What must be ensured before exceeding 250 KIAS below 10,000 feet MSL outside US sovereign airspace?

The correct choice emphasizes the necessity of adhering to mission requirements and conducting operations specifically in international airspace before exceeding 250 knots indicated airspeed (KIAS) below 10,000 feet mean sea level (MSL). This rule exists primarily for safety and regulatory compliance, as the limit is designed to help manage the risk of mid-air collisions, especially in busy airspace where the risk is heightened.

In international airspace, there may be different regulations or less restrictive conditions compared to domestic airspace, allowing for greater flexibility in speed. Therefore, if the mission requirements dictate the need to exceed this speed and the operations are explicitly taking place in international airspace, the pilots are authorized to do so because that context justifies it.

Understanding the operational environment and the specific mission parameters plays a crucial role in compliance with airspeed regulations. In contrast, other choices do not capture the specific need to operate under the specific conditions or contexts that necessitate a speed variance, which is critical for legal and operational safety.