What altitude should IFR aircraft in controlled airspace fly at?

In controlled airspace, IFR (Instrument Flight Rules) aircraft are required to fly at altitudes assigned by Air Traffic Control (ATC). This ensures that aircraft are safely separated from one another based on their assigned altitudes, which is critical for maintaining safety and efficiency in busy airspace. ATC has the responsibility to manage air traffic and make adjustments as necessary for safety, traffic flow, and to accommodate other factors such as weather.

While odd and even thousand-foot intervals are standard practices for altitude assignment (typically used for VFR - Visual Flight Rules), IFR aircraft may not necessarily follow this pattern if ATC has assigned a specific altitude that may fall outside of those standard intervals. Additionally, Flight Level 180 is a specific altitude that applies to certain airspace in terms of separation, but it’s not the general requirement for all IFR flights. Therefore, the correct approach is to follow the altitudes assigned by ATC, which can vary depending on the situation and traffic.