Which of the following speeds is specifically prohibited in Class Bravo while below 10,000 feet?

In Class Bravo airspace, pilots are required to adhere to specific speed restrictions to ensure safe separation and management of aircraft operations within busy terminal areas. One of the critical rules is that, while below 10,000 feet MSL (Mean Sea Level), no aircraft is allowed to exceed a speed of 250 knots indicated airspeed (KIAS) unless specifically authorized by air traffic control. This regulation helps maintain control and reduces the risk of overlapping flight patterns among the numerous aircraft operating in a congested environment, thereby enhancing safety.

The other speeds listed, such as 260 KIAS, 280 KIAS, and 300 KIAS, are all above this 250 KIAS threshold and would not be permitted without special clearance in Class Bravo airspace below 10,000 feet. Adhering to this speed limit is crucial for maintaining orderly air traffic operations in areas with high-density traffic and ensuring adequate wake turbulence separation among aircraft.

Thus, the correct answer highlights a specific regulation essential for flight safety in busy airspace.