What does 'X' instruct a pilot to do?

When a controller uses 'X' to instruct a pilot, the most accurate interpretation within the context provided is the clearance to cross at a specified point. This emphasizes an important aspect of air traffic control communication, where specificity in instructions is crucial for maintaining safety and order in airspace.

A clearance to cross at a specified point ensures that the pilot understands exactly where and when to execute the maneuver, which is essential for maintaining safe separation from other aircraft and for adhering to designated flight paths. This type of instruction is particularly important when a pilot is navigating around controlled airspace or near airports, where precise cross-reference points are necessary for safe operations.

In contrast, the other choices refer to different types of clearances that have distinct meanings in aviation. For example, a contact approach clearance allows a pilot to proceed visually to the runway and is more about navigation rather than crossing at a specified point. Clearances through to the outer marker pertain to instrument approaches and require a specific understanding of approach procedures, while a clearance to climb/descend relates to altitude adjustments rather than intersection crossings. Each of these instructions serves a different purpose in air traffic operations, but the instruction to cross at a specified point is particularly focused on maintaining safe and efficient traffic flow.