The pilot in command of an aircraft operated under IFR, in controlled airspace, not in radar contact, shall report by radio as soon as possible when?

The correct answer is that the pilot in command operating under IFR in controlled airspace, not in radar contact, should report by radio as soon as possible when passing each designated reporting point, including time and altitude. This requirement ensures that air traffic control (ATC) remains aware of the aircraft's position, which is critical for maintaining safe separation between aircraft, especially in controlled airspace where traffic can be dense. Reporting at designated points provides ATC with essential information to monitor the progress of aircraft and manage air traffic efficiently.

In the context of IFR operations, designated reporting points serve as reference locations that can be used for navigation and traffic management. By providing updates on their altitude and time when passing these points, pilots assist ATC in maintaining situational awareness and facilitating safe operations.

The other options, while relevant in different contexts, do not pertain specifically to the requirement of reporting position in the manner that designated reporting points do. For instance, while crossing FL 180, changing control facilities, or entering a holding pattern all involve communication with ATC, they do not carry the same routine necessity for position reporting as passing designated points does within controlled airspace without radar contact.