Definition
A federal aviation regulation that limits aircraft indicated airspeed to 200 knots when flying in the airspace underlying Class B airspace, or in a VFR corridor designated through Class B airspace.
Plain English
When you are flying just below a Class B shelf, or through a VFR corridor cut into Class B, your speed is capped at 200 knots indicated.
Context Anchor
Seen when studying airspeed limits, operating near Class B airports, or planning a visual route through or under busy controlled airspace.
Derivation
CFR stands for Code of Federal Regulations. Part 91 is the section covering general operating and flight rules. The numbering 91.117 identifies the specific rule on airspeed, and (c) is the third paragraph within that rule.
Why Pilots Care
The limit reduces closure rates and traffic conflicts in high-density areas immediately below busy terminal airspace.
Intuition Check
Do not treat this as just a handbook reference; it points to a rule pilots are required to follow. Also, the 200-knot limit is based on indicated airspeed, the speed shown in the cockpit, not how fast the airplane is moving across the ground.
Example Sentence 1
Flying beneath the LAX Class B shelf at 2,500 feet, the pilot kept the aircraft at 190 knots indicated to comply with 91.117(c).
Example Sentence 2
While flying the published VFR corridor through the Class B, the crew reduced speed to 200 knots indicated to satisfy 14 CFR Part 91 — 91.117(c).