r- + + ----, second by the system prior to displaying that traffic. The actual estimate for each individual piece of traffic will vary as the received ADS-B messages arrive asynchronously. The analysis must demonstrate that this variation is handled appropriately. The analysis must also demonstrate that any variation in the latency due to processes within the equipment chain does not cause the time of applicability to violate the 1 second tolerance. If different vendors’ equipment is paired together to create a complete system, latency performance data for each system component must originate with the component manufacturer. Reverse engineering another vendor’s latency performance is not an acceptable means of compliance.
Manufacturers are encouraged to include their individual component latency performance in an installation manual to facilitate proper ADS-B system integrations.
Figure A-1. Traffic Latency Block Diagram ASSAP CDTI Flight CrewADS-B Receiver Bottom Top Antenna ADS-B Reports TIS-B Reports ADS-R Reports
D E F G
0.5 s 2.5 s 0.5 s Correlated Best Tracks Display Data Crew Inputs Antenna
5. Own-Ship Position Latency Analysis.
Refer to Figures A-2 and A-3 which depict block diagrams of two potential implementations of ADS-B In system architectures with recommended latency budgets allocated to each block. For either architecture, the ASSAP equipment must receive the own-ship position data with less than 600 ms of compensation error and less than 1 second of total latency. For this portion of the analysis, total latency starts at the time of measurement of the position source (A3) and ends when ASSAP has received the complete position update (B3). Own-ship total latency at the time of display (G) must not exceed 3.5 seconds.
6. Own-Ship Position Time of Applicability.
Demonstrate by analysis that the own-ship position displayed to the flight crew has been estimated forward to be within 1 second of the time of display. The 1 second tolerance must include any compensation error present in the system between interfaces A3 and G. Determine the total latency from the position source time of measurement (A3) to the time of display (G).
This latency will depend on the path of own-ship position data and vary by system architecture.
Refer to Figures A-2 and A-3 for examples of two potential architectures. The analysis must demonstrate that any variation in the latency due to processes within the equipment chain does not cause the time of applicability to violate the 1 second tolerance. If different vendors’ 24
r- + + ~ L - -- - --~ - T ~ _L 05/20/15 AC 20-172B equipment is paired together to create a complete system, data for each system component must originate with the component manufacturer. Reverse engineering another vendor’s latency performance is not an acceptable means of compliance. Manufacturers are encouraged to include their individual component latency performance in an installation manual to facilitate proper ADS-B system integrations.
Figure A-2. Own-Ship Latency Block Diagram Simple Architecture A3 B3 F G
1.0 s 2.0 s 0.5 s Antenna ASSAP CDTI Flight CrewGNSS Receiver PVT Ownship Position Display Data Crew Inputs Figure A-3. Own-Ship Latency Block Diagram Alternate Architecture A3 B3 F G
1.0 s 0.5 s Antenna Display Correlated Data Best Tracks PVT FAntenna A3 ASSAP CDTI Flight CrewGNSS Receiver PVT GNSS Receiver Crew Inputs
1.0 s 25
Appendix B Symbol Requirements for the CDTI
1. Traffic Symbols and Variations.
The “basic” traffic symbol is used to depict airborne traffic. Traffic symbols can be modified from the basic symbol to provide special status information, such as on-ground, selected, designated, and alerted. The symbols depicted are examples . The line width, physical size, and hue of the figures are not requirements. The requirements are stated in the associated text.
a. Basic Directional (see Figure B-1).
(1) If directionality is valid, the basic directional traffic symbol must be depicted with an arrowhead shape oriented by the directionality.
(2) The color must be cyan or white.
(3) The color must be the same color as the basic non-directional symbol.
(4) The color should not be the same color as the own-ship symbol.
(5) For displays that do not integrate aircraft surveillance applications system (ASA) with TCAS, the symbol may be filled or unfilled.
(6) For TCAS/ASA-integrated systems and ATAS implementations, the symbol must be unfilled.
Figure B-1. Basic Directional Symbol
b. Basic Non-Directional (see Figure B-2).
(1) If directionality is invalid, the basic non-directional traffic symbol must be depicted with a diamond shape.
(2) The color must be cyan or white.
(3) The color must be the same color as the basic directional symbol.
(4) The color should not be the same color as the own-ship symbol.
(5) For displays that do not integrate ASA with TCAS, the symbol may be filled or unfilled.
(6) For TCAS/ASA-integrated systems and ATAS implementations, the symbol must be unfilled.
Figure B-2. Basic Non-Directional Symbol
c. Traffic Directionality. If the traffic symbol indicates directionality, the directionality of the traffic symbol must be displayed relative to the display orientation.
Note: The traffic directionality in air is based on traffic ground track angle, and not necessarily traffic heading. This is important for monitoring traffic such as helicopters that can fly backwards and to account for winds.
d. Traffic Application Capability. The traffic symbol may provide an indicatio n of traffic application capability.
Note 1: Traffic information that does not meet the minimum requirements for enhanced visual acquisition (EVAcq) should not be sent to the CDTI display from ASSAP.
Note 2: ASSAP may provide TCAS-only data that does not support EVAcq. TCAS data will still be displayed.
e. Traffic On-Ground Status (see Figure B-3).
color.
(1) If traffic is on-ground, the basic traffic symbol must be modified by changing the
(2) The color may be brown/tan.
(3) The size of on-ground traffic symbols may be decreased for additional encoding, and/or to reduce clutter.
(4) The symbol may be filled or unfilled.
Note: Additionally, altitude information is removed from the data tag.
() (} 0 Figure B-3. Directional and Non- directional On-ground Traffic Symbols
f. Basic Ground Vehicle (See Figure B-4)
(1) The basic Ground Vehicle symbol must be depicted as a top-down wheeled rectangular shape.
(2) The color should be the same as that used for the basic Traffic On-Ground symbol. The color may be brown/tan.
(3) Ground Vehicle directionality may be indicated by adding a triangular shape to one end of the rectangle, and orienting the entire symbol by directionality. Figure 8 provides an example notional depiction.
(4) The symbol may be filled or unfilled.
Figure B-4. Basic Surface Vehicle Symbol
2. Alerts.
The following requirements, per TSO-C195b, apply generally to CDTI-displayed alerts based on both ASA and TCAS systems. Additional TCAS-specific alert symbol requirements are provided in Appendix B, section 3.
a. Traffic that triggers an alert must be indicated on the Traffic Display with a symbol variation. The following requirements only apply to the alerted traffic symbol:
(1) If traffic directionality is valid, directionality information must not be removed during alerts.
(2) The traffic symbol must change to amber/yellow for caution level alerts.
(3) The traffic symbol must change to red for warning level alerts.
(4) For traffic without valid directionality:
(a) If traffic has a caution level alert, the traffic symbol may be modified by changing the shape to a circle.
(b) If traffic has a warning level alert, the traffic symbol may be modified by changing the shape to a square.
(5) For traffic with valid directionality:
(a) If traffic has a caution level alert, the traffic symbol may be modified by changing the shape to a circle with a directional inlay.
(b) If traffic has a warning level alert, the traffic symbol may be modified by changing the shape to a square with a directional inlay.
Note: Caution and warning level alerts may use the same traffic symbols as TCAS traffic advisories and resolution advisories, respectively.
(See Appendix B section 3)
(6) For airborne applications, alerting traffic that lies outside the configured traffic display range should be positioned at the measured relative bearing, and at the configured display maximum range (i.e., edge of display), and with a symbol shape modification that indicates that the traffic is off-scale.
Note: A half-symbol at the display edge is one acceptable indication method.
b. Proximate Traffic (see Figure B-5).
(1) For TCAS/ASA integrated systems and systems with ATAS, the traffic symbol must indicate airborne TCAS proximate status.
(2) If proximate traffic is displayed, the basic traffic symbol must be displayed as filled. Figure B-5 provides example notional depictions.
Note: This requirement is to be consistent with TCAS symbol convention.
A • Figure B-5. Proximate Directional and Non- directional Proximate Traffic Symbols
c. Selected Traffic.
(1) Selected traffic is traffic that is selected by the flight crew. Traffic selection results in display of additional traffic information beyond what is presented in the minimum data tag, and may enable other functions (e.g., designating traffic).
(2) If traffic selection is implemented:
(a) There must be some means of distinguishing the selected traffic from other traffic on the traffic display.
(b) A border must not be used to indicate selected traffic.
Note 1: A border is a discernable line that surrounds an existing symbol. Border types include fixed-shape or conformal.
Note 2: Borders are reserved for depicting designated traffic (see Figure B-6).
(3) When traffic is selected, additional information on that traffic must be displayed in a data block or a data tag.
Note: Generally, selecting traffic will bring up the additional information in a data block, but a data tag can also be used for this purpose.
(4) There must be an indication of off-scale selected traffic.
Note: A Selected half-symbol at the display edge and appropriate bearing is one acceptable method of indication.
d. Designated Traffic (see Figure B-6).
(1) Designated traffic is traffic upon which a designated application is to be performed. For example, in visual separation on approach (VSA), the traffic to be followed may be displayed as “designated” so that the application and the flight crew both know the 30
specific traffic upon which to act.
(2) If traffic designation is implemented:
(a) There must be some means of distinguishing the designated traffic from other traffic.
(b) If traffic is designated, the basic traffic symbol should be modified by adding a shape-conforming border. Figure B-6 provides a notional example.
Figure B-6. Directional and Non-directional Designated Traffic Symbols
(c) There must be an indication of off-scale designated traffic.
Note: A half-symbol at the display edge and appropriate bearing is one acceptable method of indication.
(d) The loss of “designated” status (e.g., due to signal loss or invalid data) must be indicated to the flight crew.
3. TCAS Alert Symbology for TCAS/ASA-Integrated Systems.
a. If traffic directionality is valid, directionality information must not be removed during a TCAS traffic advisory or resolution advisory.
Note: Directionality information, if available, may assist the flight crew in visual search and identification of the alerted traffic.
b. Traffic Advisories (see Figure B-7).
(1) If traffic has a TA, the traffic symbol must be modified by changing the color to amber/yellow, and changing the shape to a circle.
(2) Traffic with valid directionality must include a directional inlay.
(3) The size of TA traffic symbols may be increased to accommodate the shape modification.
(4) Line widths and fill may be changed to improve color interpretation and saliency.
ma Figure B-7. Traffic Advisory Symbols
c. Resolution Advisories (RAs) (see Figure B-8).
(1) If traffic has an RA, the traffic symbol must be modified by changing the color to red, and changing the shape to a square.
(2) Traffic with valid directionality must include a directional inlay.
(3) The size of RA traffic symbols may be increased to accommodate the shape modification.
(4) Line widths and fill may be changed to improve color interpretation and saliency.
Note: TCAS aural alerts and resolution guidance are not affected by these requirements or recommendations.
Figure B-8. Resolution Advisory S ymbols 32
ModeA/C Modes Aircraft Aural lnhibit(s)
e.g. TAWS ADS-B In ADS R TISB ModeA/C Modes ADS-8 In ADSR TIS B Aircraft Aural lnhibit(s)
e.g. TAWS I RF Source Aural Inhibit Audio Out Annunciator Panel Out t--- --------1 -<' L--- Annunciator Panel (TAS RA Display Out t---- Class B only) Traffic Display Out Notes: 1. Traffic Display Optional for TCAS 1/ TAS.
TAS/TCAS 1/TCAS 11 RA Display (TCAS II only) Aural Inhibit TAS/TCAS 1/TCAS II Track In I RF Source RF Source Audio Out t--------1 CDTI/Annunciator >----~ ATAS Audio Out Display Out TCAS I
- or TCAS 11
- or - Panel Out Audio Out TCAS Track In Display Out ATAS TAS Class A or B CDTI legacy Traffic Display (Note 1)
- or - Annunciator Panel Notes : 1. Annunciate the aura ls for TCAS as ATAS aurals i.e. for a TCAS only alert, issue the corresponding ATAS aural alert.
Speaker
2. TCAS II aurals are triggered from the TCAS traffic file.
Aural Inhibit L__--------- CDTI Integrated Unit 05/20/15 AC 20-172B Appendix C ATAS Integration with existing Traffic Alerting Avionics Figure C-1. Example of an acceptable configuration of TAS/TCAS I/TCAS II and ATAS Figure C-2. Example of an acceptable integrated configuration 33
ModeA/C Modes ADS-B In ADSR TIS B Traffic Display I RF Out Source Audio Out [TCAS I w/ or w/o Display]
- or - [TCAS II]
- or - [TAS Class A]
- or - -----------r ------ I I I An I I
- I I I I I CJ LegacyTCA Display nunciator Panel s [TAS Class B w/ or w/o Display] Spea ker Audio Out RF Annunciator Source Panel Out ATAS I ---- - 1----- .,e I I Annunc I -0---i 1ator -=- I I I I I I I Pan el : ______ D ADS-B Traffic Display Notes: Not permitted due to non-integration.
05/20/15 AC 20-172B Figure C-3. Example of an invalid TCAS I/TAS with ATAS configuration 34
Appendix D Definitions, acronyms, and related documents
1. Definitions. The following are definitions of terms used in this document.
24-bit Address. Unique address assigned to an aircraft during the registration process.
ADS-B In- Receipt, processing, and display of other aircraft’s ADS-B transmissions.
ADS-B In is necessary to utilize airborne applications.
ADS-B Out. Transmission of an aircraft’s position, altitude, velocity, and other
information to other aircraft and ATC ground based surveillance systems.
Advisory. The level or category of alert for conditions that require flight crew awareness and may require subsequent flight crew response.
Aircraft Surveillance Applications System (ASAS). An aircraft system based on airborne surveillance that provides assistance to the flight crew in operating their aircraft relative to other aircraft.
Airborne Surveillance and Separation Assurance Processing (ASSAP). The processing subsystem that accepts surveillance inputs (e.g., ADS-B reports), performs surveillance processing to provide reports and tracks, and performs application-specific processing.
Surveillance reports, tracks, and any application-specific alerts or guidance are output by ASSAP to the CDTI function. ASSAP surveillance processing consists of track processing and correlation of ADS-B, TIS-B, ADS-R and TCAS reports.
Alert. A general term that applies to all advisories, cautions, and warning information; can include visual, aural, tactile, or other attention-getting methods.
Application. The function(s) for which the ASA system is used.
Aircraft Surveillance Application (ASA). An application that uses aircraft surveillance data to provide benefits to the flight crew (refer to Table 1).
Antenna Offset Parameter. The distance from the nose of the aircraft to the GPS antenna.
For large aircraft, this offset is important in accurately placing the aircraft symbol on the airport map.
Automatic Dependent Surveillance-Broadcast (ADS-B). A function on an aircraft or surface vehicle operating within the surface movement area that periodically broadcasts its state vector (horizontal and vertical position, horizontal and vertical velocity) and other information. ADS-B is automatic because no external stimulus is required to elicit a transmission. It is dependent because it relies on on-board navigation sources and on-board broadcast transmission systems to provide surveillance information to other users.
Automatic Dependent Surveillance-Rebroadcast (ADS-R). A service of the ground system that rebroadcasts ADS-B messages from one link technology onto another. For 35