Which of the following must be confirmed before altering the aircraft's speed?

The requirement to confirm approval from the transferring controller and any necessary validations before altering an aircraft's speed emphasizes the importance of coordinated communication and collaboration in air traffic control. In the air traffic management system, controllers are responsible for maintaining safe separation between aircraft and ensuring that all operations are compliant with established procedures and regulations.

When an aircraft is en route, any changes, including speed adjustments, should be coordinated with the previous controller if the aircraft is transitioning between sectors or jurisdictions. This helps to ensure a smooth and safe handover of responsibility from one controller to another, reducing the risk of miscommunication and potential safety issues. Additionally, certain validations may include verifying that changes adhere to air traffic control regulations, available airspace, and any other operational constraints.

While reviewing the flight's previous speed, checking with the pilot for confirmation, and writing a new flight log are important tasks in the management of an air traffic scenario, they do not carry the same critical need for immediate regulatory compliance and safety assurance as receiving prior approval from the transferring controller does. Thus, confirming with the controller and any necessary validations is the most crucial step before making speed alterations for the safe operation of the flight.