Which scenario requires immediate action from the pilot regarding altitude adjustment?

Immediate action regarding altitude adjustment is required when air traffic control requests a change. This is critical for maintaining safe and orderly air traffic. Air traffic controllers provide instructions to manage the flow of aircraft, ensuring that they are safely separated from one another, especially in busy airspace or during approaches and departures. Pilots are taught to prioritize these instructions as they are central to air safety and compliance with regulations.

In scenarios like nearing a destination, flying over mountains, or during cruise flight, altitude adjustments may be necessary but are often more routine or can be planned in advance rather than requiring immediate action. The distinction lies in the direct directive from air traffic control, which must be followed promptly to ensure safety and maintain effective communication with the control tower.