Top

Class Alpha Airspace

Introduction:

  • Class Alpha airspace is positive control airspace, meaning Air Traffic Control (ATC) can positively see and track aircraft, considered for "cruise" altitudes and is the beginning of "Flight Levels" in the United States
  • Within these "cruise" altitudes there are different types of airways which are structured much the same as Low Altitude Victor Routes:
  • Reduced Vertical Separation Minimum (RVSM) begins at FL290 and extends up through, to include, FL410
  • All altitudes are assigned as pressure altitude (synonymous with Flight Level) which means your altimeter shall be set to the standard of 29.92 inHg
    • The use of the standard 29.92 has a number of implications you must understand
  • Class Alpha airspace is not charted, see dimensions below
Airspace Dimensions
Figure 1: General Airspace Overview

Airspace Dimensions:

  • Vertically, Class Alpha begins at 18,000' MSL up to and including FL600 (about 60,000')
  • Horizontally, Class Alpha begins when within 12 NM of coast in 48 contiguous states and Alaska; and designated international airspace beyond 12 nautical miles off the coast of the 48 contiguous States and Alaska within areas of domestic radio navigational signal or ATC radar coverage, and within which domestic procedures are applied
    • Examples include Santa Barbara Island, Farallon Island and airspace south of latitude 25°04;00" North
  • Does not include the airspace less than 1,500 feet above the surface of the earth and the Alaska Peninsula west of longitude 160°00'00" West

Airspace Depiction:

  • Class A airspace is not depicted on any chart

ATC Facility:

Jet Routes:

  • Within the cruise altitudes there are Jet Routes, or "J" Routes, which are highways in the sky, much the same as Victor routes
  • Jet Routes begin at 18,000' MSL and end at Flight Level (FL) 450 (about 45,000')
  • The letter "J" precedes a number to label the airway
  • Note the range of Jet Routes is actually less than the dimensions of Class Alpha airspace [Figure 2]
    • Limited due to Standard Service Volume (SSV) of ground stations
  • Jet routes have no defined width
  • A NAVAID on a continuing jet route is NOT part of the segment and not to be included on your flight plan

Q Routes:

  • Q Routes are available for use by RNAV equipped aircraft between 18,000' MSL and FL450 (about 45,000') inclusive, same as J Routes
  • Q Routes are depicted on En-route High Altitude Charts [Figure 2]
    • Operation above FL450 (about 45,000') may be conducted on a point-to-point basis
  • Area navigation (RNAV) routes have been established in both the low-altitude and the high-altitude structures in recent years and are depicted on the en route low and high chart series
  • High altitude RNAV routes are identified with a "Q" prefix (except the Q-routes in the Gulf of Mexico) and low altitude RNAV routes are identified with a "T" prefix
  • RNAV routes and data are depicted in aeronautical blue
  • In addition to the published routes, a random RNAV route may be flown under IFR if it is approved by ATC
  • Random RNAV routes are direct routes, based on RNAV capability, between waypoints defined in terms of latitude/longitude coordinates, degree-distance fixes, or offsets from established routes/airways at a specified distance and direction
  • Radar monitoring by ATC is required on all random RNAV routes
  • These routes can only be approved in a radar environment
  • Factors that are considered by ATC in approving random RNAV routes include the capability to provide radar monitoring and compatibility with traffic volume and flow
  • ATC will radar monitor each flight; however, navigation on the random RNAV route is the responsibility of the pilot
Jet Routes and Q Routes
Figure 2: High Altitude En-route Chart

Operations:

VFR Visibility Requirements:

  • Each person operating an aircraft in Class A airspace must conduct operations under Instrument Flight Rules (IFR), unless otherwise authorized
    • See 14 CFR Section 71.33 and 14 CFR Section 91.167 through 14 CFR Section 91.193

Entry Requirements:

Communications:

  • Unless otherwise authorized by ATC, each aircraft operating in Class A airspace must be equipped with a two-way radio capable of communicating with ATC on a frequency assigned by ATC
  • Each pilot must maintain two-way radio communications with ATC while operating in Class A airspace

Qualifications:

  • Instrument rating

Aircraft Separation:

  • Separation is provided for all aircraft
  • It is critical that pilots change their altimeter setting from the local altimeter to 29.92 when climbing through 18,000 feet
    • This ensures all aircraft flying in class A airspace have the same altimeter setting and will have proper altitude separation
  • Non-RVSM separation is 2,000' vertically
  • RVSM separation is 1,000' vertically

Restrictions:

  • As assigned

Deviations:

  • An operator may deviate from any provision of this section under the provisions of an ATC authorization issued by the ATC facility having jurisdiction of the airspace concerned
  • In the case of an inoperative transponder, ATC may immediately approve an operation within a Class A airspace area allowing flight to continue, if desired, to the airport of ultimate destination, including any intermediate stops, or to proceed to a place where suitable repairs can be made, or both
  • Requests for deviation from any provision of Federal Aviation Regulation 91.215 must be submitted in writing, at least 4 days before the proposed operation
    • ATC may authorize a deviation on a continuing basis or for an individual flight

Conclusion:

  • Class Alpha airspace is the only classification of airspace that is not depicted on a sectional chart
  • There is no Class A airspace over Hawaii and the Victor airways have no upper limit in Hawaii

References: