Definition
Areas of terrain that do not meet the FAA's mountainous designation, where instrument procedure designers apply a minimum required obstacle clearance of 1,000 feet above the highest obstacle within the specified area. Non-mountainous areas are those not listed as mountainous in 14 CFR Part 95.
Plain English
Flatter or rolling terrain — anything not officially designated as mountainous — where instrument procedures only need to keep aircraft 1,000 feet above the tallest obstacle, rather than the larger margin used over mountains.
Context Anchor
Seen in instrument procedure design discussions, especially where required obstacle clearance changes depending on whether terrain is classified as mountainous or non-mountainous.
Why Pilots Care
The classification directly affects required obstacle clearance values and the resulting published altitudes on approach charts.
Grounding Statement
An area can have hills or tall obstacles and still be treated as a non-mountainous area if it is not in the FAA’s designated mountainous terrain category.
Intuition Check
Do not read non-mountainous as “flat” or “free of obstacles.” Here it means “not classified by the FAA as mountainous for the design rules being used.”
Example Sentence 1
Because the route ran through non-mountainous areas, the required obstacle clearance was 1,000 feet above the highest obstacle.
Example Sentence 2
Pilots receive lower published minimums when operating in non-mountainous areas compared with routes over classified mountainous terrain.