Definition
An imaginary sloping surface used by procedure designers to identify obstacles in the final approach segment of a non-precision instrument approach. The surface rises one foot vertically for every 34 feet horizontally, extending outward from the runway threshold along the final approach course. Any obstacle penetrating this surface must be evaluated and, if not removed, accounted for by raising the minimum descent altitude or adjusting the procedure.
Plain English
A gently sloped imaginary ramp the FAA draws out from the end of the runway. If a tree, tower, or building pokes up through that ramp, the approach has to be designed with higher minimums to keep aircraft safely above it.
Context Anchor
You may encounter this term in FAA instrument procedure design discussions, especially where the handbook explains how obstacles are evaluated near the runway during the final approach segment.
Derivation
The 34:1 refers to the slope ratio: 34 feet horizontal for every 1 foot vertical, a roughly 1.7-degree climb. This gentle slope reflects the shallow descent path typical of a non-precision final approach.
Why Pilots Care
Any obstacle that breaks through this surface may force a higher minimum altitude or additional restrictions, directly affecting whether the approach can be flown safely in instrument conditions.
Analogy
Think of an invisible, shallow sheet extending out from the runway area. If a tower or hill pokes through that sheet, procedure designers have to account for it.
Grounding Statement
Picture a long, gentle ramp starting near the runway and tilting upward at a shallow angle; anything poking above it gets flagged.
Intuition Check
A “surface” here is not pavement and not something the airplane lands on; it is an imaginary plane used for obstacle evaluation. “34:1” is not an instruction to fly that exact slope; it is the slope used to identify obstacles.
Example Sentence 1
A new cell tower built off the approach end of Runway 18 penetrated the 34:1 final approach obstacle identification surface, forcing an amendment to the published MDA.
Example Sentence 2
A new tower was found to penetrate the 34:1 final approach obstacle identification surfaces, requiring an adjustment to the published altitudes.