Airspace and Air Traffic Control
Introduction
1. Whether at a small general aviation airport or at the largest of commercial airline hubs, every aircraft that operates into or out of an airport will either directly interact with, or at least be wary of, the complex hierarchy of organizations, facilities, and regulations that control the nation’s and the world’s airspace. In the United States, the Federal Aviation Administration owns and operates the facilities that make up the nation’s air traffic control system. In most of the rest of the world, the airspace above many nations is controlled by that nation’s local government, and supervised by the International Civil Aviation Organization (ICAO). In Pakistan, ATC is under Civil Aviation Authority of Pakistan. In recent years, few regions of the world have shifted to private or corporate ownership and operation of air traffic control. Examples include Air Services Australia, National Air Traffic Services, Ltd. (serving the United Kingdom), and NavCanada.
Brief History of Air Traffic Control
2. The roots of today’s air traffic control (ATC) systems began in the 1920s when pilots relied on scattered radio stations and rotating light beacons to fly from one airport to the next. First national ATC center originated at Newark Airport in Newark, New Jersey, in 1935. The duties of air traffic control at the time were to receive routine position reports from aircraft and monitor their respective courses along each of their planned routes. At the control center, each aircraft was physically identified by the creation of a “flight strip,” then known as “Shrimp Boats” and placed on a large map of the U.S. airspace. If two aircraft seemed like they were destined to converge, the control center would radio each pilot to warn aircraft of traffic in close range and perhaps make suggestions for slight course deviations to avoid a collision.
3. By 1950, the technology of air traffic control was significantly enhanced by the introduction of radar into the ATC environment. Radar had the capability of identifying aircraft locations as “blips” on radar scopes monitored by air traffic controllers. Subsequent advances in radar technology included transponder encoding technology which allowed air traffic controllers the ability to identify not only the location of the aircraft, but also its altitude, speed, and even the aircraft’s itinerary information, such as its originating airport and planned destination. With these technologies in place, and the aircraft in the skies flying at faster speeds, air traffic control adapted the concept of positive control for aircraft flying in higher altitudes, in poor visibility weather conditions, and around high traffic areas at low altitudes near the busiest airports. Under positive control, the air traffic controller determines the appropriate altitude, direction, and speed at which the aircraft should travel. If a pilot wishes to deviate from course, altitude, or speed, permission must be granted by air traffic control before any deviations may be made. By the mid-1970s, the FAA had achieved a semiautomatic air traffic control system based on a marriage of radar and computer technology. By automating certain routing tasks, the system allowed controllers to concentrate more effectively on the vital task of providing aircraft separation. In 1991, the FAA outlined a program for further enhancement of the air traffic control system, including higher levels of automation as well as new radar, communication, and weather forecasting systems.
Present Day ATC Management and Operating Infrastructure
4. In the United States, the air traffic control system is operated and managed in a hierarchical structure, ranging from control towers, which monitor and control the movement of aircraft at and around individual airports, to one system command center which oversees approximately 5,000 aircraft currently in flight, at any given point in time, over the entire United States.
Air Traffic Control System Command Center
5. At the top of the air traffic control operational hierarchy is the Air Traffic Control System Command Center (ATCSCC), was established in 1994 in Herndon, Virginia. The ATCSCC provides macro level management of every aircraft currently in the USA airspace system, as well as those aircraft with itineraries planned hours into the future. The role of the ATCSCC is to manage the flow of air traffic within the continental United States. The ATCSCC regulates air traffic when weather, equipment, runway closures, or other impacting conditions place stress on the National Airspace System. In these instances, traffic management specialists at the ATCSCC take action to modify traffic demands in order to reduce potential delays and unsafe situations in the air. Some of the strategies used by ATCSCC include the implementation of speed restrictions on aircraft, and imposition of ground delay programs, known as ground holds, on aircraft. Under a ground delay program, aircraft destined for an airport with potential delays upon arrival time will be held at its originating airport in order to avoid congestion and delays on route.
6. ATCSCC employs an Enhanced Traffic Management System (ETMS) to predict, on a national and local level, traffic surges, gaps, and volume based on current and anticipated airborne aircraft. ETMS specialists evaluated the projected flow of traffic into airports and airspace sectors and then implemented the least restrictive action necessary to ensure that traffic demand does not exceed system capacity. The ATCSCC is also responsible for issuing notices to airmen (NOTAMs) to provide the most up-to-date information regarding the status of the National Airspace System. Examples of NOTAM information include runway closures, malfunctions to navigational aids, missile and rocket launches, and any areas restricted because of national security issues.
Air Traffic Control
7. ATC is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able. In some countries, ATC may also play a security or defense role (as in the United States), or be run entirely by the military (as in Brazil). Preventing collisions is referred to as separation, which is a term used to prevent aircraft from coming too close to each other by use of lateral, vertical and longitudinal separation minima; many aircraft now have collision avoidance systems installed to act as a backup to ATC observation and instructions. In addition to its primary function, the ATC can provide additional services such as providing information to pilots, weather and navigation information and NOTAMs (Notices to Airmen).
8. In many countries, ATC services are provided throughout the majority of airspace, and its services are available to all users (private, military, and commercial). When controllers are responsible for separating some or all aircraft, such airspace is called "controlled airspace" in contrast to "uncontrolled airspace" where aircraft may fly without the use of the air traffic control system. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to follow, or merely flight information (in some countries known as advisories) to assist pilots operating in the airspace. In all cases, however, the pilot in command has final responsibility for the safety of the flight, and may deviate from ATC instructions in an emergency.
Pakistan Airspace Structure
9. In aviation a flight information region (FIR) is a region of airspace with specific dimensions, in which a flight information service and an alerting service are provided. It is the largest regular division of airspace in use in the world today. Smaller countries' airspace is encompassed by a single FIR, larger countries' airspace is subdivided into a number of regional FIRs. Pakistan Airspace is divided into 02 FIRs (Flight Information Regions) i.e. Karachi FIR & Lahore FIR.
10. Karachi FIR. Karachi FIR is consists of Enroute Air traffic Control and Terminal Air Traffic Control.
a. Enroute Air Traffic Control. ATC provides services to aircraft in flight between airports as well. Pilots fly under one of two sets of rules for separation visual flight rules (VFR) or Instrument flight rules (IFR). Air traffic controllers have different responsibilities to aircraft operating under the different sets of rules. While IFR flights are under positive control, in the US VFR pilots can request flight following, which provides traffic advisory services on a time permitting basis and may also provide assistance in avoiding areas of weather and flight restrictions. In ATC, an Area Control Center (ACC) is a facility responsible for controlling instrument flight rules aircraft en route in a particular volume of airspace (FIR) at high altitudes between airport approaches and departures. Karachi has three area control centres as KAR ACC East, KAR ACC West & KAR ACC North.
b. Terminal Air Traffic Control. Many airports have a radar control facility that is associated with the airport. In most countries, this is referred to as Terminal Control; in the U.S., it is referred to as a TRACON (Terminal Radar Approach Control.) While every airport varies, terminal controllers usually handle traffic in a 30-to-50-nautical-mile (56 to 93 km) radius from the airport. Terminal controllers are responsible for providing all ATC services within their airspace. Traffic flow is broadly divided into departures, arrivals, and over flights. As aircraft move in and out of the terminal airspace, they are handed off to the next appropriate control facility (a control tower, an en-route control facility, or a bordering terminal or approach control). Terminal control is responsible for ensuring that aircraft are at an appropriate altitude when they are handed off, and that aircraft arrive at a suitable rate for landing.
· Karachi Approach Control is within 50 NM area around Karachi
· Aerodrome control tower of respective locations
11. Lahore FIR. Lahore FIR also consists of Enroute Air traffic Control and Terminal Air Traffic Control.
a. Enroute Air Traffic Control. Lahore ACC (Area Control Centre) has 02 ACC Units i. e. LAH ACC East & LAH ACC West.
b. Terminal Air Traffic Control. Terminal air traffic control of Lahore FIS is as follows:-
i. Lahore Approach Control within 35 NM area around Lahore.
ii. Islamabad Radar Approach within 25 NM around Islamabad whereas some portion is controlled by CHERAT APPROACH jointly by PAF & CAA.
iii. Multan Tower/Approach within Terminal Control Area (Multan, Bahawalpur & D.G.Khan Airports falling therein).
iv. Aerodrome Control Tower of respective locations.
12. Basics of ATC. Aircraft flying between airports within the United States operate under varying levels of air traffic control, depending on the location and altitude at which they are traveling and the weather conditions while in flight. In many areas of the United States, particularly at low altitudes around unpopulated areas, aircraft may fly under no direct control by ATC. In contrast, in poor weather conditions, around busy air traffic areas, and at high altitudes, aircraft must fly under positive control, where altitude, direction, and speed of aircraft are dictated by air traffic controllers.
14. Traffic Pattern. All airports use a traffic pattern (traffic circuit) to assure smooth traffic flow between departing and arriving aircraft. Generally, this pattern is a circuit consisting of five "legs" that form a rectangle (two legs and the runway form one side, with the remaining legs forming three more sides). Each leg is named (see diagram), and ATC directs pilots on how to join and leave the circuit. Traffic patterns are flown at one specific altitude, usually 800 or 1,000 ft (244 or 305 m) above ground level (AGL). Standard traffic patterns are left-handed, meaning all turns are made to the left. Right-handed patterns do exist, usually because of obstacles such as a mountain, or to reduce noise for local residents. The predetermined circuit helps traffic flow smoothly because all pilots know what to expect, and helps reduce the chance of a mid-air collision.
7. At extremely large airports, a circuit is in place but not usually used. Rather, aircraft (usually only commercial with long routes) request approach clearance while they are still hours away from the airport, often before they even takeoff from their departure point. Large airports have a frequency called Clearance Delivery which is used by departing aircraft specifically for this purpose. This then allows airplanes to take the most direct approach path to the runway and land without worrying about interference from other aircraft. While this system keeps the airspace free and is simpler for pilots, it requires detailed knowledge of how aircraft are planning to use the airport ahead of time and is therefore only possible with large commercial airliners on pre-scheduled flights. The system has recently become so advanced that controllers can predict whether an aircraft will be delayed on landing before it even takes off; that aircraft can then be delayed on the ground, rather than wasting expensive fuel waiting in the air.
Visual Flight Rules (VFR) Versus Instrument Flight Rules (IFR)
12. One factor that determines the level of control an aircraft will depend on the type of flight rules the aircraft is operating under. The flight rules depend on the weather conditions during flight. Under weather conditions where the visibility is sufficient to see and avoid other aircraft, and the pilot can keep the aircraft sufficiently clear of clouds, the pilot may operate under visual flight rules (VFR). When visibility is insufficient or a pilot’s route takes the aircraft through clouds, the aircraft must fly under instrument flight rules (IFR). While flying under VFR, there are often times when positive control by ATC is unnecessary; under IFR, positive control is mandated.
Airspace Classes
13. The visibility and cloud clearance criteria determining whether or not an aircraft must fly under IFR versus VFR depends largely on the class of airspace through which the aircraft will be flying. The airspace class of any given location in the United States is defined by the FAA and identified by pilots by referencing air traffic control maps, called sectionals, terminal area charts, or aeronautical charts. It is important for airport management, as well, to identify the class of airspace under which their airport lies, for it certainly has an impact on aircraft operations at the airport. Since 1993, airspace has been classified as Class A, Class B, Class C, Class D, Class E, or Class G airspace.
a. Class A. Class A airspace, known as Positive Control Airspace, is located continuously throughout the continental United States, including the waters surrounding the continental United States out to 12 miles from the coastline, and Alaska, beginning at an altitude of 18,000 feet above sea level (MSL) up to 60,000 feet MSL (known as FL 600). Unless otherwise authorized, all aircraft operating in Class A airspace must operate under IFR. Class A airspace is controlled by ATC at Air Route Traffic Control Centers (ARTCCs). There are 21 ARTCCs in the United States, each controlling one of 20 adjacent areas in the continental United States, and the area surrounding Alaska.
b. Class B Airspace. Class B airspace, known as Terminal Radar Service Areas (TSRA) surrounds the nation’s busiest airports. The configuration of each Class B airspace area is specific to each area, but typically consists of a surface area and two or more layers of controlled airspace. The shape of Class B airspace is often described as an “upside down wedding cake.” Generally, Class B airspace centers around the busiest airport in the area, extending from the surface to 10,000 ft MSL. Aircraft flying under VFR must be able to remain clear of clouds while in Class B airspace. All aircraft flying in Class B airspace fly under the control of ATC. Class B airspace is identified by thick dark blue lines, and altitude designations on aeronautical charts.
c. Class C Airspace. Class C airspace, known as Airport Radar Service Areas (ARSA), surrounds those airports that serve moderately high levels of IFR operations or passenger enplanements. Class C is generally considered areas of moderate air traffic volumes, but not as busy as Class B airspace. Class C airspace is usually centered around an airport of moderately high volumes of traffic, ranging from the surface to 4,000 feet above the airport’s elevation within 5 miles of the airport, and from 1,200 ft above the surface to 4,000 ft above the surface from 5 to 10 miles from the airport. Class C airspace is also in the form of an inverted wedding cake. When in Class C airspace, each aircraft must establish two-way radio communications with the ATC facility providing air traffic services prior to entering the airspace, and thereafter maintain those communications while in the airspace. To fly under VFR, there must exist at least 3 miles of visibility and aircraft must be able to remain at least 500 ft below, 1,000 ft above, and 2,000 ft horizontally from any clouds. ATC will control aircraft flying under both VFR and IFR to maintain adequate separation from other aircraft under IFR. Aircraft flying VFR are responsible to see and avoid any other traffic. Class C airspace is identified by solid magenta rings and altitude designators on aeronautical charts.
d. TRACONs. Class B and Class C airspace, as well as some airspace extending beyond the limits of Class B and Class C airspace, is typically serviced by a Terminal Radar Approach Control (TRACON) facility. There are 185 TRACON facilities located within the United States controlling air traffic within approximately a 30-mile radius of the busiest airport in the area, from altitudes under 15,000 feet MSL, with the exception of the areas immediately surrounding the airport, which are typically controlled by an air traffic control tower (ATCT). The primary objectives of TRACON controllers are to facilitate the transition of aircraft to and from the local airport’s airspace into an aircraft’s en route phase of flight, and to coordinate the typically high volumes of air traffic flying within the area. TRACON facilities operate strictly by monitoring aircraft by radar and hence may not necessarily be located on airport property, although many are.
e. Class D Airspace. Class D airspace, known as Airport Traffic Areas or Control Zones (CZ), surrounds those airports not in Class B or Class C airspace but do have an air traffic control tower in operation. Class D airspace is generally a cylindrical area, 5 miles in radius from the airport, ranging from the surface to 2,500 above the elevation of the airport. Unless authorized, each aircraft must establish two-way radio communications with the ATC facility providing air traffic services prior to entering the airspace and thereafter maintain those communications while in the airspace. While IFR traffic is controlled by ATC to maintain adequate separation in the airspace, VFR traffic generally is not, except when performing runway operations (takeoffs or landings). In order to operate VFR in Class D airspace, pilots must have at least 3 miles of visibility and be able to remain at least 500 feet below, 1,000 feet above, and 2,000 feet horizontally from clouds. Class D airspace is identified by a dashed blue ring and altitude designator on aeronautical charts.
f. Class E airspace, known as General Controlled Airspace, generally exists in the absence of Class A, B, C, or D airspace extending upward from the surface to 18,000 feet MSL within 5 miles of airports without control towers. In other areas, Class E airspace generally exists from 14,500 feet MSL to 18,000 feet MSL over the contiguous United States, including the waters within 12 miles off the coast, and Alaska. In addition, federal airways, known as Victor Airways, and Jet Routes, which generally exist from 700 or 1,200 ft above the ground (AGL) are considered Class E airspace. Only aircraft operating under IFR receive positive control in Class E airspace. VFR traffic is responsible to see and avoid all traffic. All aircraft operating under VFR must have at least 3 miles of visibility and be able to remain at least 500 ft below, 1,000 ft above, and 2,000 ft horizontally from clouds at altitudes below 10,000 ft and must have at least 5 miles of visibility and remain 1,000 ft above, 1,000 ft below, and 1 mile clear of clouds at or above 10,000 ft MSL.
g. Class G airspace, known as Uncontrolled Airspace, encompasses the airspace in the absence of Class A, B, C, D, or E airspace. This limited area typically reaches from the surface to 14,500 feet MSL in areas that aren’t part of federal airways, and from the surface to 700 or 1,200 feet AGL in areas that are part of federal airways. Many remote airfields lie under Class G airspace, and hence have the very basic minimum of air traffic control services, if any at all. Aircraft flying in Class G airspace receive air traffic control assistance only if the workload on air traffic controllers permits. Aircraft flying under IFR generally do not operate in Class G airspace.
h. Victor Airways and Jet Ways. Whether flying by VFR or IFR rules, aircraft flying within the airspace system have traditionally been encouraged to fly on designated corridors known as Federal Air Routes. At low altitudes, the air routes are known as Victor Airways, named so because they are typically defined by a direct line from one VOR navigation facility to another. Victor Airways are typically 8 nautical miles in width and generally range from 1,200 above the ground (AGL) up to but not including 18,000 feet above sea level (MSL). Victor Airways are identified by light blue lines and designators [denoted by a V followed by a route number (e.g., V123)] on low-altitude aeronautical charts. At altitudes between 18,000 feet MSL and 45,000 feet MSL, routes are known as Jet Routes. Jet Routes are identified as magenta lines and designators [denoted by a J followed by a route number (e.g., J4)] on high-altitude aeronautical charts.
14. Classes A–E are referred to as controlled airspace. Classes F and G are uncontrolled airspace. The table below provides an overview of the above classes, and the specifications for each.
| Class | ATC Clearance | Separation | Traffic Information | ||||
| A | Controlled | Yes | Yes | No | Required | Provided for all flights | N/A |
| B | Controlled | Yes | Yes | Yes | Required | Provided for all flights | N/A |
| C | Controlled | Yes | Yes | Yes | Required | Provided for all IFR/SVFR | Provided for all VFR |
| D | Controlled | Yes | Yes | Yes | Required | Provided for IFR/SVFR to other IFR/SVFR | Provided for all IFR and VFR |
| E | Controlled | Yes | Yes | Yes | Required for IFR | Provided for IFR/SVFR to other IFR/SVFR | Provided for all IFR to VFR where possible |
| F | Uncontrolled | Yes | No | Yes | Not Required | Provided for IFR/SVFR to other IFR/SVFR where possible | Provided where possible |
| G | Uncontrolled | Yes | No | Yes | Not Required | Not provided | Provided where possible |
Special-Use Airspace
15. ATC designates certain areas of airspace as special-use airspace (SUA), designed to segregate flight activity related to military and national security needs from other airspace users. There are six different kinds of special-use airspace: prohibited areas, restricted areas, military operations areas, alert areas, warning areas, and controlled firing areas.
a. Prohibited Areas are established over security-sensitive ground facilities such as the White House, certain military installations, and presidential homes and retreats. All aircraft are prohibited from flight operations within a prohibited area unless specific prior approval is obtained from the FAA or the local controlling agency.
b. Restricted Areas are established in areas where ongoing or intermittent activities occur that create unusual hazards to aircraft, such as artillery firing, aerial firing, and missile testing. Restricted areas differ from prohibited areas in that most restricted areas have specific hours of operation. Entry during restricted hours requires specific permission from the FAA or the local controlling agency.
c. Military Operations Areas (MOA) are established to contain certain military activities, such as air combat maneuvers, intercepts, and acrobatics. Civilian flights are allowed within an MOA even when the area is in use by the military. ATC will provide separation services for IFR traffic within MOAs.
d. Alert Areas contain a high volume of pilot training or an unusual type of aerial activity, such as helicopter activity near oil rigs, which could present a hazard to other aircraft. There are no special requirements for operations within alert areas other than heightened vigilance by pilots.
e. Warning Areas contain the same kind of hazardous flight activity as restricted areas, but are located over domestic and international waters. Warning areas generally begin 3 miles offshore.
f. Controlled Firings Areas contain civilian and military activities that could be hazardous to nonparticipating aircraft, such as rocket testing, ordnance disposal, and blasting. They are different from prohibited and restricted areas in that radar or a ground lookout is used to indicate when an aircraft is approaching the area, at which time all activities are suspended.
Flight Service Stations (FSS)
16. A Flight Service Station (FSS) is an air traffic facility that provides information and services to aircraft pilots before, during, and after flights, but unlike air traffic control (ATC), is not responsible for giving instructions or clearances or providing separation. The people who communicate with pilots from an FSS are referred to as specialists rather than controllers, although in the US, FSS specialists' official job title is air traffic control specialist - station. The precise services offered by stations vary by country, but typical FSS services may include providing preflight briefings including weather and notices to airmen (NOTAMs); filing, opening, and closing flight plans; monitoring navigational aids (NAVAIDs); collecting and disseminating pilot reports(PIREPs); offering traffic advisories to aircraft on the ground or in flight; relaying instructions or clearances from air traffic control; and providing assistance in an emergency. In many countries, flight service stations also operate at mandatory frequency airports to help co-ordinate traffic in the absence of air traffic controllers, and may take over a control tower frequency at a controlled airport when the tower is closed.
Current and Future Enhancements to Air Traffic Control
17. The capacity of today’s national airspace system is constrained by rules, procedures, and technologies that require air traffic controllers to direct aircraft within narrow, often inefficient guidelines. As air traffic continues to grow, these inefficiencies and their associated costs are compounded. Responding to these limitations, the FAA and the aviation industry are working together on two major, interdependent capacity initiatives: free flight and NAS modernization.
18. Free Flight. Free flight is a concept for safe and efficient flight operating capability under IFR in which pilots have the freedom to select their own path and speed in real time. Air traffic restrictions are imposed only to ensure separation, to preclude exceeding airport capacity, to prevent unauthorized flight through special-use airspace, and to ensure the safety to flight. Restrictions are limited in extent and duration to correct the identified problem. Any activity that removes restrictions represents a move toward free flight. The transition to free flight requires changes in air traffic philosophies, procedures, and technologies. The principal philosophical change required for free flight is a shift from the concept of air traffic control (ATC) to air traffic management (ATM). ATM differs from ATC in several ways: the increased extent of collaboration between users and air traffic managers, greater flexibility for users to make decisions to meet their unique operational goals, and the replacement of broad restrictions with user-determined limits and targeted restrictions only when required.
19. Under the current air traffic system, aircraft are frequently restricted to ATC-preferred routes, which may not be the routes preferred by the pilot or air carrier. Air traffic controllers direct pilots to changes their direction, speed, or altitude to avoid adverse weather or traffic congestion. In contrast, free flight will grant pilots substantial discretion in determining their routes. This is possible because enhanced technologies will provide accurate weather and traffic information directly to the cockpit. Many decisions will be collaborative, taking advantage of the best information available to the pilot and air traffic manager to ensure safe and efficient flight.
20. NAS Modernization. To achieve the free flight concept and accommodate projected increases in air traffic, the FAA is modernizing and replacing much of the equipment, computers, and software used to manage air traffic and assure safe operations. Modernization of the NAS is intended to give users new abilities such as flexible departure and arrival routes and increased usage of preferred flight trajectories. The goal of NAS modernization is to increase the flexibility and efficiency of the NAS by improving traffic flow and weather predictability, and reduce user operating costs. The challenge to NAS modernization lies within maintaining a balance between the need to sustain and replace current critical ATC infrastructure with the desire to provide new capability to NAS users. The principal NAS modernization changes may be categorized into five functional areas: communications, navigation, surveillance, weather, and air traffic management.
a. Communications. NAS modernization intends to reduce the required amount of voice-to-voice communication between aircraft and ground facilities with the implementation of electronic data transfer between the flight deck and air traffic management systems using digital data link technology.
b. Navigation. In recent years, navigation has become increasingly reliant on the satellite based Global Positioning System (GPS). Contrary to the traditional ground based navigation systems such as NDBs, VORs, and ILSs, GPS is a space-based radio positioning, navigation, and time-transfer system. In July 1995, GPS gained full operational capability for civilian use, although with reduced accuracy.
d. Surveillance. Knowing the position and intended path of aircraft relative to other aircraft, both on the ground and in the air, is necessary to ensure safe separation. The accuracy and certainty with which aircraft positions can be tracked determines the procedures and spacing allowed to maintain safe operations. Enhanced surveillance improves the efficiency of airspace usage by allowing reduced separation requirements, for example. In order to realize reduced separations standards, the free flight concept imposes particularly high demands on the ability to accurately and reliably locate and track the movement of aircraft with greater precision and at a faster update rate than is used today.
e. Weather. Today’s fragmented weather gathering, analysis, and distribution systems are being enhanced by a more harmonized, integrated system. Incremental improvements in weather detection sensors, processors, dissemination systems, and displays are also occurring.
f. Air Traffic Management. Managing air traffic and airspace utilization is becoming increasingly augmented with computer-based decision support systems. These systems are intended to improve the efficiency and effectiveness of NAS-wide information, enhancing all phases of surface and flight operations.
Operational Enhancements to ATC
21. A cost-efficient alternative to airport and airspace development is the modification and enhancement of current air traffic control operating procedures to improve the flow of aircraft within the NAS. Examples of initiatives in the enroute air traffic environment are the National Route Program (NRP) and the 3D User-Preferred Trajectories Flight Trials Project, both of which are intended to decrease restrictions on aircraft and allow pilots to fly more direct routes. In the oceanic environment, reduced horizontal and vertical separation standards are intended to provide more airspace availability and to provide pilots with more flexibility and efficient routing. Additionally, less-restrictive instrument approach procedures are being developed for the terminal environment as the accuracy of NAVAIDs used for approaches improves.
Reduced Vertical Separation Minima (RVSM)
22. The goal of RVSM (Reduced Vertical Separation Minima) is to reduce the vertical separation above flight level (FL) 290 from the current 2,000-foot minimum to a 1,000-foot minimum. This will allow aircraft to safely fly more optimum routes, gain fuel savings, and increase airspace capacity. The process of safely changing this separation standard requires a study to assess the actual performance of airspace users under the current separation (2,000 feet) and potential performance under the new standard (1,000 feet). In 1988, the ICAO Review of General Concept of Separation Panel (RGCSP) completed this study and concluded that safe implementation of the 1,000-foot separation standard was technically feasible. The proposal to implement RVSM between FL 290–410 (inclusive) January 20, 2005 is considered to be a feasible option and the FAA is developing its plans accordingly. The goal of DRVSM is to achieve in domestic airspace those user and provider benefits inherent to operations conducted at more-optimum flight profiles and with increased airspace capacity. Full DRVSM will add six additional usable altitudes above flight level (FL) 290 to those available under today’s Conventional Vertical Separation Minimum system. The ATC system will experience increased benefits, which have already been achieved in those oceanic areas wherein RVSM has become operational.
30. Reduced Horizontal Separation Minima (RHSM). In April 1998, oceanic lateral separation standards were reduced from 100 nautical miles (nm) to 50 nautical miles in the Anchorage airspace of the North Pacific. Longitudinal separation minima were also reduced in the North Pacific from the time-based standard of 15 minutes to 50 nautical miles. The FAA expanded the 50-nauticalmiles lateral and longitudinal separation standards to the Central Pacific airspace for all qualified aircraft in December 1998. By 2002, RHSM had been implemented on Central East Pacific Routes, as well. The timetable for RHSM includes 50-nautical-miles separation minima on all oceanic routes by 2004, and reduced lateral separation minima to 30 nautical miles by 2005.
Terminal Area Enhancements
31. A number of visual and electronic landing aids at or near airports assist pilots in locating the runway, particularly during IMC. Approach procedures have traditionally been based on the type and accuracy of landing aids available, geography, traffic, and other factors. As navigational technologies improve, operating procedures for approach are modified and enhanced commensurate with the characteristics of the new technology. Some of these enhancements are discussed below.
a. Removal of the 250-knot speed limit for departing A/C in Class B airspace under 10,000 ft MSL. Aircraft are currently restricted to speeds at or below 250 knots below 10,000 feet MSL. This restriction can constrain capacity by limiting departure rates from busy terminal areas. In June 1997, the FAA began field-testing the removal of the 250-knot speed restriction for departures from the Houston, Texas, Class B airspace. In the field test, controllers were given the authority to remove the speed restriction. American Airlines reviewed a month of efficiency data for over 400 Houston departures that participated in the field trial. They found significant savings of approximately half a minute and 100 pounds of fuel per flight.
b. Simultaneous Converging Instrument Approaches (SCIA) Under existing approaching procedures, converging runways can be used for independent streams of arriving aircraft only when the cloud ceiling is at least 1,000 feet and visibility is at least 3 statute miles. This requirement decreases runway capacity in IMC and causes weather-related delays. Simultaneous approaches may not normally be conducted under IMC if the converging runways intersect. However, a new missed-approach procedure, requiring a 95-degree turn and a flight management system in the cockpit, may enable use of SCIA with ceilings as low as 650 feet. Following validation and further flight-testing, these minima could be reduced to as little as 500 feet.
Concluding Remarks
32. The FAA’s complex system of management hierarchies, facilities, policies, and technologies that make up air traffic control plays a vital role in the management of the civil aviation system in general and the operation of airports in particular. Although ultimate strategic and daily operational decisions on the control of air traffic lie with government or contracted air traffic controllers, as well as pilots of commercial and general aviation aircraft, knowledge of the air traffic control system, with particular respect to local airspace classifications, the presence of particular navigational aids, and policies for aircraft operations on and within the vicinity of the airport, is vital to the overall efficient management of the airport.
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