What is the maximum allowable airspeed for pilots below 10,000 feet MSL?

The maximum allowable airspeed for pilots operating below 10,000 feet Mean Sea Level (MSL) is 250 knots. This regulation is in place to help ensure safety in busy airspaces, often around airports, where a lower speed helps to manage traffic and reduce the risk of collisions. This speed limit is part of the Federal Aviation Administration (FAA) regulations and is aimed at ensuring a streamlined flow of air traffic as well as reducing the likelihood of wake turbulence incidents, which can occur at higher speeds.

In contrast, other airspeeds listed do not apply within this altitude range. A speed of 200 knots is too low and not a standard limit for this altitude; 300 knots is above the maximum limit, and 150 knots is also not applicable as it is below the stipulated speed. Thus, the correct answer is grounded in the regulations that pilots must follow to ensure safe operations below 10,000 feet.