Section 2. Class D Airspace Standards
- A Class D airspace area must be of sufficient size to:
- Allow for safe and efficient handling of operations.
- Contain IFR arrival operations while between the surface and 1,000 feet above the surface and IFR departure operations while between the surface and the base of adjacent controlled airspace.
- Size and shape may vary to provide for 1 and 2 above. The emphasis is that a Class D area must be sized to contain the intended operations.
- The Class D airspace boundary should normally be based on the airport reference point (ARP) or the geographic position (GP) of the primary airport. The ARP/GP is the center of the airport expressed in coordinates and should be incorporated into the surface area's legal description.
- If a Class E surface area is established in conjunction with a part-time Class D area, the areas should normally be coincident. Explain any differences in the rulemaking documents.
Under certain conditions, the ARP/GP can change. If this occurs, the airspace should be reviewed to ensure the instrument procedures are still contained within existing airspace.
- Using shelves and/or cutouts to the extent practicable, exclude satellite airports from the Class D airspace area (see FIG 17-2-3).
- Satellite airports within arrival extensions may be excluded using the actual dimensions of the TERPs trapezoid.
- Do not exclude airports inside the TERPs primary obstruction clearance area of the procedure(s) for which the surface area is being constructed or when the exclusion would adversely affect IFR operations.
Designate separate Class D airspace area for airports in proximity to each other. A common boundary line must be used so that the airspace areas do not overlap. When operationally advantageous, the common boundary separating adjacent Class D areas may be eliminated if the areas are contained in an existing Class B or Class C airspace area controlled by the same IFR ATC facility.
The size of a Class D area, and any necessary extensions, is determined by the use of a 200 feet per NM climb gradient and information obtained from the person responsible for developing instrument procedures (see FIG 17-2-1).
- When diverse departures are authorized, design the Class D area using a radius of 3.5 NM plus the distance from the ARP/GP to the departure end of the outermost runway (see FIG 17-2-1).
- When specific departure routes are required, the routes will determine the shape of the Class D area. Use the 200 feet per NM climb gradient procedure in subparagraph a. above and FIG 17-2-2 plus 1.8 NM either side of the track(s) to be flown.
- In areas with rising terrain, apply the procedures reflected in FIG 17-2-2.
- A Class D area arrival extension must be established to the point where an IFR flight on an instrument approach can be expected to descend to less than 1,000 feet above the surface.
- When multiple approach procedures are established using the same initial approach course, but with different 1,000-foot points, the extension length must be based on the approach requiring the greatest distance. Consistent with safety and operational feasibility, if an adjustment to the 1,000-foot point can be made to eliminate or shorten an extension, the specialist must coordinate with the person responsible for developing the instrument approach to request the adjustment.
- The width of the extension must be equal to the width of the TERPs primary obstruction clearance area at the point where an IFR flight on an instrument approach can be expected to descend to an altitude below 1,000 feet above the surface. However, if the primary area widens between the point where the flight leaves 1,000 feet and the airport, the widened portion of the primary area located outside the basic surface area radius must be used for the extension. These extensions must, in all cases, extend to a minimum of 1 NM on each side of the centerline.
- If all arrival extensions are 2 NM or less, they will remain part of the basic Class D area. However, if any extension is greater than 2 NM, then all extensions will be Class E airspace.
Class D areas should normally extend upward from the surface up to and including 2,500 feet AGL. The altitude must be converted to MSL and rounded to the nearest 100 feet. However, in a low density or non-turbo aircraft traffic environment, a vertical limit of 2,500 feet AGL may be excessive and a lower altitude should be used.
The nearest 100 feet means that 49 feet and below must be rounded down and 50 feet and above must be rounded up.
Communications capability must exist with aircraft, that normally operate within the Class D Surface Area down to the runway surface of the primary airport (the airport upon which the surface area is designated). This communication may be either direct from the ATC facility having jurisdiction over the area or by rapid relay through other communications facilities which are acceptable to the ATC facility having that jurisdiction.
- Weather observations must be taken at the primary airport during the times and dates the Class D airspace is active. A federally certified weather observer or a federally commissioned automated weather observing system (this includes all FAA and NWS approved and certified weather reporting systems) can take the weather observation. The weather observer must take routine (hourly) and special observations. An automated weather observing system can provide continuous weather observations.
- Scheduled record and special observations from weather observers or automated weather reporting systems must be made available to the ATC facility(s) having control jurisdiction over the Class D designated surface area. This can be accomplished through Flight Service Station (FSS), Longline Dissemination, National Weather Service (NWS), or other FAA-approved sources. Facilities that require weather reports from satellite airports may enter into a letter of agreement (LOA) with the associated FSS, airline/contract observer, airport management, etc.
- At ATC sites where non-Federal employees perform weather duties, the appropriate FAA office must ensure that the reporting and dissemination requirements applicable to National Weather Service and FAA publication standards are followed.
- In facilities where direct access to automated weather observing systems is not available, controllers will apply the provisions of FAA Order JO 7110.65, Air Traffic Control.
- If the capabilities outlined in paragraph 17-2-9 and/or paragraph 17-2-10 are temporarily out of service for an active Class D Surface Area, a Notice to Air Missions must be issued stating the temporary loss of the affected service.
- However, if it is determined that the capabilities are consistently unavailable, a Notice to Air Missions must be issued, as described above, and rulemaking action initiated to revoke the Surface Area, as appropriate.
- The FPT needs to be kept informed of any planned action, especially when instrument approach procedures (IAP) are involved, so as to assess the impact on published approaches. The Standards Specialist may decide changes are needed in the IAP, dependent on possible new altimeter source and other considerations. These changes will have an effect on the airspace action required; for example, minimums may be raised, or procedure may be canceled.
Class D AREA RADIUS FORMULA
ARP/GP = AIRPORT REFERENCE POINT AND/OR GEOGRAPHIC POSITION
EOR = END OF OUTERMOST RUNWAY
6076 = ONE NAUTICAL MILE IN FEET
200 FEET PER NAUTICAL MILE = STANDARD CLIMB GRADIENT
D = DISTANCE IN FEET FROM ARP/GP TO EOR 3.5 MILES = DISTANCE
REQUIRED FOR DEPARTURE TO REACH 700-FOOT CLASS E AIRSPACE USING STANDARD CLIMB GRADIENT
2.5 MILES = DISTANCE REQUIRED FOR DEPARTURE TO REACH 1200-FOOT
CLASS E AIRSPACE USING STANDARD CLIMB GRADIENT
((1200 - 700)/200)
THE FORMULA CAN BE EXPRESSED AS: R = D/6076 + 3.5
At Airport A, the distance from the geographic position to the end of the outermost runway
is 4,023 feet; therefore, assuming flat terrain, the radius is calculated as:
R = 4023/6076 + 3.5 = .662 + 3.5 = 4.162 = 4.2
The radius for the 700-foot Class E airspace becomes: 4.2 + 2.5 = 6.7
In the above example, an aircraft departing to the west would reach the lateral boundary of the surface area without reaching 700 feet AGL and, in effect, leave controlled airspace. To ensure that the lateral boundary of the Class D area is congruent with the beginning of the 700-foot Class E airspace, the specialist must:
- Search the Class D area's radius circle for the highest terrain.
- Calculate the MSL height of the aircraft by adding 700 feet to the airport elevation.
Compare MSL altitudes of the aircraft versus the highest terrain to determine if the
aircraft has reached the overlying or adjacent controlled airspace. If not, increase the size
of the Class D area, as necessary, to contain the departure.
When terrain, obstacles, or procedures prohibit departures in portions of the basic surface area, a terrain search is not necessary in that area and that height is not used in the computations.