AC 20-172A

U.S. Department of Transportation Federal Aviation Administration

Advisory Circular

Subject: Airworthiness Approval for ADS-B In Systems and Applications Date: 3/23/12 Initiated by: AIR-130 AC No: 20-172A

This advisory circular (AC) provides guidance for the initial and follow-on installations of Automatic Dependent Surveillance – Broadcast (ADS-B) In systems supporting ground and airborne traffic applications. These applications are defined in TSO-C195a, Avionics Supporting Automatic Dependent Surveillance – Broadcast (ADS-B) Aircraft Surveillance Applications (ASA). The applications discussed in this AC are designed to support basic situational awareness as well as the In-Trail Procedure. As more advanced applications mature, this AC will be updated to reflect those added to TSO-C195a.

Susan J. M. Cabler Assistant Manager, Aircraft Engineering Division Aircraft Certification Service

ii

Table of Contents

Paragraph Page

Chapter 1. General Information1

1-1. Purpose1

1-2. Audience1

1-3. Scope1

1-4. Background2

Chapter 2. ADS-B In System Installation Guidance4

2-1. System Overview4

2-2. Equipment Classes4

2-3. ADS-B Applications5

2-4. Cockpit Display of Traffic Information (CDTI)6

2-5. Airborne Surveillance and Separa tion Assurance Processing (ASSAP)8

2-6. ADS-B In Receiver and Antenna8

2-7. Integration Considerations9

Chapter 3. Test and Evaluation11

3-1. General11

3-2. Ground Tests11

3-3. Flight Tests13

Appendix 1. Latency AnalysisA1-1

1. PurposeA1-1

2. AnalysisA1-1

3. Traffic Latency Analysis.................................................................................................. A1 -1

4. Traffic Time of Applicability AnalysisA1-1

5. Own Ship Position Latency AnalysisA1-2

6. Own Ship Position Time of ApplicabilityA1-2

Appendix 2. Symbology Requirements for the CDTIA2-1

1. Traffic Symbols and VariationsA2-1

2. AlertsA2-3

3. TCAS Alert Symbology for TCAS/A SAS Integrated SystemsA2-6

Appendix 3. Definitions and AcronymsA3-1

1. Definitions:A3-1

2. AcronymsA3-9

Appendix 4. Related DocumentsA4-1

1. FAA Documents. ............................................................................................................. A 4-1

2. RTCA, Inc. Documents (RTCA DO) documents:A4-3

3. ARINC Documents:......................................................................................................... A4- 3

4. SAE DocumentsA4-4

5. How to Get Related DocumentsA4-4

iii Table of Contents (Continued)

List of Tables

Table 1. ADS-B In Equipment Classes4

Table 2. ITP Maneuver Criteria15

List of Figures

Figure 1. ADS-B In System Overview2

Figure 2. Traffic Latency Block DiagramA1-2

Figure 3. Own-ship Latency Block Diagram Simple ArchitectureA1-3

Figure 4. Own-ship Latency Block Diagram Alternate ArchitectureA1-3

Figure 5. Basic Directional SymbolA2-1

Figure 6. Basic Non-Directional SymbolA2-2

Figure 7. Directional and Non-directional On-ground Traffic SymbolsA2-2

Figure 8. Basic Surface Vehicle Symbol…………………………………………………….A2-3

Figure 9. Proximate Directional and Non-directional Traffic SymbolA2-4

Figure 10. Directional and Non-directional Designated Traffic SymbolsA2-5

Figure 11. Traffic Advisory SymbolsA2-6

Figure 12. Resolution Advisory SymbolsA2-7

1 Chapter 1. General Information.

1-1. Purpose.

a. This advisory circular (AC) provides guidance material for the installation of ADS-B In technology in aircraft. ADS-B In includes reception of ADS-B, Traffic Information Services-Broadcast (TIS-B) and Automatic Dependent Surveillance – Rebroadcast (ADS-R) messages, but does not include reception of Flight Information Service – Broadcast (FIS-B) messages.

b. The installation of ADS-B In avionics provides the pilot(s) with supplemental information. No existing responsibility is changed by virtue of installation of this equipment and application(s). The situational awareness applications defined in TSO-C195a supplement, but do not replace, a pilot’s see and avoid responsibility, as required by Title 14 of the Code of Federal Regulations (14 CFR) 91.113(b).

c. This AC is not mandatory and does not constitute a regulation. This AC describes an acceptable means, but not the only means, to install ADS-B In equipment. However, if you use the means described in this AC, you must follow it entirely. The term “must” is used to indicate mandatory requirements when following the guidance in this AC. The terms “should” and “recommend” are used when following the guidance is recommended but not required to comply with this AC. A list of definitions and acronyms relevant to this AC can be found in appendix 3.

d. This AC provides guidance information intended for new approvals. This AC is not intended to modify, change or cancel existing equipment design or airworthiness approvals.

Equipment with existing approvals can continue to be installed within the provisions of their original design and airworthiness certification.

1-2. Audience. This AC is for installers of ADS-B In equipment, and can assist in obtaining design approval for installation. The installed design can be approved under a type certificate (TC), supplemental type certificate (STC), including approved model list supplemental type certificate (AML-STC), amended type certificate, or amended supplemental type certificate (ASTC).

1-3. Scope. This AC addresses initial and follow-on installations of ADS-B In systems that comply with TSO-C195a, Avionics Supporting Automatic Dependent Surveillance – Broadcast (ADS-B) Aircraft Surveillance Applications (ASA). Data from a previously approved installation design may be reused to fulfill some of the data requirements for a follow-on installation design as appropriate. For example, the latency analysis between a GPS position source and the ADS-B equipment may be reused on a follow-on installation provided that the hardware and software part numbers for both units are identical. Modifications to previously approved hardware or software must be evaluated to determine data applicability. All installations of ADS-B In should also provide ADS-B Out. Installation guidance for ADS-B Out can be found in AC 20-165, Airworthiness Approval of Automatic Dependent Surveillance - Broadcast (ADS-B) Out Systems.

Installation guidance for flight information service-broadcast (FIS-B) applications that make use of the Surveillance and Broadcast Services (SBS) ground system will be covered in a future AC.

Installation guidance for other FIS-B equipment can be found in AC 20-149, Safety and Interoperability Requirements for Initial Domestic Flight Information Service–Broadcast. A list

2 of related documents can be found in appendix 4 of this AC.

1-4. Background.

a. The ADS-B system, shown in figure 1, is a next generation surveillance technology, incorporating both air and ground aspects that provide air traffic control (ATC) with a more accurate picture of the aircraft’s three-dimensional position in the en route, terminal, and surface environments. The aircraft provides broadcast messages of its identification, position, altitude, velocity, and other information. The ground portion is comprised of ADS-B ground stations, which receive these broadcasts and direct them to ATC automation systems for presentation on a controller’s display. In addition, aircraft equipped with ADS-B In capability can also “see” these broadcasts from other ADS-B equipped aircraft and display them to improve the pilot’s situational awareness of other traffic, both airborne and on the ground. Suitably equipped surface vehicles may also be visible to ADS-B In capable aircraft.

Figure 1. ADS-B In System Overview ATC RADAR Non-ADS-B Target Transponder Reply Track ADS-B 1090 MHz ADS-B on Alternate Link ADS-B on UAT Common Link e.g., 1090MHz ATC ADS-B Ground Station ADS-B Direct Target Sources Traffic Information System Broadcast (TIS-B) ADS-R 1090 MHz TIS-B (1090 and UAT Format)ADS-B Rebroadcast (ADS-R) ADS-B Receiver Airborne Surveillance and Separation Assurance Processor TCAS Position Sensor Barometric Altimeter Other Aircraft Systems Surveillance Tracks Display Data Control Data ADS-B TIS-B ADS-R Reports Antenna Aircraft ADS-B Receiver and Traffic Display Cockpit Display of Traffic InformationSystem Control Data CrewFlight ATC ADS-B Ground Station

b. ADS-B Out refers to an appropriately equipped aircraft broadcasting own-ship information. ADS-B In refers to an appropriately equipped aircraft’s ability to receive and display other aircraft’s ADS-B information and ground station broadcast information, such as

3 traffic information service - broadcast (TIS-B) and automatic dependent surveillance rebroadcast (ADS-R). The TIS-B service provides traffic based on ground surveillance of transponder equipped aircraft. The ADS-R service provides traffic from aircraft equipped with an alternate ADS-B link.

c. There are two ADS-B link options: 1090 extended squitter (1090ES) and universal access transceiver (UAT). The 1090ES equipment operates on 1090 MHz and has performance requirements specified in 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). The UAT operates on 978 MHz and has performance requirements specified in TSO-C154c, Universal Access Transceiver (UAT) Automatic Dependent Surveillance – Broadcast (ADS-B) Equipment Operating on Frequency of 978 MHz.

4 Chapter 2. ADS-B In System Installation Guidance.

2-1. System Overview. ADS-B In refers to an appropriately equipped aircraft’s ability to receive and display other aircraft’s ADS-B information and ground station broadcast information, such as TIS-B and ADS-R. The information can be received by an appropriately equipped aircraft on either of two radio frequency (RF) links: 1090 ES or 978 MHz UAT. The received information is processed by onboard avionics and presented to the flight crew on a display. In this AC, guidance is provided for the display of traffic information while on the airport surface and while airborne. This information supports the applications defined in TSO-C195a. This AC will be updated to add appropriate guidance for additional applications as they mature.

2-2. Equipment Classes. TSO-C195a defines minimum performance standards that provide a basis for installation of ADS-B In equipment in aircraft. The TSO defines three avionics equipment classes: (A) cockpit display of traffic information (CDTI) (surface only); (B) CDTI;

and (C) airborne surveillance and separation assurance processing (ASSAP). Class A equipment is intended to support the display of ADS-B traffic while own-ship is on the surface and moving slower than 80 knots. Class A equipment must deactivate the CDTI when airborne or at speeds greater than 80 knots. Class B equipment supports the display of ADS-B traffic when airborne as well as on the ground. Class C equipment processes ADS-B messages to generate traffic data for a CDTI. Table 1 shows which applications are supported by the three equipment classes. An installation requires both the CDTI and ASSAP functions, which are explained in paragraphs 2-4 and 2-5 of this AC, respectively.

Table 1. ADS-B In Equipment Classes

Criticality Equipment Classes Application Loss of Function Hazardous Misleading Information CDTI (Surface Only) (A) CDTI (B) ASSAP (C) 1 Enhanced Visual Acquisition (EVAcq) Minor Major Not Permitted B1 C1 2 Basic Surface (Runways) Minor Major (> 80 Knots) Minor (< 80 Knots) A2 B2 C2 3 Basic Surface (Runways + Taxiways) Minor Major (> 80 Knots) Minor (< 80 Knots) A3 B3 C3 4 Visual Separation on Approach (VSA) Minor Major Not Permitted B4 C4 5 Basic Airborne (AIRB) Minor Major Not Permitted B5 C5 6 In-Trail Procedures (ITP) Minor Major Not Permitted B6 C6

2-3. ADS-B Applications.

a. ADS-B In avionics enable one or more of the following aircraft surveillance applications: enhanced visual acquisition (EVAcq); basic airborne (AIRB); visual separation on approach (VSA), basic surface (SURF) (runways and taxiways, or runways only); and In-Trail Procedures (ITP). Refer to table 1 to see which applications are supported by the three equipment classes.

b. The basic airborne application (AIRB) displays ADS-B traffic on a plan view (bird's eye view) relative to own-ship. This application is the minimum requirement for installations that implement other applications such as VSA or ITP. Each aircraft symbol displayed conveys position, direction, and altitude information. Optionally, additional information, like identity, may be displayed. The traffic information assists the flight crew in visually acquiring traffic while airborne. This application improves both safety and efficiency by providing the flight crew with enhanced traffic awareness. Installations that provide in flight moving map displays in addition to traffic should comply with TSO-C165, Electronic Map Display Equipment for Graphical Depiction of Aircraft Position.

c. The enhanced visual acquisition application (EVAcq), also displays ADS-B traffic on a plan view (bird's eye view) relative to own-ship. This application is designed to support only the display of ADS-B traffic, including ADS-R, TIS-B, and TCAS derived traffic.

Implementations that include other application classes must use the AIRB application instead.

The traffic information assists the flight crew in visually acquiring traffic while airborne.

EVAcq does not relieve the pilot of see and avoid responsibilities found in 14 CFR 91.113b.

This application is expected to improve both safety and efficiency by providing the flight crew enhanced traffic awareness. Installations that provide in-flight moving map displays in addition to traffic should comply with TSO-C165, Electronic Map Display Equipment for Graphical Depiction of Aircraft Position.

d. The visual separation on approach (VSA) application builds upon the basic airborne application (AIRB). It allows the pilot to select an aircraft to follow on approach. Additional information about the selected aircraft, including range and ground speed, is displayed to enhance the pilot’s situational awareness. The CDTI display is used to assist the flight crew in acquiring and maintaining visual contact during a visual approach. The application improves both the safety and the performance of visual approach operations. The VSA application should not be confused with creating a new approach operation. No operational responsibility is changed when using the VSA application.

e. The basic surface application (SURF) with runways and taxiways displays ADS-B traffic on a plan view (bird's eye view) relative to own-ship, superimposed on a map of the airport surface. This map consists of all runways at supported airports and includes taxiways when that data is available. Aircraft on-ground and in-air as well as properly equipped surface vehicles are differentiated by symbols to aid the pilot in visual acquisition. The surface application improves flight crew situational awareness during taxi, takeoff, and landing phases of flight.

This application reduces the possibility of runway incursion and collision. These installations should also comply with TSO-C165 Electronic Map Display Equipment for Graphical Depiction of Aircraft Position for airport moving map displays. The SURF application with

6 runways only does not display taxiways.

f. The In-Trail Procedure (ITP) application enables aircraft that desire flight level changes in procedural airspace to achieve these changes on a more frequent basis, thus improving flight efficiency and safety. The ITP achieves this objective by permitting a climb-through or descend-through maneuver between properly equipped aircraft, using a new distance-based longitudinal separation minimum during the maneuver. The ITP requires the flight crew to use information derived on the aircraft to determine if the initiation criteria (see Table 2, Section 3-3) required for an ITP are met. The initiation criteria are designed such that the spacing between the estimated positions of ownship and surrounding aircraft exceed the separation minima with acceptable probability throughout the maneuver. ITP requires specific application-unique processing and display parameters. In addition, ITP will require an operations approval by the FAA flight standards organization. Guidance for this operations approval will be contained in a future update to AC 90-114, Automatic Dependent Surveillance- Broadcast (ADS-B) Operations.

g. The displayed ADS-B information addressed by this AC is not intended for maneuvering based solely on presence or absence of traffic on the display. As future applications are fielded, we expect that certain maneuvers may be found to be safe and acceptable. The analysis and safety studies to justify such procedures are not yet completed.

When those activities are concluded and the maneuvers are shown to be safe and acceptable in the national airspace system (NAS), appropriate maneuvers are expected to be allowed based in part on the displayed ADS-B In information. We will revise this guidance accordingly at that time. Operational guidance will be published by FAA flight standards organization.

2-4. CDTI.

a. Displays. The ADS-B In system includes at least one flight deck traffic display (i.e., CDTI) depicting the relative position and related information of ADS-B equipped aircraft in a plan view (bird's eye view). The CDTI display may be presented on a dedicated display or integrated into and presented on an existing display (e.g., electronic flight information system (EFIS), multi-function display (MFD)). CDTI equipment should be compliant with the Class A or Class B requirements of TSO-C195a. Class A equipment supports only the Basic Surface application. CDTI equipment should be installed in accordance with manufacturer instructions.

Installation in the forward field of view (14 CFR 23.1321, 25.1321, 27.l321, and 29.1321) will provide the best situational awareness and support subsequent upgrades to other ADS-B applications. Side-mounted displays are acceptable for the basic situational awareness applications and ITP, but have limited potential to support more advanced applications. The display must be installed such that the crew has an unobstructed view of the display when seated in the normal position. For general installation guidance on displays, refer to AC 25-11A and AC 23.1311-1B.

b. ITP Installations. ITP installations must include a CDTI mounted in the forward field of view or as a side mounted display. The traffic display (plan view) must be visible during the ITP vertical maneuver. It is recommended but not required that a graphical vertical/profile view of the traffic be available for flight crews to aid in assessing initiation criteria. This is particularly helpful in situations where there is a significant angle between the track of the own aircraft and the ITP Traffic aircraft (the angle can be any value less than 45

7 degrees and still be a valid ITP situation). In these cases, relative geometry (ahead of and behind) may not be intuitive.

c. Traffic Symbols. The FAA worked closely with the industry to standardize the ADS-B In symbols and features. The resulting symbols are provided in appendix 2. The traffic display should depict the symbols, features, and information defined in the appendix. However, manufacturers may propose alternate symbols in order to integrate ADS-B with existing flight deck symbology. These alternate symbols will need to be justified by human factors analysis as part of the certification process. Alternate symbol sets are not allowed without additional justification. There is one exception to this guidance. It is acceptable to pair a TSO-C195a Class C ASSAP unit with an existing certified traffic display using legacy symbols (e.g. TCAS, TAS) when either the AIRB or EVAcq application are installed. Minor TSO changes or enhancements, may be made to the previously approved traffic display without requiring the equipment to be made fully compliant to TSO-C195a requirements. This exception only applies to previously approved traffic displays. If any other applications beyond EVAcq or AIRB are installed, the display must be fully compliant with TSO-C195a.

(1) Traffic Symbol and Own Ship Symbol Reference Point. The pilot’s guide for the ADS-B equipment must specify the location of the horizontal position reference point on the traffic symbols and the own ship symbol. For example, this position may be the center of the symbol or the tip of the traffic directional arrow. The own ship horizontal position reference point should be consistent with the existing flight deck philosophy. The traffic and own ship symbols are an abstract representation and are not required to reflect the physical extent of the aircraft. This becomes more evident when implementing the surface application with the underlying airport map.

d. Required Controls. The CDTI control panel may be a dedicated control panel or it may be incorporated into another control, such as a multifunction control display unit (MCDU) or Flight Management Computer (FMC) control display unit (CDU). CDTI controls must be readily accessible from the normal seated position. Pilot controls for the ADS-B In equipment must be provided as follows:

(1) A means to adjust the display range between the minimum and maximum values.

(2) A means to adjust the altitude band between the minimum and maximum values.

(3) A means to adjust the brightness of the display.

e. Optional Controls. The following optional controls may be provided:

(1) A means to select between display of relative and actual altitude.

(2) A means to select at least one traffic element.

(3) A means to select alternate display criteria (e.g., filters and vertical views).

(4) A means to declutter, which removes optional traffic information when display of the information is not desired. If decluttering is implemented,

(a) A means must be provided for the flight crew to control the decluttering.

(b) The flight crew must be able to perform the declutter operation by a simple action.

(c) The flight crew should be able to return to the previous state by a simple action.

(d) If automatic decluttering is implemented, a means should be provided for the flight crew to control the automated decluttering function.

(e) An indication that decluttering is active must be provided.

(5) A means to pan the view. If panning is implemented:

(a) There must be a means to control panning.

(b) There must be a means to return to the original view with a simple action.

(6) A means to designate traffic for an application. For example, equipment may allow a selected aircraft to be designated for the visual separation on approach application.

2-5. Airborne Surveillance and Separation Assurance Processing (ASSAP). The ASSAP subsystem accepts ADS-B reports, TIS-B reports, ADS-R reports, and traffic alert and collision avoidance system (TCAS) tracks (if installed). ASSAP correlates sources, generates tracks, and performs application-specific processing. Surveillance tracks and application-specific alerts or guidance are output by ASSAP to the CDTI function. The ASSAP equipment must be compliant with the Class C requirements of TSO-C195a and should be installed in accordance with manufacturer instructions. TCAS processors track transponder-equipped aircraft.

Therefore, TSO-C195a equipment requires installations with TCAS to provide these tracks to the ASSAP equipment to complete the traffic picture. TCAS in this AC is meant to apply to all versions of certified traffic advisory system (TAS) or TCAS compliant with TSO-C147, TSO-C118, or TSO-C119c. Hybrid surveillance TCAS are included. For aircraft installations without TCAS, the TIS-B service provides tracks of transponder-equipped aircraft.

2-6. ADS-B In Receiver and Antenna. The installation must include a UAT (per TSO-C154c) or a 1090 ES (per TSO-C166b) receiver. Ideally, installation of a dual-band receiver would allow for dual-link interoperability where ADS-R coverage is not provided. The ASSAP equipment may interface with the ADS-B receiver equipment or it may be integrated.

If TCAS is installed, the ADS-B In equipment must contain or interface with the TCAS equipment so that the TCAS tracks may be used. Guidance material concerning the installation of the UAT or 1090ES equipment, and associated antenna(s), is provided in AC 20-165.

2-7. Integration Considerations.

a. System Definition. ADS-B In installations include the ADS-B In receiver, antennas, traffic processor, control panels, and display components. All of these component part numbers must be identified as part of the integrated system. Any change to any of the components’ hardware or software requires evaluation of the potential impact to the ADS-B In function.

b. Equipment Compatibility Requirements. A critical component of the ADS-B In system is the positioning sensor. Compatibility between the sensor and the surveillance processor must be established by the equipment manufacturer(s) and detailed in an installation manual or supplement. Position source compatibility should consider the position source requirements in AC 20-165. Compatibility between all other system components should be documented in an installation manual or supplement.

c. Aircraft Integration with ADS-B In System.

(1) Provide electrical power and grounding in accordance with the manufacturer’s installation manual. Conduct an electrical load analysis to verify that there is adequate power capacity for the ADS-B In equipment.

(2) Ensure that the total latency to receive, process, and display traffic data is less than 3.5 seconds. Ensure that traffic time of applicability is within 1 second of the time of display. Ensure the total latency of own-ship position at the display is less than 3.5 seconds.

Ensure that the own-ship time of applicability is within 1 second of the time of display.

Perform a latency analysis in accordance with appendix 1 to demonstrate compliance. The total latency figures here are to be interpreted to mean when an ADS-B message is received. They do not address data age issues while the system is waiting to receive the next position report for an existing track. Data age and timeout requirements are handled separately for each application in TSO-C195a compliant equipment.

(3) The same position source used to provide own ship data for transmission on ADS-B Out should be used to provide position to the ASSAP equipment. Position sources interfaced to the ASSAP equipment must meet the quality metric requirements in DO-317A, section 2.2.4. Further guidance on integration with ADS-B position sources can be found in AC 20-165. Future applications may require that ASSAP and the ADS-B Out equipment use the same position source. Aircraft manufacturers should plan accordingly to prevent extensive redesign. An alternate position source may be used to provide own ship position to the CDTI display, but the accuracy, latency, and display time of applicability requirements still apply (refer to appendix 1). Provide connections in accordance with the manufacturer’s installation manual.

(4) Follow manufacturer’s instructions for strapping and/or programming of configurable aircraft parameters. Manufacturers are highly encouraged to provide instructions to installers for setting the global navigation satellite system (GNSS) antenna offset parameter during installation. The GNSS antenna offset information can be extremely valuable for ADS-B In surface situation awareness and future surface collision alerting applications on large aircraft with GNSS antenna far from the nose.