Which of the following clearances includes the phrase 'AT THE PILOT'S DISCRETION'?

The phrase "AT THE PILOT'S DISCRETION" is often included in clearances that give pilots the authority to manage their altitude changes based on their own judgment. In this context, when a clearance is issued to climb or descend at the pilot's discretion, it signifies that the pilot can choose the timing and rate of ascent or descent as they see fit, rather than following a predetermined altitude or maneuver specified by Air Traffic Control (ATC).

This phrase emphasizes the pilot's authority and responsibility in decision-making during flight operations, particularly in terms of managing the aircraft's performance. It indicates that the pilot can navigate the altitude changes considering the conditions and situation at hand, ensuring safe operation while maintaining situational awareness.

The other options do not include this phrase typically because they involve more specific instructions where the pilot's discretion does not apply in the same way as it does with a climb or descent. For instance, clearances to the outer marker or for landing involve set procedures and specific guidance that pilots must follow closely.