What is the minimum IFR altitude over mountainous terrain?

The minimum IFR altitude over mountainous terrain is established to ensure a safe margin above obstacles and to provide adequate clearance over the highest terrain features. The standard minimum altitude prescribed is 2,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the centerline of the route being flown. This altitude is specifically designed to account for the complexities and hazards presented by mountainous areas, where terrain can rise sharply and may pose significant risks to aircraft operations.

The selection of 2,000 feet as the minimum IFR altitude reflects the need for an increased safety buffer. In contrast, lower altitudes, such as 1,000 feet, may not provide sufficient clearance, particularly in unpredictable or rapidly changing mountainous environments. Thus, operating at a minimum of 2,000 feet helps to ensure safe navigation and enhances the ability to respond to emergencies or in-flight issues by allowing for adequate altitude to maneuver.