germb747
Well-Known Member
If I recall correctly, I think an airport has to have certain weather reporting capability to call itself Class D. Certainly muddies the waters though.
Class D
- Thread starter popaviator
- Start date
If I recall correctly, I think an airport has to have certain weather reporting capability to call itself Class D. Certainly muddies the waters though.
tgrayson
New Member
The actual document that defines the airspace dimensions is FAAO 7400-9E. The formula that popaviator uses comes from FAA 7400.2, Procedures for Handling Airspace Matters, and *may* have been used as a basis for determining the airspace dimensions in the .9E document, but there are other considerations, too. Here is the relevant section:
17-2-5. DETERMINING CLASS D AREA SIZE
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).
NOTE-
Normally, the person responsible for developing instrument procedures for civil and U.S. Army airports is a FAA Aviation Standards Airspace Evaluation Specialist. A military representative handles all other military procedures.
17-2-6. DEPARTURES
a. 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).
b. 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.
c. In areas with rising terrain, apply the procedures reflected in FIG 17-2-2.
17-2-7. ARRIVAL EXTENSION
a. A Class D area arrival extension shall 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.
b. When multiple approach procedures are established using the same initial approach course, but with different 1,000-foot points, the extension length shall 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 shall coordinate with the person responsible for developing the instrument approach to request the adjustment.
c. The width of the extension shall 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 shall be used for the extension. These extensions shall, in all cases, extend to a minimum of 1 NM on each side of the centerline.
d. 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.
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).
NOTE-
Normally, the person responsible for developing instrument procedures for civil and U.S. Army airports is a FAA Aviation Standards Airspace Evaluation Specialist. A military representative handles all other military procedures.
17-2-6. DEPARTURES
a. 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).
b. 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.
c. In areas with rising terrain, apply the procedures reflected in FIG 17-2-2.
17-2-7. ARRIVAL EXTENSION
a. A Class D area arrival extension shall 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.
b. When multiple approach procedures are established using the same initial approach course, but with different 1,000-foot points, the extension length shall 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 shall coordinate with the person responsible for developing the instrument approach to request the adjustment.
c. The width of the extension shall 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 shall be used for the extension. These extensions shall, in all cases, extend to a minimum of 1 NM on each side of the centerline.
d. 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.
Please tell me you're joking.
Don't take this the wrong way, but why would that be important for a pilot to know?
-mini
popaviator
Well-Known Member
I don't know... The more private Chinese students I teach the more I feel the need to challenge my students. Plus, they can grasp formulas pretty easily.
:yeahthat: I'll tell students that Class D is generally 5sm radius and up to 2500 AGL, because that's a question they could expect on a written or oral, but I'll also tell them that there are a heck of a lot of exceptions to that, and the best way to make sure of the size of the Class D you're flying into is to look at the chart. There are a LOT of oddly-sized Class Ds in the area (different radii, extensions, etc.), so just going by the general rule won't work here.
But what have they really learned by learning the formula? They'd have to find the ARP, which you might be able to derive to a fair degree of accuracy by looking at the airport diagram or the airport sketch in the A/FD and translate over to the sectional chart, but since the dimensions are shown on the sectional chart anyway, what have you really accomplished?
If you wanted something to challenge them, I'd use the stuff that tgrayson posted, and use it to describe why it is that some Class Ds are differently shaped than others, just as a "nice to know" sort of thing.
BillErvin
Peddling as fast as I can
What is the size of this class D
Not as rare as you think, I can think of two in the Dallas area that up until a couple of months ago were G airspace with towers, and another that went Delta awhile back. All three were within 20 miles of each other
germb747
Well-Known Member
How did they calculate Redbird(Dallas Executive for you youngsters)
They took 2.5 times the square root of Pi, divided by the cosine of theta, then plugged it into this formula (which will be asked on your commercial pilot oral)
:
Then again, maybe they just kind of followed that road to the west of the airport :bandit:
amjon
Pilot and A Half (for now
Some guy liked the drawing his kid made and said, "Hey, that would make a cool airspace!"
How did they calculate Redbird
CoffeeIcePapers
Well-Hung Member
The ARP is listed at the top of the AFD page for the airport.
The ARP is at the Lat/Long listed at the end of the first line.
So in the situation of a towered airport in Class G, I know that you have to treat it the same way you would a Class D as far as communications go (you must talk to them). But I couldn't find anything on weather requirements, which leads me to believe that you can fly around that airport with 1sm visibility and clear of clouds as long as you're talking to the tower. Is that true, or am I missing something?
CoffeeIcePapers
Well-Hung Member
Class G is Class G.
germb747
Well-Known Member
§ 91.126 Operating on or in the vicinity of an airport in Class G airspace.
(a) General. Unless otherwise authorized or required, each person operating an aircraft on or in the vicinity of an airport in a Class G airspace area must comply with the requirements of this section.
(b) Direction of turns. When approaching to land at an airport without an operating control tower in Class G airspace—
(1) Each pilot of an airplane must make all turns of that airplane to the left unless the airport displays approved light signals or visual markings indicating that turns should be made to the right, in which case the pilot must make all turns to the right; and
(2) Each pilot of a helicopter or a powered parachute must avoid the flow of fixed-wing aircraft.
(c) Flap settings. Except when necessary for training or certification, the pilot in command of a civil turbojet-powered aircraft must use, as a final flap setting, the minimum certificated landing flap setting set forth in the approved performance information in the Airplane Flight Manual for the applicable conditions. However, each pilot in command has the final authority and responsibility for the safe operation of the pilot's airplane, and may use a different flap setting for that airplane if the pilot determines that it is necessary in the interest of safety.
(d) Communications with control towers. Unless otherwise authorized or required by ATC, no person may operate an aircraft to, from, through, or on an airport having an operational control tower unless two-way radio communications are maintained between that aircraft and the control tower. Communications must be established prior to 4 nautical miles from the airport, up to and including 2,500 feet AGL. However, if the aircraft radio fails in flight, the pilot in command may operate that aircraft and land if weather conditions are at or above basic VFR weather minimums, visual contact with the tower is maintained, and a clearance to land is received. If the aircraft radio fails while in flight under IFR, the pilot must comply with §91.185.
[Doc. No. 24458, 56 FR 65658, Dec. 17, 1991, as amended by Amdt. 91–239, 59 FR 11693, Mar. 11, 1994; Amdt. 91–282, 69 FR 44880, July 27, 2004]
