What does "Climb or descend at pilot's discretion" mean?

The phrase "Climb or descend at pilot's discretion" indicates that the pilot has the authority to decide when to initiate a climb or descent, based on their assessment of the current situation and any relevant conditions. This instruction typically implies that the air traffic control (ATC) has granted the pilot flexibility in altitude change, allowing them to act according to their judgment rather than being directed by ATC.

This autonomy can be particularly useful in situations where a pilot may need to react to changing circumstances, such as weather conditions or traffic avoidance. Therefore, the pilot is empowered to determine the timing of the climb or descent, ensuring a balance between maintaining safety and following good airmanship practices.

The other options reflect restrictions that are not inherent in the phrase. For example, the requirement to always consult ATC or only change altitude in emergencies would limit the flexibility intended by the phrase, while following ATC instructions regardless of conditions contradicts the discretionary nature of the action.