Definition
A descent gradient expressing how many feet of altitude an aircraft must lose for every nautical mile of horizontal distance flown along the approach course. On an Airport Surveillance Radar (ASR) approach, 150 feet per mile is the maximum descent gradient permitted between the final approach fix and the runway or missed approach point.
Plain English
It means the airplane is allowed to come down no faster than 150 feet of altitude for every mile it travels forward along the approach. Steeper than that is not permitted on this kind of approach.
Context Anchor
Seen in instrument approach material, including ASR approach discussions, when describing how quickly altitude changes along a flight path.
Why Pilots Care
Allows safe descent while maintaining required obstacle clearance during radar-guided approaches.
Grounding Statement
If you flew 3 nautical miles along a 150 feet per mile descent path, you would lose about 450 feet of altitude.
Intuition Check
Do not read “150 feet per mile” as a rate of descent. It is distance-based: altitude change per mile traveled, not altitude change per minute.
Example Sentence 1
The approach designer kept the final segment within 150 feet per mile so the procedure could be flown as a standard ASR approach.
Example Sentence 2
A 150 feet per mile gradient keeps the aircraft above terrain in the initial approach segment.