A specified fix identifiable to a pilot by NAVAIDs or visual reference to the ground is used for what purpose?

The specified fix that is identifiable by a pilot through navigation aids (NAVAIDs) or visual references is fundamental for establishing and maintaining the position of an aircraft. This capability allows pilots to accurately navigate along their intended flight path, ensuring they are where they expect to be. By recognizing these fixes, pilots can confirm their current location, assess any necessary adjustments to their flight plan, and maintain the intended route safely.

Using NAVAIDs or ground references is particularly critical when navigating in complex airspace, during approaches, or in adherence to air traffic control instructions. This position awareness is crucial for effective situational awareness and contributes to the overall safety of the flight, as it assists in avoiding obstacles and ensuring compliance with air traffic regulations.

The other options, while relevant to various aspects of flight management, do not specifically pertain to the immediate use of a fix for maintaining an aircraft's position. Establishing cruising altitude and determining the destination airport require broader context regarding flight planning and navigation strategy. Calculating fuel requirements relates to operational planning rather than on-the-fly navigation. Thus, option C is the most accurate representation of the role of a specified fix in flight operations.