Air Traffic Safety Systems Aviation Safety


The mission of Air Traffic Control (ATC) system is to promote the safe, orderly, and expeditious flow of aircraft through the nation's airspace.

Major Milestones of ATC History

June 1956

June 1956- Midair collision over the Grand Canyon in Arizona, killing all 128 occupants of the two airplanes, a TWA Super constellation and a United Airlines DC-7. The accident happened in clear weather under Visual Flight Rules (VFR) in uncontrolled airspace.

December 1960

December 1960- The FAA was only 2 years old when another disastrous midair collision occurred over NYC. a TWA Super Constellation and a United DC-8, both in a holding pattern under Instrument Flight Rules (IFR) collided, killing all aboard. The United aircraft had navigation problems and excessive speed, which could not be detected by NY ATC towers lacking proper surveillance radar equipment.

August 1981

Over 12,000 U.S. Air Traffic Controllers went on strike over labor conditions and were fired by the FAA. It took almost 10 years before overall ATC staffing levels returned to normal.

January 1982

FAA released the first annual NAS plan, a comprehensive 20 year blueprint to modernize the ATC and air navigation systems in the United States.

April 2000

Creation of the FAA Air Traffic Organization (ATO), a performance- based department focusing on efficient operation of the ATC system. This was a major reorganization headed up by an FAA ATO Chief Operating Officer.

September 11, 2001

Two terrorist airline attacks at the World Trade Center in New York City, plus hijackings which damaged the Pentagon in Washington, D.C., and ended in the crash of a fourth aircraft in a Pennsylvania field, caused the FAA to ground all aviation traffic in the country. The Transportation Security Administration (TSA) and Department of Homeland Security were created soon thereafter. Airline traffic decreased for 2 years but eventually recovered.

December 2003

Next Generation Air Transportation System (NextGen) concept was authorized; a new, ambitious multiagency effort to develop a modern air transportation system for the 21st century. This system faces significant challenges changing ATC from a radar based to a satellite based navigation and communication system.

Basic Components of the ATC System


In the United States, the FAA has designated airspace classifications.

Air Traffic Control Services

  • Airport Traffic Control Towers (ATCT)
  • Terminal Radar approach Control (TRACON) Facilities
  • Air Route Control Centers (ARTCCs)

Basic Navigational Aids


VHF Omni directional Range (VOR) and Distance Measuring Equipment (DME) stations which transmit signals along "airways", highways in the sky, to route air traffic.

Instrument Landing System (ILS)

Instrument Landing System (ILS), which is a precision approach and landing aid that normally consists of a localizer, a glide slope, marker beacon, and an approach light system.

Airport Surveillance Radar (ASR)

This is used in conjunction with a transponder radar beacon device, is an approach control radar system used to separate aircraft within the immediate vicinity of an airport; it normally has a maximum range of 60 nautical miles.

GPS Equipment Enhancement

The current U.S. Aviation navigation system is compromised of more than 4,300 ground-based systems whose signals are used by aircraft avionics for en route navigation and landing guidance. Over the next several years, the navigation system is expected to increase its use of GPS satellites, augmented by ground monitoring stations, to provide navigation signal coverage throughout the National Airspace System (NAS). The transition to satellite- based navigation consists of the following:

Global Positioning System

Used for enroute terminal navigation and non precision approaches. GPS is a radio navigation system composed of 24 orbiting satellites that provide extremely accurate three-dimensional position, velocity, track and time at low cost so that even general aviation planes can use it.

Wide Area Augmentation System (WAAS)

Provide enroute/terminal navigation and category (CAT) I precision approaches. WAAS enhances GPS signals to provide more precise location information to an accuracy approximately 3 meters. WAAS is designed to use reference stations covering wide areas throughout the United States to cross check GPS signals and then relay integrity and correction information to aircraft via geostationary communication satellites.

Types of Instrument Approaches

  • Non Precision Approach- This is an instrument approach procedure based on lateral path and no vertical guidance.
  • Precision Approach- This is an instrument approach procedure based on lateral path and vertical guidance.
  • Category I- Category I is a precision instrument approach and landing with a decision height that is not lower than 200 feet above the threshold and vidibility of no less than 1/2 mile.
  • Category II- is a precision instrument approach and landing with a DH lower than 200 feet, but no lower than 100 feet and with a Runway Visual Range of not less than 1200 feet.
  • Category III- is a precision instrument approach and landing with a DH lower than 100 feet or no DH, and with an RVR less than 1200 feet.

Weather Automation Systems

Weather conditions interfere with flight operations and contribute to aviation accidents more than any other factor. The key to reducing weather-related accidents is to improve pilot decision making through increased exchange of timely information. Currently there are a variety of systems that help maintain aviation safety:

  • Integrated Weather System (ITWS)
  • Weather and Radar Processor (WARP)
  • Next Generation Weather Radar (NEXRAD)
  • Terminal Doppler Weather Radar (TDWR)

Integrated Terminal Weather System (ITWS)

Automated weather system that provides near-term (0 to 30 minutes) prediction of significant terminal weather for major terminal locations.

Weather and Radar Processor

Integrated system that receives and processes real time weather data from multiple sources and provides weather information for use by the ARTCCs and Air Traffic Control Command Center (ATCSCC) to support the en route environment.

Next-Generation Weather Radar and Terminal Doppler Weather Radar

NEXRAD is a national network of Doppler Weather Radar to detect, process, distribute and display hazardous weather, providing more accurate weather data for aviation safety and fuel efficiency. This radar has a 250 mile range and the network covers the majority of the domestic en route airspace.

Operational Planning Improvements

To improve flight planning, the FAA has introduced new and improved information services in the areas of Traffic Flow Management (TFM) and flight services that enable collaboration service providers and users sharing the same data and negotiating to find the best solutions to meet operational needs.

Automated Flight Service Stations (AFSSs)

AFSSs provide planning assistance, aviation weather, and aeronautical information to commercial, general aviation and military pilots. The AFSS may be reached by 1-800-992-7433.

Airport Surface Detection Equipment, Model X (ASDE-X)

As frequently noted by the FAA and NTSB, the potential for runway incursions and collisions on taxiways increases each year. To combat this problem, the FAA has deployed ASDE-X at 35 major U.S. airports. This system allows controllers to detect potential conflicts by providing detailed coverage of movement from surface radar, ADS-B sensors aboard aircraft, and aircraft transponders, among other sources.

The Next Generation Air Transportation System (NEXTGEN)

The FAA defines NextGen as an umbrella term for the ongoing and wide ranging transformation of the National Airspace System (NAS). It represents an evolution from a ground based system of air traffic control to a satellite based system of air traffic management (ATM). The current NAS handles 50,000 flights per day and more than 700 million passengers per year.

NextGen Transformational Program

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