Aviation Theory

pages: 1: Airspace types, Class A | 2: Class B to E | 3: Special Airspace Use

SPECIAL VFR

You may conduct normal VFR operations such as traffic pattern entry, takeoffs, or landings below 10,000 feet MSL within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport. You may obtain an ATC clearance for special VFR during the day if the visibility is at least one mile and you can remain clear of clouds. Special VFR is not permitted between sunset and sunrise unless you have a current instrument rating and the aircraft is equipped for instrument flight. In addition, special VFR clearances are not issued to fixed-wing aircraft (day or night) at the nation's busier airports which are listed in Section 3 of Appendix D of FAR 91. Figure 1-3 lists a summary of each class of airspace.

* Different visibility minima and distance from cloud requirements exist for operations above 10,000 feet MSL.

** Different visibility minima and distance from cloud requirements exist for night operations, operations above 10,000 feet MSL, and operations below 1,200 feet AGL.

Note: Two-way radio communications are required for all operations where temporary or non-federal control towers are established and operating within Class E and G airspace. Refer to FARs 91.126 and 91.127.

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AIRCRAFT SPEED LIMITS

Unless otherwise authorized by air traffic control or exceptions to the regulations, you may not operate an aircraft below 10,000 feet MSL at a speed greater than 250 knots indicated airspeed (KIAS). Further, unless otherwise authorized or required by ATC, you may not operate an aircraft at or below 2,500 feet above the surface within four nautical miles of the primary airport of a Class C or Class D airspace area at a speed greater than 200 KIAS. The 200 KIAS limit also applies to the airspace underlying a Class B airspace or in a VFR corridor designated through such airspace.

SPECIAL USE AIRSPACE

Other segments of airspace, both controlled and uncontrolled, have been designated as special use airspace. Activities conducted within these areas are considered hazardous to civil aircraft and therefore operations may be limited or prohibited. The various types of airspace may be designated as prohibited, restricted, warning, alert, military operations areas, and controlled firing areas. Hours of operation and effective altitudes may be listed directly on aeronautical charts or indexed by area number on a chart panel. The following are the types of special use airspace.

Prohibited areas contain airspace of defined dimensions identified by an area on the surface of the earth within which the flight of aircraft is prohibited. Such areas are established for security or other reasons associated with the national welfare. These areas are published in the Federal Register and are depicted on aeronautical charts.

Restricted areas include airspace where flight operations are subject to certain limitations. There may be unusual, often invisible, hazards to aircraft, such as artillery firing, aerial gunnery, or flight of guided missiles. Penetration of restricted areas without authorization from the controlling agency can be extremely hazardous. If ATC issues you an IFR clearance which will take you through restricted airspace, such a clearance constitutes authorization to penetrate the airspace. In this case, you need take no further action other than to comply with the clearance, as issued, and maintain normal vigilance.

A warning area is airspace of defined dimensions, extending from three nautical miles outward from the coast of the United States, that contains activity that may be hazardous to nonparticipating aircraft. The purpose of such warning areas is to warn nonparticipating pilots of the potential danger. A warning area may be located over domestic or international waters or both.

Alert areas are shown on sectional charts to inform you of areas that may contain a high volume of pilot training or an unusual type of aerial activity. Flight within alert areas is not restricted, but you are urged to exercise extreme caution. Pilots of participating aircraft, as well as pilots transiting the area, are equally responsible for collision avoidance.

Military operations areas, or MOAs, are established to separate certain military training from civilian flight operations. When you are flying IFR, you may be cleared through an active MOA if ATC can provide separation. Otherwise, ATC will reroute or restrict your flight operations. If you are flying VFR, you should exercise extreme caution within an active MOA. Information regarding route activity is available from any FSS within 100 nm of the area. Established MOAs are shown on sectional, VFR terminal area, and low altitude enroute charts. Before entering an active MOA under VFR, you should contact the controlling agency for traffic advisories.

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OTHER AIRSPACE AREAS

Other airspace areas include airport advisory areas, military training routes, and areas where temporary restrictions or limitations or prohibitions apply. Parachute jump areas are an example.

An airport advisory area encompasses the airspace within 10 sm of an airport where a nonautomated FSS is located and there is no operating control tower. At these locations, the FSS provides local airport advisory (LAA) service. When inbound with an operable radio, you should monitor the appropriate Common Traffic Advisory Frequency (CTAF) beginning approximately 10 miles from the airport. Recommended radio procedures are outlined in the Aeronautical Information Manual (AIM).

The centerlines of military training routes (MTRs) are depicted on sectional and NOS low altitude enroute charts. They involve both IFR and VFR high-speed operations. Generally, MTRs are established below 10,000 feet MSL for operations at speeds in excess of 250 knots. The IFR routes (IRs) may be operated in either IFR or VFR conditions, while VFR routes (FRs) are operated only under VFR conditions. You should contact an FSS within 100 nm of a particular MTR for current information on route usage.

Temporary flight restrictions are imposed by the FAA to protect persons and property on the surface or in the air. For example, the FAA will normally issue a Notice To Airmen (NOTAM) to provide a safe environment for rescue or relief operations and to prevent unsafe congestion above an incident or event which may generate high public interest. These situations include events such as forest fires, toxic spills, nuclear incidents, volcanic eruptions, and aircraft hijackings. The restricted airspace is usually limited to 2,000 feet above the surface within a two nautical mile radius. Incidents near controlled airports are handled through existing procedures and normally do not require issuance of a NOTAM. However, NOTAMs are issued to restrict flight in the vicinity of space flight operations and in the proximity of the President, Vice President, and other public figures. These flight limitations/prohibitions are put into place to reduce the hazards associated with aircraft operating in the vicinity of large assemblies of people. When such NOTAMs are issued, they are considered to be regulatory.

The Airport/Facility Directory contains a list of parachute jumping areas, with their times of operation and MSL altitudes. Frequently used sites are depicted on sectional charts.

Aircraft entering U.S. domestic airspace from points outside must provide identification prior to entry. Air Defense Identification Zones (ADIZs) have been established to facilitate this early identification. You must file a flight plan to penetrate or operate within a coastal or domestic ADIZ. Your flight plan must be filed with an appropriate facility, such as an FSS. If flying VFR, you file a defense VFR (DVFR) flight plan. It contains information similar to local flight plans, but helps to identify your aircraft as you enter the country. Unless otherwise authorized by ATC, a transponder with Mode C (or Mode S) capability is required, and the transponder must be turned on and operable. You are also required to have a two-way radio and periodically give ATC reports of your location while inbound toward the ADIZ. Failure to follow these steps may result in your aircraft being intercepted by U.S. security. The Alaskan ADIZ is similar to a contiguous U.S. ADIZ, except that it lies along the coastal waters of Alaska. In addition, the Alaskan ADIZ has different operating rules. If you are thinking of flying into the Alaskan ADIZ, you should refer to the Aeronautical Information Manual or the International Flight Information Manual for detailed procedural information.

During a defense emergency or during air defense emergency conditions, special security instructions may be issued in accordance with the Security Control of Air Traffic and Air Navigation Aids (SCATANA) Plan. Under the provisions of this plan, the military will direct the necessary actions to land, ground, divert, or disperse aircraft and take over control of navaids in the defense of the United States. IF SCATANA goes into effect, ATC facilities will broadcast instructions over available frequencies.

CLASS G AIRSPACE (UNCONTROLLED)

Class G airspace is that area which has not been designated as Class A, B, C, D, or E airspace and is essentially uncontrolled by ATC. Don't you just love government definitions. They don't tell you what it is, just what it is not! For example, the airspace below a Class E airspace area or below a Victor airway is normally uncontrolled. Most Class G airspace terminates at the base of Class E airspace at 700 or 1,200 feet AGL, or at 14,500 feet MSL. An exception to this rule occurs when 14,500 feet MSL is lower than 1,500 feet AGL. In this situation, Class G airspace continues up to 1,500 feet above the surface. The amount of uncontrolled airspace has steadily declined because of the expanding need to coordinate the movement of aircraft.

Although ATC does not have responsibility for or authority over aircraft in Class G airspace, most of the regulations affecting pilots and aircraft still apply. For example, although a flight plan is not required for IFR operations in Class G airspace, both pilot and aircraft must still be fully qualified for IFR flight. Day weather minimums for VFR flight in uncontrolled airspace are also reduced.

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