Federal Aviation Act, Title 14, Part 77
FAA Regulation Title 14 Part 77, commonly known as Part 77, provides the
basis for evaluation of vertical obstruction compatibility. This regulation
determines compatibility based on the height of proposed structures or
natural features in relation to their distance from the ends of a runway.
Using the distance formula from this regulation, local jurisdictions can easily
assess height restrictions near airfields.
The surface of a takeoff and landing area of a civilian airport or any
imaginary surface established under 77.19, DOD: 77.21, and heliports:
77.23. However, no part of the takeoff or landing area itself will be
considered an obstruction.
Except for traverse ways on or near an airport with an operative
ground traffic control service furnished by an airport traffic control
tower or by the airport management and coordinated with the air
traffic control service, the standards of paragraph (a) of this section
apply to traverse ways used or to be used for the passage of mobile
objects only after the heights of these traverse ways are increased by:
Additional information on Part 77 is located on the Federal Aviation
Administration Internet site at http://www.faa.gov/.
As of January 29, 2013, the main focus of Part 77.17 is to establish standards
to determine obstructions within navigable airspace, typically within a
certain distance from an airport or airfield. It defines an obstruction to air
navigation as an object that is of greater height than any of the following
heights or surfaces in the following manner:
A height of 499 feet AGL at the site of the object.
A height that is 200 feet AGL or above the established airport
elevation, whichever is higher, within 3 nautical miles of the
established reference point of an airport, excluding heliports, with its
longest runway more than 3,200 feet in actual length. This height
increases in the proportion of 100 feet for each additional nautical
mile of distance from the airport up to a maximum of 499 feet.
A height within a terminal obstacle clearance area, including an initial
approach segment, a departure area, and a circling approach area,
which would result in the vertical distance between any point on the
object and an established minimum instrument flight altitude within
that area or segment to be less than the required obstacle clearance.
A height within an enroute obstacle clearance area, including turn and
termination areas, of a federal airway or approved off‐airway route
that would increase the minimum obstacle clearance altitude.
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17 feet for an Interstate Highway that is part of the National
System of Military and Interstate Highways where
overcrossings are designed for a minimum of 17 feet vertical
distance.
15 feet for any other public roadway.
10 feet or the height of the highest mobile object that would
normally traverse the road, whichever is greater, for a private
road.
23 feet for a railroad.
For a waterway or any other traverse way not previously
mentioned, an amount equal to the height of the highest
mobile object that would normally traverse it.
The FAA has also identified certain imaginary surfaces around runways that
are used to determine how structures and facilities are evaluated. The
levels of imaginary surfaces build upon one another and are designed to
eliminate obstructions to air navigation and operations, either natural or
man‐made. The dimension or size of an imaginary surface depends on the
runway classification.
Background Report
June 2017