What does the X signify on a Low en route chart?

The presence of an “X” on a Low Enroute chart indicates a computer navigation fix or a mileage break. These marks serve an important purpose in navigation, allowing pilots to identify specific points along their route that are significant for both planning and position reporting. When flying under instrument flight rules (IFR), these fixes are used to ensure precise navigation and to assist with compliance to air traffic control instructions.

The “X” helps define the boundaries between segments of airways and indicates where distance measurement is made, contributing to route management. This format is particularly useful for pilots when calculating estimated times of arrival or distances to go, ensuring a smooth transition from one phase of flight to another. Understanding how these markers function is critical for maintaining situational awareness in the cockpit.