Chapter 3
Table 3.7. Airspace Imaginary Surfaces.
Class A Runway
Class B
Requirement
Runway
Item
Item
Requirement
No.
Description
Legend
VFR
IFR
VFR & IFR
Remarks
H
7:1
Slope ratio is
30
Slope of
horizontal:vertical.
Transitional
Surfaces
7:1 is 7 meters [feet]
horizontal to 1 meter [foot]
vertical.
Vertical height of vegetation
and other fixed or mobile
obstacles and/or structures
will not penetrate the
transitional surface. Taxiing
aircraft are exempt from this
requirement. For Navy and
Marine Corps airfields,
taxiway pavements are
exempt from this requirement.
For USAF, ATCT is exempt
from this requirement if the
height will not affect TERPS
criteria.
Notes:
1. Approach-Departure Surfaces are based on Instrument Approach-Departure procedures. Verify Instrument
Approach-Departure procedures with Army Aeronautical Service Agency, Air Force Flight Standard Agency or
Navy Flight Information Group (NAFIG), as appropriate, prior to using this table.
2. NA = Not Applicable
3. Airfield and heliport imaginary surfaces and safe wingtip clearance dimensions are shown as a direct
conversion from inch-pound to SI units.
3.14. Airspace for Airfields with Two or More Runways. Typical airspace requirements for an
airfield with multiple runways, such as a VFR and an IFR runway are shown in Figure 3.19.
3.15. Obstructions to Air Navigation. An existing object (including a mobile object) is, and a future
object would be, an obstruction to air navigation if it is higher than any of the the heights or surfaces
listed in Federal Aviation Regulations Part 77, Objects Affecting Navigable Airspace, and the surfaces
described in this manual.
3.15.1. Aircraft Movement Area. No part of the aircraft movement area itself will be considered an
obstruction if applicable grading criteria are met. (See the glossary for the definition of the Aircraft
Movement Area, as used in this manual.)
3.15.2. Determining Obstructions. For airfields located in the United States and trust territories, an
obstruction to air navigation is determined in accordance with the standards contained in Federal
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