For IFR aircraft in uncontrolled airspace and below 18,000 feet, what cruising altitude should they fly at from 0-179 degrees?

For IFR (Instrument Flight Rules) aircraft operating in uncontrolled airspace below 18,000 feet, the altitude regulation is designed to provide safe vertical separation between aircraft. Specifically, aircraft are expected to adhere to specific altitudes based on their magnetic course.

When an aircraft is flying on a magnetic course from 0 to 179 degrees, it is assigned to fly at odd thousand foot intervals. This means that they should operate at altitudes such as 3,000 feet, 5,000 feet, 7,000 feet, and so forth, all the way up to but not including 18,000 feet. This system is referred to as the "odd/even altitude rule" and helps in maintaining vertical separation among IFR traffic in such airspace.

This rule assists in reducing the risk of mid-air collisions and enhances the overall safety of air traffic management. The assignment of even thousand foot intervals to aircraft flying at a magnetic course from 180 to 359 degrees complements this system.