One of the most common questions that non-pilots ask is whether airplanes have to obey a speed limit like cars do. The answer, as with many things in life, is that it depends.
Aircraft operations are governed by the Federal Aviation Regulations, more commonly called the FARs. Aircraft speed limits are found in FAR 91.117, which spells out different speed limits for several different situations.
A common speed limit encountered by all airplanes is the restriction to fly at 250 knots (288 mph) or less when under an altitude of 10,000 feet. The vast majority of light general aviation airplanes cannot fly faster than 250 knots and most never go above 10,000 feet, but after every takeoff and before every landing jet pilots must make sure that they obey the speed limit. Above 10,000 feet, jets typically fly at faster airspeeds during cruise flight.
A second speed limit applies below 2,500 feet within four nautical miles of “of the primary airport of a Class C or Class D airspace area.” Class C or D airports are small to medium-sized airports with a control tower. If an airport has airline service, chances are good that it is a Class C or D airport. Many busy general aviation airports fall within these categories as well. The speed limit for these areas is 200 knots (230 mph).
A speed limit also applies beneath Class B airspace. Class B airspace surrounds major metropolitan airports in places like New York, Atlanta, Chicago, and Los Angeles. Class B airspace starts at the surface immediately surrounding the airport then goes higher as the distance from the airport increases. It is commonly described as an “upside down wedding cake.” When flying underneath the outer rings of Class B airspace, aircraft are restricted to 200 knots (230 mph). Aircraft flying through the Class B airspace, like airliners taking off and landing at the main airport, are not subject to the speed limit, but they do have to abide by the 250 knot speed limit below 10,000 feet.
A common misconception even among experienced pilots is that Class B airspace does not have a specific speed limit. Aircraft flying through the Class B airspace, like airliners taking off and landing at the main airport, are not subject to the speed limit, but they do have to abide by the 250 knot speed limit while they are below 10,000 feet.
Class B airspace typically extends from the surface to 10,000 but in some cases it goes higher. For example, in Atlanta the ceiling of the Class B airspace extends up to 12,500 feet. In Denver, where the airport elevation is 5,348 feet, the ceiling of the Class B airspace is 12,000 feet. If an aircraft is descending into the Class B airspace from above, there is no speed limit when it enters the Class B. It can maintain a higher cruising speed until it descends below 10,000 feet.
Outside of these specific instances, airplanes have a limiting “never exceed” speed. This is a speed that is determined by the aircraft manufacturer and is the maximum safe speed for the aircraft to fly. Above the never exceed speed, the aircraft may not be structurally sound, especially in turbulence or if maneuvered abruptly.
Other than these cases, pilots are free to fly their airplanes as fast as they will go and they usually do. At least until the air traffic controllers make them slow down for other traffic.