2-1 CHAPTER 2. OVERVIEW AND SYSTEM DESCRIPTION
2.1 Overview. Starting with the National Airspace System (NAS)-wide implementation of ADS-B, the FAA has begun to facilitate improvements needed to increase the capacity and efficiency of the NAS while maintaining safety. ADS-B supports these improvements by providing a higher update rate and enhanced accuracy of surveillance information over the current radar-based surveillance systems. In addition, ADS-B enables the expansion of air traffic control (ATC) surveillance services into areas where none existed previously. The ADS-B ground system also provides Traffic Information Service-Broadcast (TIS-B) and Flight Information Service-Broadcast (FIS-B) for use on appropriately equipped aircraft, enhancing the user’s situational awareness (SA) and improving the overall safety of the NAS.
2.2 ADS-B System Description.
2.2.1 ADS-B System Architecture. The ADS-B system architecture is composed of aircraft avionics and an Air Traffic Service Provider (ATSP) infrastructure. Onboard “position source” avionics determine the position of the aircraft, typically by using the Global Navigation Satellite Systems (GNSS) and transmitting this and additional information about the aircraft to receiver stations for use by ATC, to ADS-B In-equipped aircraft, and to other aviation service providers.
2.2.2 ADS-B Operating Frequencies. In the United States, the ADS-B system operates on two frequencies: 1090 or 978 megahertz (MHz). See Chapter 3, Figure 3-1, Automatic Dependent Surveillance-Broadcast Airspace Rule (§ 91.225) Diagram, for airspace and frequency requirements.
2.2.2.1 The 1090 MHz Frequency. The 1090 MHz frequency is associated with current Mode A, C, and S transponder operations. ADS-B information is included in Mode S transponders’ Extended Squitter (ES) transmit messages, and referred to as 1090ES in this AC.
2.2.2.2 The 978 MHz Frequency. ADS-B equipment operating on 978 MHz are referred to as Universal Access Transceivers (UAT) in this AC.
2.2.3 ADS-B Avionics Operating Modes. ADS-B avionics can have the ability to both transmit and receive information.
2.2.3.1 ADS-B Out. The transmission of ADS-B information from aircraft is known as ADS-B Out.
2.2.3.2 ADS-B In. The receipt of ADS-B information by an aircraft is known as ADS-B In.
Note: After January 1, 2020, all aircraft operating within the airspace defined in 14 CFR part 91, § 91.225 will be required to transmit (ADS-B Out) the information defined in § 91.227 using Technical Standard Order (TSO)-C166b, Extended Squitter Automatic Dependent Surveillance-Broadcast (ADS-B) and
2-2 Traffic Information Service-Broadcast (TIS-B) Equipment Operating on the Radio Frequency of 1090 Megahertz (MHz), or TSO-C154c, Universal Access Transceiver (UAT) Automatic Dependent Surveillance-Broadcast (ADS-B) Equipment Operating on Frequency of 978 MHz, avionics.
2.3 ADS-B Broadcast Services. In the United States, ADS-B implementation includes three broadcast services: Automatic Dependent Surveillance-Rebroadcast (ADS-R), TIS-B, and FIS-B. For a detailed explanation of these services, refer to the FAA Surveillance and Broadcast Services Description Document (SRT-047).
2.3.1 ADS-R. Because the ADS-B system operates on two separate frequencies (1090 MHz and 978 MHz), there is a need to translate, reformat, and rebroadcast the information from each frequency to enable aircraft receiving on the other frequency to process and use the other’s information. This process is referred to as ADS-R and occurs within an ADS-B ground station. An aircraft or vehicle that is ADS-B Out and is receiving ADS-R service is known as an ADS-R client. An ADS-B-equipped aircraft or vehicle on the opposite link of the ADS-R client that has its messages translated and transmitted by the ground system is known as an ADS-R target. See paragraph 2.3.5 for ADS-R client qualification criteria.
Note: Aircraft operating on the same ADS-B frequency exchange information directly and do not require ADS-R translation. Aircraft with ADS-B In capability on both UAT and 1090ES do not require ADS-R service.
2.3.2 TIS-B. TIS-B is the broadcast of transponder-based Mode C or Mode S traffic information derived from ATC surveillance systems. TIS-B provides ADS-B In-equipped aircraft with a more complete picture of surrounding traffic in situations where not all aircraft are equipped with ADS-B. An aircraft or vehicle that is ADS-B Out and is receiving TIS-B service is known as a TIS-B client. A non-ADS-B-equipped aircraft or vehicle that has its position transmitted in TIS-B reports is known as a TIS-B target. See paragraph 2.3.5 for TIS-B client qualification criteria.
2.3.3 FIS-B. FIS-B operates on UAT only and provides ADS-B In-equipped aircraft with a suite of advisory-only aeronautical and weather information products to enhance the user’s situational awareness. Additional information on FIS-B and the products available through the service are provided in the Aeronautical Information Manual (AIM) and Advisory Circular (AC) 00-63, Use of Flight Deck Displays of Digital Weather and Aeronautical Information.
2.3.4 Automatic Dependent Surveillance-Same Link Rebroadcast (ADS-SLR). ADS-SLR uses ADS-R to rebroadcast ADS-B messages sent by aircraft on or near a runway; it is available at all airports with an FAA surface surveillance system. Airport structures can block reception of direct aircraft-to-aircraft ADS-B messages on an airport surface, impacting use of ADS-B In systems on an airport surface. This effect is mitigated by ADS-SLR.
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2.3.5 ADS-B Out Requirements for ADS-R and TIS-B. After January 1, 2020, the FAA will no longer use ADS-B data from equipment that does not comply with the performance requirements of either TSO-C166b or TSO-C154c to provide ATC surveillance services.
As such, after January 1, 2020, the FAA will discontinue TIS-B and ADS-R client services NAS-wide for aircraft not equipped with ADS-B Out that complies with the requirements specified in those TSOs or TSO-C199, Traffic Awareness Beacon System (TABS). Operators of ADS-B In-equipped aircraft should refer to paragraph 4.3.2.5 of this AC for additional information on ADS-B Out equipment performance requirements related to TIS-B and ADS-R.
2.4 Use of ADS-B In Information for Traffic Situational Awareness. This paragraph provides guidance on the use of ADS-B In information for traffic situational awareness.
See the appropriate appendices of this AC for guidance on the use of ADS-B In for the more advanced procedures, which may be performed if authorized. There is no specific authorization to use ADS-B In for traffic situational awareness. Installation of ADS-B In equipment is not required for compliance with § 91.225 or § 91.227. However, aircraft owners and operators who choose to voluntarily equip with ADS-B In avionics will achieve greater benefit from the technology through improved traffic situational awareness on the ground and in the air.
Note: This AC only addresses ADS-B In systems installed consistent with AC 20-172, Airworthiness Approval for ADS-B In Systems and Applications, and meeting TSO-C195a (or later revision), Avionics Supporting Automatic Dependent Surveillance-Broadcast (ADS-B) Aircraft Surveillance Applications (ASA).
2.4.1 ADS-B In Systems. Most ADS-B In systems will include a flight deck traffic display depicting the relative position and related information of ADS-B-equipped aircraft presented on a plan view. This traffic display is only one component of the input and output devices collectively known as a Cockpit Display of Traffic Information (CDTI).
The traffic display may be on a dedicated display or integrated into and presented on an existing display (e.g., navigation display (ND) or multifunction display (MFD)). The terms traffic display and CDTI are used interchangeably when the meaning is clear in context. In many installations, a moving map depicting key surface elements of the airport may be displayed when on the ground or within a predefined altitude/distance from an airport while airborne.
Note: ADS-B Traffic Advisory System (ATAS) is an ADS-B In application intended specifically for General Aviation (GA) use that will incorporate an audio traffic alerting capability. There is a configuration in which the display is optional for aircraft that cannot accommodate a display.
2.4.2 Operation. The CDTI will display nearby ADS-B Out traffic and may also display TIS-B traffic, depending on the installation and operating airspace. The display may have functionality to allow the pilot to select a target to obtain additional information that might not be automatically displayed, such as distance from own-ship and groundspeed (GS). The system will also provide range selection and declutter functionality. More
2-4 advanced ADS-B In systems may also include certified functionality to perform ADS-B In procedures described in the appendices of this AC.
Note: For traffic situational awareness, pilots are encouraged to incorporate the display in their normal scan to aid in the early detection of nearby traffic when in visual conditions and to aid in understanding the flow and amount of nearby traffic when in instrument conditions. However, the traffic display is not intended to be used for self-separation or to deviate from an ATC clearance. Should questions arise about a potential conflict with traffic while on an instrument flight rules (IFR) clearance, the pilot should query ATC. Pilots are also cautioned to not allow the display to become a distraction from the primary task of flying the aircraft, or scanning outside for traffic. Finally, pilots are cautioned against unnecessarily communicating on the ATC frequency about traffic observed on the traffic display.
2.4.3 Limitations. Pilots should understand the proper use and limitations of their equipment and should adhere to the following:
2.4.3.1 Only use the traffic display to supplement what can be seen out the window (OTW), except when authorized to conduct ADS-B In operations described in the appendices of this AC. Pilots must always conduct OTW scans to see and avoid as required under § 91.113(b).
2.4.3.2 Unless specifically certified for the function, the traffic display is not intended for collision avoidance or self-separation.
2.4.3.3 Not all ground and airborne traffic will appear on the traffic display. The traffic display can only display properly equipped ADS-B Out traffic broadcasting on the received frequencies, and, depending on the operating location, ADS-SLR, ADS-R, TIS-B, and/or Traffic Alert and Collision Avoidance System (TCAS) (if installed) traffic. Additionally, the completeness of the traffic situational awareness information is affected by range, signal quality, and proper installation and function of the ADS-B Out system on the traffic aircraft.
2.4.3.4 Unless initiated by the controller, pilots should typically not use the call sign or Aircraft Identification (ACID) of observed traffic in radio communications, as this could create confusion for both ATC and pilots monitoring the frequency.
2.4.3.5 In multipiloted aircraft, establish and comply with crew coordination procedures on the use of the CDTI and ADS-B In information to minimize head-down time.
2.4.3.6 Use of the traffic display does not change pilot or controller responsibilities.
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2.4.3.7 If at any time the presented information becomes unreliable, inoperative, or a distraction, disregard the information presented on the traffic display.
2.4.3.8 In TCAS-equipped aircraft, ADS-B In traffic display information does not change existing procedures for response to a traffic advisory (TA) and/or Resolution Advisory (RA).
3-1 CHAPTER 3. OPERATIONAL CONSIDERATIONS
3.1 U.S. ADS-B Airspace and Equipment Performance Requirements. After January 1, 2020, unless authorized by air traffic control (ATC), all aircraft operating in the airspace specified in 14 CFR part 91, § 91.225 must meet the equipment performance requirements defined in § 91.227. This chapter describes both the airspace and equipment performance requirements of §§ 91.225 and 91.227. Operators should consider the need to access ADS-B-required airspace and the performance requirements of that airspace when equipping for compliance with §§ 91.225 and 91.227.
3.1.1 Inside Class A Airspace. Operations in Class A airspace must:
1. Meet the equipment performance requirements in Technical Standard Order (TSO)-C166b, Extended Squitter Automatic Dependent Surveillance-Broadcast (ADS-B) and Traffic Information Service-Broadcast (TIS-B) Equipment Operating on the Radio Frequency of 1090 Megahertz (MHz) (1090ES).
2. Meet the requirements of § 91.227.
Note: Although TSO-C166b incorporates standards for TIS-B equipment, TIS-B equipage (ADS-B In) is not required for compliance with §§ 91.225 and 91.227.
3.1.2 Outside Class A Airspace. Operations within airspace defined in § 91.225, but outside Class A airspace must:
1. Meet the requirements of § 91.227; and
2. Meet the performance requirements in:
• TSO-C166b (1090ES); or
• TSO-C154c, Universal Access Transceiver (UAT) Automatic Dependent Surveillance-Broadcast (ADS-B) Equipment Operating on Frequency of 978 MHz.
Figure 3-1. Automatic Dependent Surveillance-Broadcast Airspace Rule (§ 91.225) Diagram FL 600 18,000 MSL CLASS A | ADS-B 1090 ES Required 2,500 AGL ADS-B Not Required CLASS E | 10,000 MSL and above ADS-B Required
CLASS E Required ADS-B CLASS C CLASS B 10,000 MSL 3,000 MSL ADS-B ADS-B Required Required 12NM From Coastline 10,000 MSL Surface 10,000 MSL Surface Mode C Veil ADS-B Required Gulf of Mexico: 10,000 MSL Surface © AGL: Above Ground Level; FL: Flight Level; MSL: Mean Sea Level; NM: Nautical Miles
3.2 Exceptions to Airspace Requirements. The requirements of § 91.225(b) do not apply to any aircraft that was not originally certified with an electrical system or that has not subsequently been certified with such a system installed, including balloons and gliders.
The FAA has previously determined that the same aircraft excluded from the transponder requirement are excluded from the ADS-B Out equipage. Accordingly, an aircraft that subsequently has been installed with batteries or an electric starter would not be required to equip for ADS-B Out. These aircraft may conduct operations without ADS-B Out in the airspace specified in § 91.225(d)(2) and (4). However, for other aircraft without ADS-B Out, § 91.225(g) requires ATC authorization prior to operation in ADS-B Out-required airspace.
3.3 Traffic Awareness Beacon System (TABS). Operators of aircraft exempt from carrying a transponder or ADS-B equipment may wish to consider installing a TABS device (refer to ISO-C199, Traffic Awareness Beacon System (TABS)). TABS devices do not meet the transponder or ADS-B requirements defined in §§ 91.215 and 91.225, respectively.
However, they will allow TABS-equipped aircraft to be electronically "visible" to aircraft equipped with Traffic Alert and Collision Avoidance Systems (TCAS), Traffic Advisory Systems (TAS), and ADS-B In systems. TABS-equipped aircraft that are broadcasting an ADS-B In capability will also become TIS-B clients.
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4-1 CHAPTER 4. OPERATING PROCEDURES
4.1 General Operating Procedures. This chapter describes the general procedures for ADS-B Out operations in accordance with 14 CFR part 91, §§ 91.225 and 91.227. All operators should use this information when planning and conducting operations requiring ADS-B Out performance.
4.2 Operator Familiarity of the Installed ADS-B System.
4.2.1 System Operation Familiarity. All operators should use the applicable Airplane Flight Manual (AFM), Aircraft/Airplane Flight Manual Supplement (AFMS), Rotorcraft Flight Manual (RFM), Rotorcraft Flight Manual Supplement (RFMS), pilot’s operating handbook (POH), or other required operating handbooks or manuals to become familiar with the proper operation of the installed ADS-B system and any procedures expected of the user for indications of reduced performance or failures within the system.
4.2.2 Understanding Failure Indicators Within the System. Because many ADS-B system installations will be upgrades to existing transponders (Mode S), there may be limited ability to indicate ADS-B failures. Mode S transponders with ADS-B functionality may indicate a device failure (loss of transponder/ADS-B) and input failures (loss of position source, such as the Global Navigation Satellite System (GNSS)) with the same indicator light. Operators should refer to their AFM, AFMS, RFM, RFMS, POH, and other handbooks and manuals for information on the differences between device failures and function failures and the implications and procedures associated with each failure type. In particular, normal GNSS signal interference on the ground caused by nearby obstacles, such as a large hangar, may be incorrectly interpreted as a failure of the ADS-B system.
Moving the aircraft clear of obstructions may be all that is needed to clear an indicated malfunction caused by GNSS multipath signals.
4.2.3 Transponder Operation and ADS-B Transmissions. For ADS-B system installations integrated within a transponder that share control features, operators should be aware that disabling the transponder may also disable ADS-B transmissions, as well as result in a loss of Secondary Surveillance Radar (SSR) services and Traffic Alert and Collision Avoidance System (TCAS)/TCAS II operation, if so equipped.
4.3 ADS-B Equipment Operations (U.S. Airspace).
4.3.1 Transmit Requirements. In accordance with § 91.225(f), each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times, unless authorized by the FAA or directed by air traffic control (ATC). This equipment operation requirement pertains to all phases of flight operation, including airport surface movement area operations. Pilots should select the transponder mode that enables the altitude reporting and ADS-B Out transmissions any time their aircraft is positioned on any portion of an airport movement area.
Note: Aircraft must comply with the appropriate Technical Standard Order (TSO) performance requirements when transmitting ADS-B data.
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4.3.1.1 Departures. Select the transponder mode that allows altitude reporting, and enable ADS-B Out during pushback or taxi-out from parking spot. Select TA or TA/RA (if equipped with TCAS) when taking the active runway.
4.3.1.2 Arrivals. After clearing the active runway, if TCAS-equipped (TA or TA/RA), select the transponder to altitude reporting mode, and maintain ADS-B Out transmissions. Select “STBY” or “OFF” for the transponder and ADS-B only upon arriving at the aircraft’s parking spot or gate.
4.3.1.3 Formation Operations. ATC uses established transponder and ADS-B transmission procedures when participating in formation operations. Per the Aeronautical Information Manual (AIM) paragraph 4-1-20, if the formation flight is receiving ATC services, pilots can expect ATC to direct all non-lead aircraft to “STOP SQUAWK,” and should not do so until instructed. For visual flight rules (VFR) formation flights not receiving ATC services, ATC directs that only the lead aircraft should squawk the assigned beacon code (1200). All other aircraft should disable transponder and ADS-B transmissions once established within the formation.
4.3.1.4 Inoperative ADS-B Out. For operations with inoperative ADS-B Out comply with the requirements of § 91.213 as appropriate for your aircraft. If you intend to operate in airspace described in § 91.225, refer to paragraph 4.3.3 and comply with § 91.225(g)(1).
4.3.2 Equipment Qualification Requirements. In order to operate an aircraft in airspace defined in § 91.225, the ADS-B Out equipment installed, and its connected or internal position source, must meet the performance requirements of the applicable TSOs and meet the requirements of § 91.227. Since § 91.225 requires the equipment components be installed, portable ADS-B Out equipment, including system components and antennas, does not comply with the rule. Operators should also note that FAA regulations require installed equipment to function as intended. Under 14 CFR part 21, installed equipment need not be manufactured under a TSO authorization, but must be approved or qualified according to the type of aircraft as follows:
4.3.2.1 Type-Certificated Aircraft. ADS-B Out systems and equipment (including the connected position source) installed or used in type-certificated aircraft must have a design approval issued under part 21 or must be installed by field approval, if appropriate. AC 20-165, Airworthiness Approval of Automatic Dependent Surveillance—Broadcast OUT Systems, provides guidance on installation of ADS-B Out systems. FAA Policy Memorandum, Installation Approval for ADS-B OUT Systems, dated 2016, provides information on how ADS-B systems may be installed by field approval.
4.3.2.2 Special Light-Sport Aircraft (SLSA). Equipment installed on SLSA must be installed in accordance with an applicable consensus standard and must be authorized by the aircraft’s manufacturer or a person acceptable to the FAA (refer to part 21, § 21.181).
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4.3.2.3 Experimental Aircraft, Including Experimental Light-Sport Aircraft (ELSA).
4.3.2.3.1 For experimental category aircraft, including ELSA, there is no FAA approval required for the ADS-B Out system installation. However, to protect all users of the National Airspace System (NAS), it is essential for all aircraft, including experimental and ELSA, to install equipment that has been adequately designed and tested to meet the equipment’s intended functions of supporting safe ATC separation services and providing accurate traffic awareness to other aircraft. To meet this requirement, owners of these aircraft may elect to install equipment manufactured under a TSO authorization, in accordance with the installation instructions provided by the manufacturer.
Alternatively, owners of these aircraft may elect to install equipment that are not approved under a TSO authorization. For non-TSO equipment, the owner should obtain installation instructions that include a statement of compliance from the applicable avionics manufacturer(s). To qualify non-TSO equipment as compliant for operations in ADS-B airspace defined in § 91.225, the statement of compliance should indicate that when installed in accordance with the installation instructions, the equipment complies with all requirements of § 91.227, and with the performance requirements of the appropriate TSO. While the statement of compliance is important in equipping the aircraft, per § 91.225, correct installation is critical for the equipment to operate properly.
4.3.2.3.2 Owners of experimental aircraft should retain the installation instructions from the equipment supplier, including the statement of compliance, in the aircraft records to support the equipment’s compliance with the requirements of §§ 91.225 and 91.227, and to assist in resolving in-service issues if necessary.
4.3.2.4 All Aircraft—Importance of Proper Installation. Experience with FAA compliance monitoring of ADS-B Out-equipped aircraft to date has revealed that a large percentage of equipped aircraft have deficiencies with ADS-B Out system performance following initial installations. Many of these deficiencies have been attributed to improper installation and incorrect system configuration. Therefore, the FAA considers it particularly important for equipment manufacturers to provide installation instructions that are as clear and easy to follow as possible and revise these instructions when deficiencies in the instructions are discovered. Installers should adhere to the manufacturer’s installation instructions and employ practices that consistently result in ADS-B Out system installations that fully comply with § 91.227 equipment performance requirements.
4.3.2.5 All Aircraft—ADS-B Out Equipment Performance and FAA Monitoring.
4.3.2.5.1 The ADS-B Out rule does not impose additional continued/recurrent airworthiness inspection requirements for applicable equipment. Therefore,
4-4 owner/operators of ADS-B Out-equipped aircraft should ensure continued compliance of applicable equipment performance requirements following initial installation or any subsequent alteration to the system.
Note: Transponder-based ADS-B Out systems (i.e., 1090ES) are still required to meet the requirements of § 91.413.
4.3.2.5.2 The FAA continuously monitors the equipment performance of all ADS-B Out-equipped aircraft operating in U.S. airspace for compliance of regulatory requirements specified in § 91.227. Applicable equipment performance monitoring is conducted by a tool known as the ADS-B Performance Monitor (APM).
4.3.2.5.3 The APM collects data transmitted by ADS-B Out-equipped aircraft monitored on the surface and airborne. The APM applies established compliance criteria to collected data for more than 40 individual equipment performance checks, assembles relevant information into a flight record, and identifies exceptions to applicable regulations to support various internal and external reporting requirements. Aircraft identified by the APM with exceptions are referred to as non-performing equipment (NPE).
4.3.2.5.4 While the term NPE is generally used to describe aircraft with ADS-B Out equipment performance exceptions, certain pilot actions can result in NPE conditions. Such pilot actions may include the following:
1. Movement of aircraft on the surface (under its own power) or while airborne with ADS-B Out equipment turned off;
2. Operating with a non-conforming or unauthorized (local call-sign) flight identification (FLT ID) code;
3. Operating with a FLT ID code that does not correspond to the code filed on an associated flight plan (FP) (as applicable);
4. Operating with barometric altitude reporting off (when not directed to do so by ATC);
5. Operating a Universal Access Transceiver (UAT) transponder-dependent device with the transponder turned off (no barometric altitude or Mode 3/A code present in ADS-B messages); and
6. Operating ADS-B Out equipment in any manner contrary to applicable regulations.
4.3.2.5.5 As discussed in paragraph 4.2, pilots should be familiar with the operation of ADS-B Out equipment, including any associated failure indications provided by the system. It is important for pilots to understand that most ADS-B failure indications are limited to system component failures; and indications associated with equipment performance required by regulation are not provided.
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4.3.2.5.6 To enable public access to ADS-B equipment performance data needed for owner/operators to verify compliance with § 91.227 requirements, the FAA provides a free, web-based service called the Public ADS-B Performance Report (PAPR) at https://adsbperformance.faa.gov/PAPRRequest.aspx.
Additional information on the PAPR service can be found at https://www.faa.gov/nextgen/equipadsb/.
4.3.2.5.7 The FAA recommends that owner/operators of ADS-B Out-equipped aircraft verify equipment performance through periodic use of the PAPR request service, especially following initial equipment installation, modification, or maintenance of existing ADS-B Out systems (including component software updates/changes).
4.3.2.6 Handling of Aircraft with Non-Performing Equipment (NPE).
4.3.2.6.1 When ADS-B Out equipment performance becomes deficient during flight, ATC may direct the pilot to discontinue ADS-B Out transmissions pursuant to § 91.225(f)(2). The pilot should comply with the procedures established for that aircraft or notify ATC if unable. If necessary, ATC may direct the aircraft to exit § 91.225 airspace.
4.3.2.6.2 FAA flight monitoring has shown that aircraft engaged in aerobatic and agricultural operations may fail to meet applicable equipment performance requirements due to maneuvering that exceeds the design limits of the installed GNSS equipment. Aircraft identified by the APM with exceptions to § 91.227 resulting from maneuvering characteristics of aerobatic and/or agricultural operations are not considered NPE by the FAA. When not actively engaged in aerobatics or agricultural operations (e.g., when transiting to and from applicable areas of operation), these aircraft are expected to meet ADS-B Out equipment performance requirements.
4.3.2.6.3 In late 2017, the FAA published a notice (82 FR 60302) to the Federal Register announcing changes to ADS-B services including the Traffic Information Service-Broadcast (TIS-B) (refer to Docket Number FAA-2017-1194, Change to Automatic Dependent Surveillance Broadcast Services, at https://www.federalregister.gov/). These changes included implementation of a filter within the FAA ATC automation system to prevent processing of data transmitted by certain NPE aircraft. Application of the filter is enabled by restricting use of the 24-bit International Civil Aviation Organization (ICAO) address (Mode S code) transmitted from NPE aircraft and managed through a list referred to as the No Services Aircraft List (NSAL). NPE aircraft on the NSAL cannot be provided ATC services via the ADS-B data network and do not meet the equipment performance requirements necessary to qualify for TIS-B client services. Owner/operators of aircraft on the NSAL must seek authorization from ATC to operate in the airspace specified by § 91.225.