Definition
The section of Title 14 of the Code of Federal Regulations that sets maximum indicated airspeed limits for aircraft operating in U.S. airspace below 10,000 feet MSL, within Class B, C, and D airspace, and beneath Class B shelves. The principal limits are 250 knots below 10,000 feet MSL, 200 knots in Class C and D airspace at and below 2,500 feet AGL within 4 nautical miles of the primary airport, and 200 knots beneath Class B airspace or within a VFR corridor through Class B.
Plain English
The federal rule that tells pilots how fast they're allowed to fly in busy or low-altitude airspace. Below 10,000 feet you generally can't exceed 250 knots, and the limit drops to 200 knots near smaller towered airports and under the shelves of large Class B airspace.
Context Anchor
Seen in AIM and regulation discussions about aircraft speed limits, especially near airports, below 10,000 feet, and around Class B airspace.
Derivation
CFR' stands for Code of Federal Regulations. Title 14 covers Aeronautics and Space. 'Section 91.117' is the specific numbered rule within Part 91 (General Operating and Flight Rules) that addresses aircraft speed.
Why Pilots Care
Following these limits prevents airspace violations, maintains safe separation from other aircraft, and avoids FAA enforcement action.
Intuition Check
Do not treat 14 CFR section 91.117 as a handbook suggestion. It is a federal operating rule about aircraft speed limits.
Example Sentence 1
Descending through 10,000 feet, the captain reduced power to comply with 14 CFR section 91.117 and keep the aircraft at or below 250 knots indicated.
Example Sentence 2
Before entering the Class C airspace, the student double-checked 14 CFR section 91.117 to confirm the 200-knot speed limit applied inside four nautical miles of the airport.