General Questions and Answers About ADS-B

Why is the FAA transitioning away from radar and towards ADS-B technology?

ADS-B is an environmentally friendly technology that enhances safety and efficiency, and directly benefits pilots, controllers, airports, airlines, and the public. It forms the foundation for NextGen by moving from ground radar and navigational aids to precise tracking using satellite signals.

With ADS-B, pilots for the first time see what controllers see: displays showing other aircraft in the sky. Cockpit displays also pinpoint hazardous weather and terrain, and give pilots important flight information, such as temporary flight restrictions.

ADS-B reduces the risk of runway incursions with cockpit and controller displays that show the location of aircraft and equipped ground vehicles on airport surfaces – even at night or during heavy rainfall. ADS-B applications being developed now will give pilots indications or alerts of potential collisions.

ADS-B also provides greater coverage since ground stations are so much easier to place than radar. Remote areas without radar coverage, like the Gulf of Mexico and parts of Alaska, now have surveillance with ADS-B.

Relying on satellites instead of ground navigational aids also means aircraft will be able to fly more directly from Point A to B, saving time and money, and reducing fuel burn and emissions.

The improved accuracy, integrity and reliability of satellite signals over radar means controllers eventually will be able to safely reduce the minimum separation distance between aircraft and increase capacity in the nation’s skies.

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What are the ADS-B rules?

The FAA published Federal Regulation 14 CFR § 91.225 and 14 CFR § 91.227 in May 2010. The final rule dictates that effective January 1, 2020, aircraft operating in airspace defined in 91.225 are required to have an Automatic Dependent Surveillance – Broadcast (ADS-B) system that includes a certified position source capable of meeting requirements defined in 91.227. These regulations set a minimum performance standard for both ADS-B Transmitter and the position sources integrated with the ADS-B equipment your aircraft.

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What will make me compliant to fly into ADS-B rule airspace?

See the information on the Equip ADS-B Installation page

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Can I fly under IFR in non-ADS-B airspace if my aircraft is not equipped with ADS-B?

The requirements of the ADS-B rule apply only to the airspace defined in 14 CFR § 91.225, regardless of whether or not the operation is conducted under VFR or IFR. It’s an airspace rule and does not apply to any type of operation outside defined airspace.

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Can I get a one-time deviation from the requirement?

14 CFR § 91.225 subparagraph (g) states:

Requests for air traffic control (ATC) authorized deviations from the requirements of this section must be made to the ATC facility having jurisdiction over the concerned airspace within the time periods specified as follows:

  1. For operation of an aircraft with an inoperative ADS-B Out, to the airport of ultimate destination, including any intermediate stops, or to proceed to a place where suitable repairs can be made, or both. The request may be made at any time.
  2. For operation of an aircraft that is not equipped with ADS-B Out, the request must be made at least one hour before the proposed operation.

Under the above conditions, an aircraft operator may request to deviate from the ADS-B Rule on a case-by-case basis. The ATC facility with jurisdiction of the applicable airspace has discretionary authority to determine whether accommodations for non--ADS-B equipped aircraft can be made. ATC has the authority to deny such requests when deemed appropriate.

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What other surveillance solutions were examined for NextGen and what were the reasons for the decision to implement ADS-B over other alternatives such as Loran enhancement, ground station Mode C transceivers, or Mode S?

The FAA determined the new surveillance system would need to supply these capabilities to lay the foundation for NextGen:

  • Core Surveillance. Perform as well as or better than today’s surveillance system, while also enabling multifunction capabilities. Deliver services cost-effectively.
  • Cockpit Advisory Services. Provide traffic, weather, and database products to improve pilots’ situational awareness and decision-making abilities.
  • Cockpit Critical Services. Enable advanced cockpit display applications that would improve capacity by allowing aircraft to fly safely with less separation and ultimately transfer some separation responsibility from air traffic control to the pilot.

In its analysis, the agency also considered the possibility of doing nothing and retaining all existing radar sites until 2035.

Two alternatives for ground and air-to-air surveillance services were considered along with ADS-B because they met two of the three above criteria (Loran, Mode S, and Mode C technologies did not). These were radar replacement and multilateration. Radar replacement could supply core surveillance and cockpit advisory services, but could not support air-to-air cockpit services and paid back only a fraction of its implementation costs in benefits. Multilateration did not support air-to-air applications. Only ADS-B supported all required and desired capabilities and was found to provide sufficient benefits to the FAA and to aircraft operators within 23 years of implementation.

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ADS-B provides altitude, aircraft number, and vertical air speed. Will it also furnish horizontal air speed?

In fact, ADS-B reports two kinds of altitudes: barometric and geometric. Barometric or pressure altitude is the one pilots know best – this is the altitude that is displayed on the altimeter in the aircraft. Geometric altitude is calculated by GPS (Global Positioning Satellites) as the height of the aircraft above the earth ellipsoid. These two altitudes are not the same, but having both allows for applications that require one or the other as an altitude source and provides a means of verifying correct pressure altitude reporting from aircraft.

ADS-B does not report vertical or horizontal airspeed. Instead, ADS-B reports horizontal and vertical velocity relative to the Earth. This velocity is useful for air traffic control functions and ADS-B applications. Airspeed can be provided by other aircraft sensors.

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When will ADS-B services be available in my area?

ADS-B services are already available across the U.S. including Hawaii, Alaska, Guam, San Juan, and the Gulf of Mexico. A coverage map is available here.

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When do I have to equip?

The rule requires ADS-B Out equipment by January 1, 2020, to operate in designated airspace. If you never fly into ADS-B-designated airspace, then there is no requirement to equip.

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If I fly in airspace that does not require a transponder today, will I still be able to fly there without ADS-B Out?

For the most part, ADS-B Out will be required in the same airspace where transponders are required. However, to be sure of the regulatory requirements it is best to check 14 CFR § 91.225 for ADS-B-designated airspace and 14 CFR § 91.215 for transponder-designated airspace.

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What is the difference between ADS-B Out and ADS-B In?

ADS-B Out refers to an aircraft broadcasting its position and other information. ADS-B In refers to an aircraft receiving the broadcasts and messages from the ground network such as TIS-B and FIS-B. ADS-B In is not mandated by the ADS-B Out rule. If an operator chooses to voluntarily equip an aircraft with ADS-B In avionics, a compatible display is also necessary to see the information. Refer to AC 20-165B for information on ADS-B OUT and AC 20-172B on ADS-B IN installation and certification.

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What are the limitations on ADS-R (rebroadcast) coverage?

ADS-R coverage is provided wherever an ADS-B Out- and ADS-B In-equipped aircraft is within range of an ADS-B ground station. Aircraft will not receive ADS-R if they are not appropriately equipped or within coverage of the ADS-B ground system.

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What is the change in the Technical Standard Order? Change from A to B?

Check Advisory Circular 20-165B as well as TSO-C154c and TSO-C166b for current certification and installation standards for ADS-B Out.

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What is uncompensated latency?

Uncompensated latency is any delay in the time lapse between calculating the aircraft position and broadcasting that information that cannot be compensated for in the avionics by extrapolating the position information of the target.

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Ground Infrastructure

Can I find the latest information on the operational status of a radio station on your website?

Generic information is available on our website.

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What is the range of the ADS-B radio station?

In general, the range would depend on your aircraft’s altitude and any terrain that might block your line of site with the radio station. However, there are also practical limits due to transmitter power and receiver sensitivity. Line-of-sight range to a radio is typically 150 nautical miles or greater.

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How was the ADS-B ground system certified, and how will it be re-certified?

ADS-B systems are certified for aircraft and for vehicles on the ground. For aircraft, there is a requirement for continuing airworthiness certifications that include verifying the proper operation of avionics subsystems.

FAA Technical Operations personnel certify ADS-B for use on air traffic control automation platforms before ADS-B is turned on during Initial Operating Capability (IOC). FAA Technical Operations personnel also perform regularly scheduled certifications of the ADS-B service at each facility where ADS-B is used for air traffic control.

The entire ADS-B system was approved for use throughout the national airspace system when the FAA Administrator made the In-Service Decision in September 2010. Training and operating guidelines will be implemented at each air traffic facility as ADS-B is deployed. Deployment throughout the nation is complete.

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How did implementation of ADS-B affect the airspace in the Gulf of Mexico?

Before ADS-B, surveillance was not available in the Gulf at low altitudes or beyond 200 nautical miles from the coast. Now with ADS-B in place, air traffic control can provide 5-nautical mile separation to low-flying aircraft and to aircraft traversing the Gulf, provided the aircraft have certified ADS-B Out equipage.

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Does the final rule mandate ADS-B Out only?

Yes, only ADS-B Out is mandated, and only within certain airspace. Title 14 CFR § 91.225 defines the airspace within which these requirements apply.

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How will the new ADS-B Out rule affect aircraft operators?

On January 1, 2020, when operating in the airspace designated in 14 CFR § 91.225 (outlined below) you must be equipped with ADS-B Out avionics that meet the performance requirements of 14 CFR § 91.227. Aircraft not complying with the requirements may be denied access to this airspace.

Under the rule, ADS-B Out performance will be required to operate in:

  1. Class A, B, and C airspace.
  2. Class E airspace within the 48 contiguous states and the District of Columbia at and above 10,000 feet MSL, excluding the airspace at and below 2,500 feet above the surface.
  3. Class E airspace at and above 3,000 feet MSL over the Gulf of Mexico from the coastline of the United States out to 12 nautical miles.
  4. Around those airports identified in 14 CFR part 91, Appendix D.

The ADS-B Out rule does not apply in the airspace defined in items 2 and 4 above for any aircraft not originally certificated with an electrical system or that has not subsequently been certified with such a system installed, including balloons and gliders. For additional requirements for using the exception for item 4, please refer to CFR 91.225 section (d) for the requirements.

Please refer to “What are the ADS-B rules?” for more information.

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Will the information broadcast by ADS-B Out be encrypted for security purposes?

ADS-B data can be received by any aircraft, vehicle, or ground station equipped to receive ADS-B. No specific encryption is specified.

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What are FAA ADS-B In broadcast services?

ADS-B In pilot cockpit advisory services consist of Flight Information Service-Broadcast (FIS-B) and Traffic Information Service-Broadcast (TIS-B). These are free services transmitted automatically to aircraft equipped to receive ADS-B In.

FIS-B provides a broad range of textual/graphical weather products and other flight information to the general aviation community. FIS-B is only available on the 978MHz Universal Access Transceiver (UAT) equipment. FIS-B includes the following:

  • Aviation Routine Weather Reports (METARs)
  • Non-Routine Aviation Weather Reports (SPECIs)
  • Terminal Area Forecasts (TAFs) and their amendments
  • NEXRAD (regional and CONUS) precipitation maps
  • Notice to Airmen (NOTAM) Distant and Flight Data Center
  • Airmen’s Meteorological Conditions (AIRMET)
  • Significant Meteorological Conditions (SIGMET) and Convective SIGMET
  • Status of Special Use Airspace (SUA)
  • Temporary Flight Restrictions (TFRs)
  • Winds and Temperatures Aloft
  • Pilot Reports (PIREPS)

TIS-B is an advisory-only service available to both 1090ES and UAT equipment users. TIS-B increases pilots’ situational awareness by providing traffic information on all transponder-based aircraft within the vicinity of the ADS-B In equipped aircraft receiving the data.

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What equipment is required to receive and display ADS-B In?

ADS-B In requires either a 1090 MHz Technical Service Order TSO-C166b or 978 MHz Technical Service Order TSO-C154c, along with a processing system and cockpit display that conforms to ADS-B Technical Service Order TSO-C195b. The new advisory circular for ADS-B In is AC 20-172B.

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I have traffic and weather advisory information now. How are FAA broadcast services different from these?

The main difference is that ADS-B In broadcast services do not require subscription or usage fees. If you choose to equip, ADS-B traffic, weather, and aeronautical information services are available to you free of charge.

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ADS-B In allows operators to get traffic and data-linked geographical weather for free. Is it similar to XM weather some pilots receive now?

Yes. ADS-B’s Flight Information Services-Broadcast (FIS-B) provides all of the information you would get with an XM basic subscription, and more. In fact, at no subscription cost to the user, the ADS-B FIS-B product today is comparable to the mid-to-high-level XM subscription. The FAA currently is discussing with the vendor the possibility of adding even more “no-cost” products to the FIS-B service, such as:

  • Lightning
  • Turbulence NOWcast
  • Icing NOWcast
  • Cloud Tops
  • 1 minute AWOS – uplinked every 10 minutes

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Does TIS-B broadcast primary radar?

For tracks that are initiated with secondary radar, TIS-B will update the track if there is a momentary loss of secondary and only the primary is available. For surface service volumes, TIS-B uplinks primary-only tracks because vehicles operating on airport surfaces may not be equipped with transponders or ADS-B Out.

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Is FIS-B free? Is TIS-B free?

TIS-B is a free service available to aircraft operators equipped with ADS-B Out and ADS-B In. FIS-B is available free to any operator with the ability to receive and display the data that is broadcast on the Universal Access Transceiver (UAT) or the 978 MHz link.

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How do existing traffic display systems integrate with ADS-B?

There are several multi-function displays on the market that interface with ADS-B. Some ADS-B avionics and transponders are produced by the same manufacturer. Before you finalize a purchase, check with an installer or avionics manufacturer to ensure the equipment is able to interface with ADS-B avionics. Refer to AC 20-172B for information on ADS-B In installation and certification guidance.

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Can I install only ADS-B In?

To receive ADS-B In services from the ground network, aircraft must broadcast valid ADS-B Out messages that indicate their ADS-B In capability. Aircraft with “In” only may “piggy back” off an aircraft receiving ADS-R and TIS-B resulting in a partial picture of the traffic.

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Is weather information broadcast on 1090ES?

No. FIS-B provides weather data and it is only available on the UAT or 978MHz link due to bandwidth considerations.

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Contact the FAA Flight Standards ADS-B Office at:
Contact the FAA Aircraft Certification ADS-B Office at:

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