Airspace

Airspace exists to protect something, whether that be certain aircraft at busy airports, or military operations areas.  There are two primary types of airspace - Controlled and Uncontrolled

Types of Controlled Airspace

Class A
Class B
Class C
Class D
Class E

Class A Airspace is primarily for high-altitude enroute traffic.  It exists at and above 18,000 ft MSL up to FL 600.  Requires instrument-rated aircraft with instrument-rated pilots on instrument flight plan.  Requires Mode C Transponder.

Class B exists around the busiest international airports like O'Hare, LAX, Atlanta, or JFK.  Its dimensions vary depending on surrounding airports or terrain features.  Its area is generally from the surface to 10,000 ft MSL.  An ATC clearance is required, as well as Mode C Transponder.

Class C exists around busy airports that aren't busy enough to justify a Class B designation.  They consist of an inner area and a shelf area.  Their dimensions may vary, but are typically surface to 4000 ft AGL inner area with an outer shelf area extending 10nm from 1200 to 4000 ft AGL.  Mode C transponder is required as well as two-way radio communications.

Class D exists around towered airports that are not busy enough commercially to justify a Class C rating.  Area is generally surface to 2500 ft AGL.  Two-way radio communications required.

Class E exists in all areas not covered by the above airspace.  It extends upward from the surface, from 700 ft. AGL or 1200 ft. AGL.  If it is not designated on a chart, it begins at 14,500 ft MSL. and continues up to 18,000 ft MSL.  It begins again above FL 600.

Uncontrolled Airspace

Class G Airspace is airspace that ATC has no authority or responsibility to control traffic.  Pilots are on their own for traffic separation and adherence to weather mins etc.  Its dimensions begin at surface and go up to base of overlying airspace (usually Class E).

Special Use Airspace

Protects an area where it is safer to confine an activity.  Certain limitations may exist for entering traffic or there may be no limitations at all.  From least restrictive to most restrictive they are, . . .

Controlled Firing Areas - These are not depicted on charts because they discontinue activities immediately if an aircraft is spotted in the vicinity.

Alert Areas - Shown on charts and begin with "A-   "  Contain a high volume of training aircraft or other aerial activity.  No special entry requirements, but extra vigilance in traffic avoidance should be maintained.

Military Operations Areas - have defined lateral and vertical limits to separate military training from IFR traffic.  If in use, nonparticipating IFR traffic may be cleared through or vectored around the area.  Aircraft participating are not subject to speed limits and may be flying at low level.

Restricted Areas - Similar to MOAs, but more hazardous because now there may be live ordnance.  IFR flights may still be authorized.  If Restricted area is not active, ATC may route traffic through it.  If it is active or not handed over to the FAA, ATC will vector traffic around.

Warning Areas - Essentially the same as a Restricted area, but extends 12NM outward from the coast.   May be over U.S. or international waters or both.  There aren't entry restrictions as in a restricted area, but extreme caution should be exercised - particularly when offshore, a pilot may inadvertently enter international airspace and face difficulty reentering.

Prohibited Areas - Entry is prohibited!  This would include areas around Cape Canaveral, White House and the National Mall or other areas where national security is absolutely necessary.

Other Airspace Areas

Local Airport Advisory (LAA) - Facilities provided at landing airport with communications and ASOS/AWOS.  FSS acts as tower in a way.  Recommended but not required.

Military Training Routes - Used by military.  No speed limit.  Begin with either IR (Instrument) or VR (Visual).  3 digits indicates above 1500 ft. AGL  4 digits indicates below 1500ft. AGL.

Temporary Flight Restrictions - FDC Notam issued.  Can exist around President's arrival on Air Force One.  Dimensions are 30nm for presidential TFR typically.  They may also exist to provide safe operating area for disaster relief operations, or to protect a sporting event.  Which games generate TFRs is not in any officially published document.  Use google and be familiar with the area in which you are flying.

Parachute Jump Aircraft Operations - are depicted on charts and published in the A/FD

Published VFR Routes - exist to transition or work around complex airspace.  An example would be Special Flight Rules through LAX.

TRSAs - Functions as controlled airspace similar to Class D around primary airport.  Participation is voluntary, but recommended.

National Security Areas - Pilots requested to avoid flying through these depicted areas.

Weather Requirements

The weather requirements are based upon the level of control that the controlling facility/airspace has.  Ultimately, it depends on how much time or visibility is needed to avoid other traffic.