At what vertical altitude does the speed limit of 250 KIAS apply?

The speed limit of 250 knots indicated airspeed (KIAS) applies below 10,000 feet altitude in controlled airspace. This standard is in place to minimize the risk of midair collisions in congested airspace, where many aircraft are operating at lower altitudes. It ensures that aircraft maintain a manageable speed as they approach airports or maneuver through busy air traffic regions.

Once above this altitude, the speed limit no longer applies, allowing pilots to operate at higher speeds, which is particularly useful for commercial and high-performance aircraft that are designed to fly efficiently at those altitudes. Therefore, the correct answer is that the speed limit of 250 KIAS applies at 10,000 feet.