Aircraft Situational Display

Most commercial and many general aviation aircraft fly under Instrument Flight Rules (IFR).  In contrast to Visual Flight Rules (VFR) in which pilots keep their distance from other aircraft under "see and be seen" principles, aircraft under IFR are positioned  by air traffic controllers.  Radar is used to keep track of the location of the aircraft.  The major purpose of air traffic control is to separate aircraft to avoid collisions.

There are two types of air traffic control.  Terminal air traffic control operates in the airspace surrounding the airport, usually at a 40-mile radius between 6,000 to 12,000 feet.  Enroute air traffic control is used for the remaining airspace between 700 to 60,000 feet within the continental United States. 

Twenty Air Route Traffic Control Centers (ARTCC) across the country control the airspace.  Each ARTCC communicates with the Terminal air traffic facilities within its boundaries and neighboring Air Route Traffic Control Centers.  The following map displays the ARTCC zones across the continental United States.

(insert ARTCC government map)

An ARTCC airspace is split up into smaller, manageable pieces of airspace called "sectors". Sectors have vertical as well as horizontal boundaries.  A few sectors extend from the ground up, but most are stratified, with the lowest sectors defined from the ground to 23,000 feet, with another sector above from 24,000 feet and up.  In some cases, a third sector may be defined for 37,000 feet and up.  One or two controllers are directly responsible for separating the aircraft within their sector.  Each sector has a unique radio frequency which the controller uses to communicate with the pilots.  As aircraft transition from one sector to another, they are instructed to change the frequency to the next sector.

Data is passed from one ARTCC sector to the next as a plane flies across the country.  These data messages, called Flight Movement Messages, are the same messages are used for Aircraft Situational Display Information (ASDI).  ASDI has been available to the airline industry since 1991.  The National Business Aviation Association (NBAA), the General Aviation Manufacturers Association, the Aircraft Owners & Pilots Association, the Helicopter Association International and the National Air Transportation Association petitioned the FAA to make ASDI information available on a "need-to-know" basis in 1995.  Subsequently, NBAA advocated the broad-scale dissemination of ASDI data.  In 1997, NBAA began working with the FAA and ASDI vendors to develop a Vendor Code of Conduct that would help protect the privacy of general aviation operators that fly under IFR.  All ASDI Vendors signed the voluntary Code of Conduct in September 1998 that would block ASDI data at the request of the operator.

Aircraft Situation Display to Industry (ASDI) data are now available to private subscribers through several vendors.  The ASDI information includes the location, altitude, airspeed, destination, estimated time of arrival and tail number or designated identifier of air carrier and general aviation aircraft operating on IFR flight plans within U.S. airspace.  Subscribers to this service include flight departments, charter operators, limousine firms, aircraft producers, air carriers, and research firms.

A detailed report on the ASDI system is available in this PDF document - Aircraft Situational Display to Industry:  Functional Description and Interface Control Document.

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