ATC+Operations

=AIR TRAFFIC CONTROL=

toc Air Traffic Control (ATC) is a service provided to aircraft pilots in controlled airspace by a network of ground-based controllers. Controllers are responsible for smoothly expediting aircraft to and from airports as safely and efficiently as possible all over the world. Controllers take on many roles in order to carry out their responsibility. Some of these roles include: ensuring a safe runway for an aircraft to takeoff and land, alerting pilots to other traffic in their area (position, speed, altitude, and direction of travel reports), directions to destinations, aiding pilots in avoiding adverse weather, ensuring safe distances between aircraft, assisting the pilot and clearing the surrounding areas during an aircraft emergency, and much more.

HISTORY
Before 1926, there was little need for ground-based control of aircraft. The United States developed a set of air traffic rules for navigation, protection, aircraft identification, prevention of collisions between aircraft and vessels and safe altitudes of flight. All of these rules and regulations made the Air Commerce Act of 1926. The Air Commerce Act still didnt help the prevention of collisions; therefore an Air Traffic Control of visual signals began. The first flagman of this type of system was Archie League in the early 1920's in St. Louis, Missouri. In 1930, Cleveland Municipal Airport was the first to use a radio equipped air tower. Then shortly after that, all airline aircraft were being retrofitted with radio-telephone communication. Airway Traffic Control Centers were set up in Newark, NJ, Chicago, and Cleveland in 1936 to help guide traffic as more people began to use the sky as a form of travel. ATC became a federal responsibility in July of 1936. In 1941, the Civil Aeronautics Administration ( which later became the FAA) constructed and operated ATC towers which climbed to 115 in 1944. As a result of WWII, technology that was being used during the war transferred over to the civilian side after the end of the war. ATC began using radar for approach and departure control in the major traveled airports. In 1960, the FAA considered a designated area around airports as positive control area and aircraft were required to carry transponders. This allowed the ATC to see the aircraft more clearly on radar and allowed them to cut down the distance between approaching aircraft which in return decreased flight time. Also, in the 1960's was the introduction of computer systems to track aircraft instead of ATC using markers and plexiglas boards. The Central Flow Control Facility was introduced in 1970 to help the congested airways in certain regions of the country which later in time became the Air Traffic Control System Command Center. In 1994, Free Flight was introduced courtesy of using GPS. This allowed the pilots to rely on onboard instruments and electronics to keep a safe distance between other aircraft and relieved some of the workload that increased over the years for Air Traffic Controllers.

HOW IT WORKS
Pilots can file flight plans with ATC before taking off or in flight with their desired altitude and route. There are two main types of flight plans: flight plans under Instrument Flight Rules (IFR) and flight plans under Visual Flight Rules (VFR). Flight plans under IFR are used by pilots in order to receive the maximum amount of services from ATC and is required for flights that take place in Instrument Meteorological Conditions (IMC) or Class A airspace. Flight plans under VFR are typically used by pilots to aid Search and Rescue (SAR) crews if an emergency were to occur and when only limited assistance is needed from ATC. ATC can either accept flight plans as they are filed or amend them as needed to ensure separation minimums between aircraft and safety of flight. It should also be noted that ATC can change flight plans depending on their workload. Once a controller confirms the flight plan they will issue pilots a clearance to fly all or a portion of their flight plan.

In a typical scenario, a pilot will first file a flight plan with a Flight Service Station (FSS). When the pilot is ready to depart, he or she will contact a Clearance Delivery Controller for clearance. The Clearance Delivery Controller will instruct the pilot to contact the Ground Controller for taxi instructions to the takeoff runway. Once the pilot is at the designated runway he or she will contact the Local Controller (or Tower Controller) for takeoff clearance. After takeoff a Terminal Controller will guide the pilot out of the aircraft congested area around the airport. The pilot may be handed off to several different Air Route Traffic Control Centers (also referred to Center Controllers) depending on the destination. The Center Controllers handle a vast region covering portions of multiple states handling all IFR traffic. VFR traffic will be handled and provided with assistance, traffic advisories, and other services depending on the Center Controllers workload and equipment capabilities. The pilot is handed off from one center to the next as the aircraft crosses the boundaries of that center's area. When the pilot approaches the airport of intended landing, the Terminal Controller will handle the aircraft towards the airport. The Tower Controller will clear the aircraft to land and a Ground Controller issues the pilot taxi instructions to the parking area.

media type="youtube" key="tizibr_D9p4?fs=1" height="403" width="512" align="center"

CONTROLLERS
There are many different types of controllers in the National Airspace System; each with a designated area of control and objective. Communication among controllers is an essential part of the Air Traffic Control system. While aircraft taxi, takeoff or land, and fly through many different controller's area of control, controllers must efficiently and quickly give the other controllers a heads up and know what the pilot's intentions are.

Clearance Delivery Controllers
Clearance Delivery (CD) Controllers are responsible for coordinating the route structures to be flown and any departure procedures with the pilots. CD Controllers often coordinate with Terminal Controllers or Center Controllers in order to assign aircraft specific route structures in order to ease traffic flow. Pilots contact CD to activate their flight plan. CD Controllers assign pilots their flight plan which could be either be as the pilot filed it or amended as needed. Pilots read back their flight plan in order to assure there is no confusion and the CD Controller confirms the read back is correct. At some smaller airports the CD Controller is often the same as the Ground Controller and operate on the same Ground Controller frequency.

Ramp Controllers
At most major airports with multiple gates and terminals, there may be multiple ramp towers. Ramp controllers give taxi instructions to aircraft arriving and departing terminal gates. They issue engine start and stop clearances, push back clearances, and initial ramp taxi instructions to pilots before they contact Ground Controllers. Ramp Controllers coordinate with Ground Controllers in order to efficiently sort aircraft to and from the ramps.

media type="youtube" key="4kfYxAd4uco?fs=1" height="306" width="509" align="center"

Ground Controllers
Most airports that have an operating control tower usually have a Ground Controller. A Ground Controllers main responsibility is issuing taxi instructions to aircraft that operate about the airport's surface. A Ground Controller may also take on the role of Clearance Delivery at smaller airports. Ground Controllers coordinate with Tower Controllers in order to efficiently handle aircraft to and from runways. Ground Controllers try to move aircraft to runways as quickly and efficiently as possible. This is an essential part in eliminating ramp and departure delays. At some major airports where there is heavy traffic, time slots are sometimes issued in order to effectively handle the traffic load. Ground Controllers work hard to ensure that aircraft get to the runway before their slot time expires. Ground Controllers also handle all airport vehicles. This includes operations and maintenance vehicles. At some major airports Ground Controllers use Airport Surface Detection Equipment Model X (ASDE-X). This provides Ground Controllers a visual display of ground traffic and aids in predicting any incursions of aircraft that might occur. ASDE-X enhances Ground Controller's effectiveness by allowing them to see aircraft are usually not visible from the tower's point of view or aircraft that are not seen because of poor visibility.

Local Controllers or Tower Controllers
Tower Controllers (also referred to as Local Controllers) are located in the Air Traffic Control Tower located on an airport and are responsible for all aircraft that will take off or land. Some airports with a Tower Controller have radar which allows the controller to visualize the aircraft in their airspace. This allows them to properly sequence aircraft for landing, provide traffic advisories to aircraft, and provide aircraft with headings to fly. Tower Controllers ensure the departure path is clear before issuing takeoff clearance to any aircraft. He or she also ensures the runway is clear before issuing landing clearance to any aircraft. Tower Controllers must ensure separation minimums are maintained. With many airports having parallel and intersecting runways, this job can be very tough. Communication with Ground Controllers and Terminal Controllers is key for a Tower Controller. Ground Controllers coordinate with the Tower Controller to find out which runway to send departing aircraft to. Terminal Controllers coordinate with Tower Controllers to see which runways are available for arriving aircraft to land. If runways are not clear by the time another aircraft is arriving to land, the Tower Controller must instruct the landing aircraft to initiate a go around in order to alleviate any potential safety risks. The Tower Controller is also responsible for aircraft that fly through the airspace that is associated with that airport. Some major airports such as the one depicted below, employ terminal controllers that are responsible for only a portion of the airports airspace. This is done because the large amount of traffic that fly through the airspace would be too great for any one person to handle.



Terminal, Approach, and Departure Controllers
Terminal Controllers (also referred to as Approach or Departure Controllers) usually handle the aircraft that are airborne within thirty to fifty miles of a major airport. The Terminal Controllers operate from the Terminal Radar Approach Control (TRACON) facility usually located near major airports. The TRACON utilize radar in order to provide Terminal Controllers a visual display of most aircraft traffic which allows them to enhance their idea of what is going on in the airspace they control. This allows them to properly sequence aircraft for landing, provide traffic advisories to aircraft, and provide aircraft with headings to fly. Terminal Controllers specialize in moving traffic in and out of the terminal environment which consists of many aircraft within the outlying airspace of the major airport or airports. Many smaller airports typically lay either within or under the airspace associated with the major airports. Aircraft are constantly flying in and out of these airports along with the major air carriers, cargo, and charter traffic in and out of the major airports. Terminal Controllers are responsible for safely shuffling traffic to and from many of the smaller airports along with the major airports without compromising safety. Terminal controllers sequence aircraft in order to reduce congestion and risk of collisions. Once an aircraft is handed off from a Center Controller to the Terminal Controller up to fifty miles away from the major airport, the Terminal Controller sequences the aircraft in line behind an another aircraft ahead of the one just handed off from the Center Controller. The Terminal Controller communicates with a Tower Controller to let them know there is an aircraft inbound to the airport for landing. Terminal Controllers usually employ specific routing structures for inbound and outbound traffic called Standard Terminal Arrivals (STARs) and Standard Instrument Departures (SIDs) respectively. STARs and SIDs are specifically designed to file traffic safely while reducing collisions and terrain collisions whether it be mountains, towers, and other features. Terminal Controllers have a demanding workload which consists of keeping track of each aircraft, where it is heading, where it is coming from, keeping surrounding traffic a safe distance away, assisting pilots with any requests they may have and expediting the whole process. Controllers also assign Instrument Approach Procedures (IAPs) to assist pilots in properly aligning with the runway to be used for landing. When weather reduces the outside visibility and pilots can no longer navigate with reference to terrain features, Terminal Controllers typically vector, or give headings to fly, aircraft to a navigation fix or predetermined course which allow pilots to line up with the runway and descend for landing. Terminal Controllers are a great asset to pilots and work very hard to keep safety risks down to a minimum.



ARTCC Controllers or Center Controllers
Air Route Traffic Control Centers, or Center Controllers, mainly assist traffic in climbing or descending to their desired altitudes, keeping traffic flowing to their ultimate destinations, aiding pilots in avoiding adverse weather, assisting pilots with special requests, and much more. When an aircraft crosses the boundaries of the Center Controller's area while en-route, the Center Controller hands the aircraft off to another center controller. This requires communication to effectively provide services to aircraft in a seamless manner. Center Controllers also usually employ radar to see aircraft that lay within their boundaries. This allows them to properly sequence aircraft for landing, provide traffic advisories to aircraft, and provide aircraft with headings to fly.A Center Controller's job becomes more difficult as radar coverage becomes sparse. While most of the contiguous United States is covered by radar, some portions are not adequately covered to provide reliable radar returns. In this scenario Center Controllers remain in contact with pilots and require reporting points in order to keep track of aircraft. Once pilot's begin to reach their destination, Center Controllers hand off pilots to either Terminal Controllers, Tower Controllers, or a Common Traffic Advisory Frequency (CTAF) depending on the whether the destination airport has. Major airports typically have a Terminal Radar Approach Control (TRACON), smaller controlled airports may have a Terminal Radar Service Area (TRSA), which provides similar services as a TRACON, or just a Tower Controller. Uncontrolled airports typically have a CTAF in which pilot's communicate amongst each other to provide and receive traffic advisories as well as let other pilots know of their intentions.



COMPLICATIONS
One of the problems that Air Traffic Control has to contend with for logistics reasoning is the lack of runways and airports in comparison with the 50,000 flights per day. To counteract the issue, the FAA and NASA have developed modern software and implemented a full scale GPS to assist the controllers choreographing all of the flights. This tactic to relieve some of the strain is only a shot term fix. Eventually there will have to be new airports and multiple runways going north to south and etc. One example of this layout is the Hartsfield-Jackson Atlanta International Airport in Atlanta, GA. Another existing issue that is getting more prevelant in the past 10-20 years is the public flying general aviation aircraft. In Florida and other regions of the country, general aviation neighborhoods are becoming popular. This just adds to chaotic traffic in the skies if they are not flying VFR. This is why the FAA is implementing the NextGen System. The main component of this system is the ADS-B: Automatic Dependent Surveillance-Broadcast. The planes that are equipped with this system will allow to broadcast their location, speed and altitude to the ground station and other planes that are equipped this system. This will increase the safety of flying and savings on fuel and carbon emissions. It will also allow the aircraft to be lined up closer to each other on final approach which in return will lead to higher turn around ratio in distributing cargo and passengers. The FAA has projected the commercial airline traffic will double by 2025.

SPECIAL EVENTS
media type="youtube" key="bo1ZtpKqlYw" height="351" width="576" align="center"

After watching the video above, at 9:30 EST roughly, all of the 4,000+ flights dwindled down to none in no time. What the video does not show you is all of the remaining transatlantic flights coming to the United States of America had to be diverted to Gander, Newfoundland, Canada. 39 heavy aircraft transporting passengers and cargo landed at Gander, Newfoundland with 7,000 guests. The only runway turned into a parking aircraft ramp. Systematic and choreographed logistics went out the window.

**REFERENCES**
//Air traffic control//. (n.d.). Retrieved from []_Role/Air_traffic_control/POL15.htm Freudenrich, C. (2011). //How air traffic control works//. Retrieved from http://science.howstuffworks.com/transport/flight/modern/air-traffic-control5.htm  U.S. Department of Transportation, Federal Aviation Administration. (2010). //Administrator's fact book// Washington, DC: Retrieved from []/headquarters_offices/aba/admin_factbook/media/201009.pdf

