NATIONAL AIRSPACE SYSTEM

National Airspace System Lesson by wifiCFI


National Airspace System (PHAK C15)

The two categories of airspace are: regulatory and nonregulatory.

Within these two categories, there are four types: controlled, uncontrolled, special use, and other airspace. 

The categories and types of airspace are dictated by the complexity or density of aircraft movements, nature of the operations conducted within the airspace, the level of safety required, and national and public interest.

Class A Airspace

Dimensions

18,000’ MSL up to and including FL600.

Entry Requirements

All operations conducted under Instrument Flight Rules (IFR).

VFR Weather Minimums

N/A (IFR).

Class B Airspace

Dimensions

Customizable and surrounds big international airports.

Shaped like an upside down wedding cake.

Entry Requirements

ATC Clearance.

Minimum Private Pilot License or proper Student Pilot Endorsement.

Mode C Transponder.

VFR Weather Minimums

Visibility = 3 SM.

Cloud Clearance = Clear of clouds.

Class C Airspace

Dimensions

Customizable and surrounds congested airports.

Typically the upper shelf has a 10 NM radius and reaches up to 4,000’ AGL.

Typically the lower shelf has a 5 NM radius and reaches up to 1,200’ AGL.

Entry Requirements

Establish 2 way radio communications.

Mode C Transponder.

VFR Weather Minimums

Visibility = 3 SM.

Cloud Clearance = 1,000’ above, 500’ below, 2,000’ horizontal.

Class D Airspace

Dimensions

Customizable and surrounds small towered airports.

Typically reaches up to 2,500’ AGL with a radius of 4 NM.

Entry Requirements

Establish 2 way radio communications.

VFR Weather Minimums

Visibility = 3 SM.

Cloud Clearance = 1,000’ above, 500’ below, 2,000’ horizontal.

Class E Airspace

Dimensions

Can start of one of three floors and reaches up to the overlying airspace.

Start at: the surface, 700’ AGL, or 1,200’ AGL.

Entry Requirements

None for VFR.

VFR Weather Minimums

Below 10,000’ MSL:

Visibility = 3 SM.

Cloud Clearance = 1,000’ above, 500’ below, 2,000’ horizontal.

Above 10,000’ MSL:

Visibility = 5 SM.

Cloud Clearance = 1,000’ above, 1,000’ below, 1 SM horizontal.

Class G Airspace

Dimensions

Uncontrolled airspace that is not classified as A, B, C, D, or E.

From the surface to the overlying airspace.

Entry Requirements

None.

VFR Weather Minimums

Above 10,000’ MSL Day or Night:

Visibility = 5 SM.

Cloud Clearance = 1,000’ above, 1,000’ below, 1 SM horizontal.

1,200’ AGL to 10,000’ MSL during the Day:

Visibility = 1 SM.

Cloud Clearance = 1,000’ above, 500’ below, 2,000’ horizontal.

1,200’ AGL to 10,000’ MSL during the Night:

Visibility = 3 SM.

Cloud Clearance = 1,000’ above, 500’ below, 2,000’ horizontal.

Below 1,200’ AGL during the Day:

Visibility = 1 SM.

Cloud Clearance = Clear of clouds.

Below 1,200’ AGL during the Night:

Visibility = 3 SM.

Cloud Clearance = 1,000’ above, 500’ below, 2,000’ horizontal.

Special VFR Rules (FAR 91.157)

Special VFR operations may be conducted under the weather minimums and requirements of this section, instead of those contained in Sec. 91.155, 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.

The following rules must be followed:

Must have an ATC clearance (pilot requested, not ATC assigned)

Must remain clear of clouds

Flight visibility must be at least 1 SM

To takeoff, the ground visibility must be at least 1 SM

To perform Special VFR at Night:

Pilot and Plane must be Instrument Rated and Equipped.

Aircraft Speed Limits (FAR 91.117)

Below 10,000 MSL = 250 KIAS

Below 2,500 AGL and within 4 NM of a C or D airport = 200 KIAS

Below class B or through a class B VFR corridor = 200 KIAS

Special Use Airspace (PHAK C15)

Special use airspace or special area of operation (SAO) is the designation for airspace in which certain activities must be confined, or where limitations may be imposed on aircraft operations that are not part of those activities.

They include:

Prohibited Areas

Restricted Areas

Warning Areas

Military Operation Areas (MOAs)

Alert Areas

Controlled Firing Areas

Prohibited Areas

Prohibited areas contain airspace of defined dimensions 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.

The area is charted as a “P” followed by a number (P-40). 

Examples of prohibited areas include Camp David and the National Mall in Washington, D.C., where the White House and the Congressional buildings are located. 

Restricted Areas

Restricted areas are areas where operations are hazardous to nonparticipating aircraft and contain airspace within which the flight of aircraft, while not wholly prohibited, is subject to restrictions.

Restricted areas are charted with an “R” followed by a number (R-4401) and are depicted on the en route chart appropriate for use at the altitude or FL being flown. 

Information on Prohibited and Restricted Airspace is listed on the inside flap of the VFR Sectional.

Warning Areas

Warning areas are similar in nature to restricted areas; however, the United States government does not have sole jurisdiction over the airspace.

A warning area is airspace of defined dimensions, extending from 3 NM outward from the coast of the United States, containing activity that may be hazardous to nonparticipating aircraft. 

The purpose of such areas is to warn nonparticipating pilots of the potential danger. 

A warning area may be located over domestic or international waters or both. 

The airspace is designated with a “W” followed by a number (W-237).

Military Operation Areas (MOAs)

MOAs consist of airspace with defined vertical and lateral limits established for the purpose of separating certain military training activities from IFR traffic. 

Used to separate military and civilian operations.

Clearance is not needed under Visual Flight Rules.

Additional information on MOAs can be found on the inside flap of the VFR Sectional.

Alert Areas

Alert areas are depicted on aeronautical charts with an “A” followed by a number (A-211) to inform nonparticipating pilots of areas that may contain a high volume of pilot training or an unusual type of aerial activity. 

Pilots should exercise caution in alert areas.

Other Airspace Areas include:

Local Airport Advisory (LAA)

Military Training Routes (MTRs)

Temporary Flight Restrictions (TFRs)

Parachute Jump Aircraft Operations

Published VFR Routes

Terminal Radar Service Areas (TRSAs)

National Security Areas (NSAs)

Air Defense Identification Zones (ADIZ)

Wildlife/Wilderness Areas

Local Airport Advisory

An advisory service provided by Flight Service Station (FSS) facilities, which are located on the landing airport, using a discrete ground-to-air frequency or the tower frequency when the tower is closed. 

LAA services include local airport advisories, automated weather reporting with voice broadcasting, and a continuous Automated Surface Observing System (ASOS)/Automated Weather Observing Station (AWOS) data display, other continuous direct reading instruments, or manual observations available to the specialist. 

Military Training Routes (MTRs)

MTRs are routes used by military aircraft to maintain proficiency in tactical flying. 

These routes are usually established below 10,000 feet MSL for operations at speeds in excess of 250 knots. 

Some route segments may be defined at higher altitudes for purposes of route continuity. 

Temporary Flight Restrictions (TFRs)

A flight data center (FDC) Notice to Airmen (NOTAM) is issued to designate a TFR. 

The NOTAM begins with the phrase “FLIGHT RESTRICTIONS” followed by the location of the temporary restriction, effective time period, area defined in statute miles, and altitudes affected.

Examples of TFRs include:

Protection of public figures

Provide a safe area for disaster relief

Prevent unsafe congestion of sightseeing aircraft (Super Bowl)

Provide a safe area for space agency operations

Parachute Jump Operations

Parachute jump aircraft operations are published in the Chart Supplement U.S. (formerly Airport/Facility Directory). 

Sites that are used frequently are depicted on sectional charts.

Published VFR Routes

Published VFR routes are for transitioning around, under, or through some complex airspace. 

Terms such as VFR flyway, VFR corridor, Class B airspace VFR transition route, and terminal area VFR route have been applied to such routes. 

These routes are generally found on VFR terminal area planning charts (TAC).

Terminal Radar Service Areas (TRSAs)

TRSAs are areas where participating pilots can receive additional radar services. 

The purpose of the service is to provide separation between all IFR operations and participating VFR aircraft.

National Security Areas (NSAs)

NSAs consist of airspace of defined vertical and lateral dimensions established at locations where there is a requirement for increased security and safety of ground facilities.

Flights in these areas may be temporarily suspended for any number of reasons.

Air Defense Identification Zones (ADIZ)

All aircraft entering U.S. domestic airspace from points outside must provide for identification prior to entry or exit. 

ADIZs have been established to assist in early identification of aircraft in the vicinity of international U.S. airspace boundaries (AIM Section 6, 5-6-1).

For Defense VFR (DVFR) flights, the estimated time of ADIZ penetration must be filed with the appropriate aeronautical facility at least 15 minutes before penetration.

Wildlife/Wilderness Areas

FAA Advisory Circular AC 91−36, Visual Flight Rules (VFR) Flight Near Noise-Sensitive Areas, defines the surface of a national park area (including parks, forests, primitive areas, wilderness areas, recreational areas, national seashores, national monuments, national lakeshores, and national wildlife refuge and range areas) as: the highest terrain within 2,000 feet laterally of the route of flight, or the upper-most rim of a canyon or valley.

FAA Sources Used for this Lesson

Federal Aviation Regulations (FAR)

Aeronautical Information Manual (AIM)

Pilot’s Handbook of Aeronautical Knowledge (PHAK) Chapter 15

FAA Advisory Circular 91-36


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