Who is responsible for coordination when a high altitude controller requests a lower altitude for an aircraft over an adjacent sector?

The correct choice regarding the responsibility for coordination when a high altitude controller requests a lower altitude for an aircraft over an adjacent sector is the high altitude controller. This controller initiates the request for altitude change based on the aircraft's current flight path and any operational necessities. The high altitude controller holds the primary responsibility to ensure safe and efficient management of air traffic as it transitions altitude. By making the request, they are expected to provide necessary reasons and ensure that the adjacent sector controller is informed of the aircraft's intention and its implications on the traffic in that sector.

In air traffic control, effective communication and coordination are critical for maintaining safety among aircraft in different sectors. While the adjacent sector controller will certainly play a significant role in responding to the request and ensuring that clearance can be safely provided, the initial responsibility to coordinate such changes resides with the high altitude controller. Therefore, they act as the primary point of contact for such operational requests.