CFR” is the neighborhood, “Part 91” is the street, “91.117” is the building, and “(a)” is the exact room where this speed rule is found.
Grounding Statement
Below 10,000 feet above sea level, think of 250 knots indicated as the normal upper speed limit unless official authorization changes it.
Intuition Check
“Part” here does not mean a physical airplane part. It means a major division of the federal aviation rules, and 91.117(a) is one specific paragraph inside that division.
Example Sentence 1
Passing through 10,000 feet MSL on the descent, the crew reduced thrust to slow below 250 knots to comply with 91.117(a).
Example Sentence 2
During the approach briefing the crew confirmed they would observe the 250-knot restriction imposed by 14 CFR Part 91 — 91.117(a).