11.03.05.04

.04 Obstruction Standards.

A. An obstruction is a hazard to air navigation if it:

(1) Is greater than 200 feet above ground level and within 3 nautical miles of the established reference point of any public-use airport licensed by the Administration; or

(2) Penetrates any imaginary surface specified in this regulation as applied to any airport.

B. For the purpose of this chapter, airport runways are classified as follows:

Table 1: Runway Classifications
Type of Runway Classification
Utility Runway:  
   Visual approaches only I
   With nonprecision instrument approach II
Runway with greater than utility capacity—visual approaches only III
Runway with greater than utility capacity and a nonprecision instrument
approach with visibility minimum greater than 3/4 statute mile
IV
Precision instrument approach or nonprecision approach and visibility
minimum of 3/4 statute mile or less
V
Precision instrument runway using an Instrument Landing System (ILS)
or a Precision Approach Radar (PAR)
VI

C. Imaginary Surfaces.

(1) Imaginary surfaces are various planes or curved surfaces constructed at specified angles or arcs in relation to an airport runway. They shall be determined separately for each airport and for each runway at that airport, depending on the classification of the runway and the most precise type of aircraft instrument approach available or planned for the runway.

(2) Because of the interrelationship of the imaginary surfaces, they shall be determined in the following sequence:

(a) Primary surface;

(b) Horizontal surface;

(c) Conical surface;

(d) Approach surface; and

(e) Transitional surface.

(3) When two surfaces overlap, the following apply:

(a) The primary surface takes precedence over any other surface;

(b) The approach surface takes precedence over the horizontal and conical surfaces to the extent the approach surface imposes a lower height limitation; and

(c) The transitional surface takes precedence over the horizontal surface.

D. Each imaginary surface shall be determined in the following manner:

(1) Primary Surface.

(a) The primary surface shall be longitudinally centered on the runway, at the runway elevation, and extend 200 feet beyond each end of the runway when the runway has a specifically prepared hard surface. In the absence of a hard surface, the ends of the primary surface shall coincide with the ends of the runway.

(b) The width of the primary surface shall be:

Runway Classification Width
I 250 feet
II, III, IV 500 feet
V, VI 1,000 feet

(c) The width of the primary surface shall be that width prescribed in this subsection for the most precise approach existing or planned for either end of the runway.

(2) Horizontal Surface.

(a) The horizontal surface is a horizontal plane 150 feet above the established airport elevation, the perimeter of which is determined by arcs of specified radius centered at each end of the primary surface connected by lines tangent to those arcs.

(b) The perimeter of the horizontal surface shall be determined by the following radii:

Runway Classification Radius
I, II, III 5,000 feet
IV, V, VI 10,000 feet

(c) When a 5,000-foot arc is encompassed by tangents connecting two adjacent 10,000-foot arcs, the 5,000-foot arc shall be disregarded in the construction of the perimeter of the horizontal surface.

(3) Conical Surface. The conical surface for all runway classifications extends outward and upward from the periphery of the horizontal surface at a slope of 20:1 for a horizontal distance of 4,000 feet.

(4) Approach Surface.

(a) The approach surface is longitudinally centered on the extended runway centerline and extends outward and upward from each end of the primary surface. The approach surfaces pass through and take precedence over the horizontal and conical surfaces.

(b) The length, width, and slope angle of the approach surface is specified in Table 2 for each runway classification.

(c) The approach surface is applied to each end of each runway at an airport based upon the type of approach available or planned for that runway end.

(5) Transitional Surface.

(a) The transitional surface extends outward and upward at right angles to the runway centerline and the runway centerline extended, at a slope of 7 to 1 from the sides of the primary surface and from the sides of the approach surfaces, to an elevation of 150 feet above the established airport elevation.

(b) For those portions of a precision approach surface that extend through the conical surface, the transitional surface extends at right angles to the runway centerline extended for a horizontal distance of 5,000 feet, measured from the edge of the approach surface.

E. To provide clearance for mobile objects operating on traverse ways on or near a public-use airport that does not have an operative ground traffic control service coordinated with the air traffic control service, the actual height of the traverse way shall be adjusted upwards by the following amounts:

Type of Traverse Way Increase in Height
Interstate highway 17 feet
Other public roadways 15 feet
Private roadways The greater of 10 feet or the height of the highest
mobile object that would normally use the roadway
Railroads 23 feet
Other traverse ways, including waterways The height of the highest mobile object that would
normally use the traverse way

Table 2: Dimensions of Approach Surface*
Runway Class Description Width of Inner Edge Width of Outer Edge Horizontal Length Slope Angle
I Utility runway; visual approaches only 250 ft. 1,250 ft. 5,000 ft. 20 to 1
II Utility runway; nonprecision approach 500 ft. 2,000 ft. 5,000 ft. 20 to 1
III Runway with greater than utility capacity;
visual approaches only
500 ft. 1,500 ft. 5,000 ft. 20 to 1
IV Runway with greater than utility capacity;
nonprecision approach with visibility minimums
greater than 3/4 statute mile
500 ft. 3,500 ft. 10,000 ft. 34 to 1
V Runway with greater than utility capacity;
nonprecision approach with visibility minimums
as low as 3/4 statute mile
1,000 ft. 4,000 ft. 10,000 ft. 34 to 1
VI Precision instrument runway using either an Instrument Landing System 1,000 ft. 16,000 ft. 10,000 ft. plus 40,000 ft. 50 to 1
  (ILS) or Precision Radar Approach (PAR)       40 to 1

* The inner edge of the approach surface is equal to, and abuts, the primary surface