When can you change your assigned speed of 210 KIAS while being vectored for an approach?

Changing your assigned speed while being vectored for an approach is governed by air traffic control (ATC) procedures. The correct option emphasizes that the pilot can adjust their speed when they are cleared for an approach or given a new speed instruction by ATC. This is crucial for maintaining safe separation between aircraft and ensuring efficient workflow during approach sequences.

When ATC provides clearance for an approach or issues a new speed assignment, it signals to the pilot that modifications to flight parameters are allowed. Prioritizing safety and coordination, ATC manages the traffic flow and spacing between aircraft during critical phases of flight such as approaches.

The other options do not accurately reflect the operational procedures. For example, changing the speed immediately without ATC clearance could lead to miscommunication or separation issues, and waiting until reaching a specific altitude such as 4,000 feet does not align with ATC directives in the approach context. Thus, the correct approach is to rely on ATC guidance to ensure compliance with air traffic regulations.