Definition
The standard climb gradient required on a departure procedure when no higher gradient is published. Expressed as 48 feet of altitude gained per nautical mile of horizontal distance flown over the ground, it is the minimum climb performance the FAA assumes for obstacle clearance on a standard instrument departure.
Plain English
It means the aircraft must climb at least 48 feet for every nautical mile it travels forward. If you fly one nautical mile, you must be at least 48 feet higher than where you started.
Context Anchor
Seen in instrument procedure design criteria, especially when explaining how standard departure climb requirements create obstacle clearance after takeoff.
Derivation
The unit combines feet (vertical distance) with NM, the abbreviation for nautical mile (horizontal distance). Reading it as 'feet per nautical mile' makes the relationship clear: a measure of how steeply the aircraft is climbing relative to the ground covered.
Why Pilots Care
Specifies the exact vertical performance needed to maintain obstacle clearance during a procedure segment.
Grounding Statement
Picture two rising lines after takeoff: the airplane’s expected climb line rises faster than the protected obstacle line, and the gap between them grows by 48 feet each nautical mile.
Intuition Check
Do not read 48 ft/NM as an airspeed or a vertical speed in feet per minute. It is a slope: feet of height gained for each nautical mile traveled across the ground.
Example Sentence 1
Unless a higher gradient is published, the standard departure design assumes the aircraft can climb at 48 ft/NM.
Example Sentence 2
Procedure designers apply a 48 ft/NM gradient when calculating required performance for certain initial approach segments.