Air Traffic Control
ATC Facilities
The United States air traffic control (ATC) system is managed and operated by the Federal Aviation Administration (FAA), an agency of the U.S. Department of Transportation. The government developed the ATC system primarily to maintain safe separation of aircraft arriving in, departing from and flying over the United States. Secondarily, it is an air navigation provider’s job to keep air traffic moving as efficiently as possible throughout the system. In short, ATC is aviation's traffic cop, working to ensure that aircraft fly safely through the airspace and that traffic moves in an orderly fashion with minimal delay.
The U.S. ATC system is the safest and oldest ATC system in the world. Today our system is prone to capacity and delay problems affecting both passengers and shipments. We continue to rely on technologies and procedures developed decades ago that consume tremendous amounts of capital resources. The architecture of the ATC system is what requires the most urgent modernization.
There are several types of ATC facilities. These include the ATC towers (ATCTs) familiar to most travelers, terminal radar approach control facilities (TRACONs), air route traffic control centers (ARTCCs)
The Air Traffic Control System Command Center (ATCSCC) (previously known as Central Flow Control Facility) was established in 1970 to prevent pockets of congestion from disrupting the National Airspace System (NAS). Located in Herndon, VA, the FAA Command Center anticipates NAS bottlenecks and responds with a management plan for aircraft transiting constrained airspace
Air traffic tower personnel control airborne aircraft and specifically landings and takeoffs in the immediate vicinity of the airport (generally 2-5 nautical miles) and ground movements of aircraft and vehicles transiting to and from runways, taxiways and ramps. The FAA bases its decision to build and operate a tower on the number of aircraft operations at a given airport. More than 500 U.S. airports currently have such towers.
TRACONs generally control aircraft in a 30-50 mile radius from the airport from the surface up to 11,000 feet and may control more than one airport. There are currently 168 combined ATCT/TRACONs. For example, a single TRACON handles multiple airports and all of the traffic approaching and departing from the entire New York-metro area. FAA is in the process of consolidating TRACONs to improve efficiency.
The 21 ARTCCs issue clearances/instructions for airborne aircraft, and provide services to aircraft at many small airports without ATC towers. Their job is to keep track of aircraft while they are en route or during the high-altitude cruise phase of their flights. They are located in Albuquerque, Anchorage, Atlanta, Boston, Chicago, Cleveland, Denver, Fort Worth, Houston, Indianapolis, Jacksonville, Kansas City, Los Angeles, Memphis, Miami, Minneapolis, New York, Oakland, Salt Lake City, Seattle and Washington, D.C.
Surveillance Systems
ATC primarily uses radar to keep track of aircraft flying over the United States with centers utilizing radar systems with ranges of up to 200 miles. Consolidating the numerous radar systems require costly automation to consolidate and effectively display the data. In the future, satellites are expected to replace ground-based radar as the primary means of tracking airplanes.
Communications
Flight crews and air traffic controllers communicate by radio using VHF frequencies between108 and 137 megahertz. Pilots tune to the frequency of the controller tracking their flight and switch frequencies as they move through the system and are handed off from one controller to the next.
A Typical Flight
From the standpoint of ATC, all airline flights begin with the flight plan, which spells out the route the flight crew plans to follow, alternative airports the crew would use in the event of an aircraft emergency or a problem at the intended destination, as well as the amount of fuel onboard the aircraft. The aircraft dispatcher submits the flight plan to ATC prior to the departure of the flight. Many airlines that fly the same routes every day keep flight plans stored in the FAA host computer and merely activate them through their dispatch systems prior to flight. In any event, a flight plan provides crucial information to ATC about what a particular crew intends to do.
Once the pilots have completed their preflight planning, aircraft inspections, and have settled into the cockpit, they make their first call to ATC. Typically this call is made to clearance delivery, which reads back to the crew the filed ATC flight plan and instructions the crew can expect from takeoff to landing. Ideally, but not always, this information matches the route filed in the flight plan. ATC sometimes has system constraints or traffic-management initiatives in place that the flight crew may not be aware of, at which point ATC would give pilots new instructions before or during a flight.
When the flight crew is ready to depart, it contacts ground control for permission to leave the gate. Once an aircraft leaves the gate area and begins to taxi, it comes under the jurisdiction of FAA ground control.
The tower controller assumes full control of the aircraft as soon as it reaches the end of the runway it will use for takeoff. When the runway is clear, the tower grants permission for takeoff. It also instructs the crew on the heading, or direction, it should follow immediately after takeoff.
When safely airborne, tower control hands off the aircraft to departure control, which oversees the flight as it climbs away from the airport and enters the en route airspace. Given the speed and climb capabilities of modern jets, this may only take a few minutes. Departure control then turns over the flight to an en route center.
All of these and subsequent handoffs are accomplished by radio. The controller handing off the flight instructs the crew to contact the next level of ATC surveillance, and gives the crew the necessary radio frequency. Once contacted, a receiving controller acknowledges radar contact with the flight crew and issues instructions for heading and altitude.
Depending on where the plane is going, it may be handed off many times during the course of its flight, from one en route controller to another. En route controllers are assigned to specific sectors or areas in which they work to maintain safe separation of aircraft.
Aircraft separation standards vary according to circumstances. When aircraft are cruising at high speeds in en route airspace, the standard is five miles of horizontal radar separation or 1,000 feet of vertical separation. When aircraft are moving at much slower speeds as they depart or approach the airport terminal area, the standard is three miles of horizontal radar separation.
As an aircraft approaches its destination airport and begins its descent, the flight crew is instructed to contact approach control. An approach controller will issue instructions to the crew to blend the aircraft into the flow of other aircraft arriving at the airport. As soon as the crew is on its final, straight-in approach, the approach controller hands the aircraft off to the airport tower, which grants final clearance to land and monitors the aircraft until it completes its landing and exits the runway. A ground controller then directs the aircraft to its gate.
Flight Rules
While all commercial airlines are controlled every step of the way, the same level of positive control does not always extend to general aviation aircraft. These aircraft can, and often do, fly at 18,000 feet (FL180) and below, without the benefit of ATC instruction. Since aircraft climb and descend at an angle, the airspace controlled by ATC in the airport terminal area resembles the conical shape of a giant, upside-down wedding cake over the airport proper.
Instrument flight rules (IFR) govern how aircraft must fly in bad weather and low visibility. To fly commercial aircraft or to fly IFR, the flight crew or pilot must be instrument-rated, meaning they are proficient at navigating and flying using cockpit instruments only, without the benefit of good visibility out of the cockpit windows. Commercial airline flights by federal regulation always file IFR flight plans, regardless of weather.
General aviation pilots must file an IFR flight plan whenever a flight cannot be operated under visual flight rules (VFR). General aviation aircraft may fly under VFR when weather and visibility are good. They do not have to file a flight plan nor communicate with ATC, unless they choose to operate into or out of an airport with a control tower. Under VFR, pilots are responsible for maintaining adequate separation from other aircraft, which is why these rules sometimes are called the see and be seen rules.
Airport and Airway Trust Fund
In 1970, Congress created the Airport and Airway Trust Fund (AATF) to pay for improvements to airports and the ATC system, such as new runways and taxiways, control towers, landing aids and radar systems. In the years since, Congress also has authorized the use of trust fund money for FAA operating costs, such as the salaries of controllers.
The money in the fund comes from taxes and fees paid primarily by airlines, air travelers and shippers. Congress has raised the taxes numerous times. General and business aviation contributes increasingly to congestion but accounts for a minimal and disproportionate share of trust fund revenues.
Delays, Modernization and Corporatization
Because ATC is involved in the movement of all commercial aircraft, the capabilities and efficiencies of ATC have a direct bearing on airline schedule performance and customer experience. An equipment glitch or personnel shortage at an ATC facility, for example, usually means that the flights it handles will be delayed. Bad weather, of course, is the primary cause of most back-ups, but deficiencies in the National Airspace System itself can also play a major role in airline delays.
The FAA projects that U.S. airlines will carry more than one billion passengers by 2021 with enplanements rising an average of 2.7 percent per year after a drop in 2009. In order to prepare for this growth, the aviation community will need to invest in the Next Generation Air Transportation System (NextGen); the successor to today’s antiquated ATC system. In 2008 every minute of aircraft delay cost the industry more than $74, for an annual system total of nearly $9.5billion.
When air travel and air cargo service soared following deregulation, the FAA began a massive modernization effort intended to bring the ATC system up to where it needed to be to handle air traffic efficiently. However, the effort quickly bogged down and remains troubled, with little to show in terms of reducing airline delays.
The concept of a federal corporation to run ATC, more along the lines of a modern business, was advanced by the airlines in the mid-1980s. However, the idea met considerable opposition at that time, and again in 1994, when the Clinton administration advanced its own version of the concept. There has been no recent attempt to corporatize. The Civil Air Navigation Services Organization (CANSO) represents dozens of air navigation service providers (ANSP) that have been commercialized, meaning they are separate from the nation’s aviation safety regulators and are financially self-supporting from fees and charges paid by their aviation customers.
Chapter 8
Chapter 10