What minimum speed may ATC request of a turbine-powered aircraft operating below 10,000 feet?

Answer: B — 210 knots.

In the context of air traffic control regulations, when dealing with turbine-powered aircraft operating below 10,000 feet, the minimum speed ATC can typically request is 250 knots. This standard applies to most jet and turboprop aircraft, establishing a clear guideline for managing traffic flow and ensuring safety in congested airspace. While 180 knots is often mentioned as a minimum speed for certain operations, particularly for slower general aviation aircraft, turbine-powered aircraft have a different operational profile that calls for a higher minimum speed. The speeds of 200 and 210 knots are not standard for turbine-powered operations, making them less applicable in this scenario. Thus, a request of 250 knots aligns with established air traffic control procedures for ensuring that turbine-powered aircraft maintain adequate separation from slower aircraft and operate effectively within the busy lower airspace. This requirement ensures that air traffic controllers can manage safely and efficiently the various types of aircraft in their vicinity.