4-13 Navigation Equipment Using the Global Positioning System Augmented by the Satellite Based Augmentation System (SBAS), are SBAS receivers.
4.5.1.5 Aircraft-Based Augmentation System (ABAS) sensors tightly integrate GPS measurements with inertial reference/navigation sensor data, improving the quality and robustness of positioning performance. This difference in performance is most pronounced for lower level Required Navigation Performance (RNP) operations, such as Area Navigation (RNAV) approaches, and for all operations when there are inoperative GPS satellites.
Note 1: Some GPS receivers manufactured with a TSO-C129a approval are SA-Aware, and, therefore, have the same NACp and NIC availability as TSO-C196( )-approved equipment. Operators should check with their GPS receiver supplier to verify whether their installed TSO-C129( ) GPS receiver is SA-On or SA-Aware.
Note 2: The Wide Area Augmentation System (WAAS) is the designation of the SBAS available in North America and is the term often used when making reference to SBAS in the United States.
4.5.2 GPS Performance Prediction. For aircraft equipped with TSO-C129( ) GPS units to support ADS-B Out equipment, an NACp and NIC GPS service availability prediction should be performed for the intended route of flight (route and time) using available GPS satellite information and guidance published in this AC. It is not necessary for operators of aircraft equipped with the following receivers to conduct a preflight availability prediction: WAAS (TSO-C145 or TSO-C146), SA-Aware (TSO-C196), TSO-C129a receivers that are SA-Aware, or ABAS that include SA-Aware GPS receivers.
4.5.2.1 Prediction Methods. Operators may use any of the following preflight availability prediction methods.
4.5.2.1.1 Operators of large fleets of aircraft or users of flight planning programs may wish to use their own preflight availability verification tool. The operator is responsible for selecting a tool that accurately predicts the ADS-B position source performance for their aircraft. The tool needs to account for the GPS satellites that are in service at the time of the prediction, and may take into account unique characteristics of the GNSS receiver, aircraft integration, or installation, including performance better than required in FAA standards or use of inertial information integrated into the ADS-B Out position source. The FAA does not evaluate or approve a particular tool, but may evaluate the basis of the operator’s determination that the tool is appropriate to their aircraft, particularly if its use results in noncompliant flights in airspace where ADS-B Out is required.
4.5.2.1.2 Operators may use the FAA-provided preflight availability prediction tool, called the Service Availability Prediction Tool (SAPT) (https://sapt.faa.gov).
Refer to the SAPT User Guide for specific instructions on its use.
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4.5.2.1.3 Operators may use a third-party interface, incorporating FAA GPS performance prediction data without altering performance values, to predict NACp/NIC performance outages for the aircraft’s predicted flightpath and times.
4.5.2.2 Prediction Model Parameters. The operator should use a model appropriate to their equipment, including the type of GPS receiver and the demonstrated capability to track satellites at a given mask angle. When selecting a mask angle, the operator should consider the equipment qualification, installation in the aircraft, and the effects of normal maneuvering. Aircraft are typically qualified with a 5-degree mask angle, and operational experience has indicated that a 2-degree mask angle can be achieved by some equipment installations. If using the SAPT, each prediction is valid for the operation within 5 minutes of the plan time and 7.5 nautical miles (NM) of the route.
The operator may wish to submit additional requests for predictions for varying times around the proposed departure time to ensure compliance at the actual departure time.
4.5.2.3 Flight Planning Guidance. Predictions should be conducted within 24 hours of departure and as close to departure time as feasible, but with sufficient time to replan the flight in the event a segment along the planned route is predicted to have insufficient GPS service availability. The prediction should be reevaluated prior to flight if new information (i.e., a Notice to Air Missions (NOTAM)) provides notice of an unscheduled GPS satellite outage. In the event of a predicted loss of performance for any part along the intended route in the airspace where ADS-B Out is required, the flight should be replanned so that ADS-B Out performance requirements specified in 14 CFR § 91.227 can be met.
4.5.3 Preflight Prediction Compliance. Operators need to perform an ADS-B Out preflight prediction only for the intended route of flight to the intended destination. For example, when departure and/or arrival alternate airports are required, no preflight prediction is necessary for these routes. However, if you become aware of a change that could result in degraded ADS-B Out performance, such as a satellite outage prior to receiving an ATC clearance for the intended route of flight, then you should conduct a subsequent preflight prediction for the planned flight. This will ensure that ADS-B Out performance is still predicted to comply with the performance requirements of 14 CFR § 91.227(c)(1)(i) and (iii). Once the pilot has received an ATC route clearance, there is no requirement to conduct a subsequent preflight prediction. Therefore, upon receiving a satisfactory preflight availability prediction and an ATC clearance for an intended route of flight, the operator will be deemed to have complied with the preflight availability prediction requirement and the performance requirements of 14 CFR § 91.227(c)(1)(i) and (iii). The FAA accepts that unanticipated changes in route of flight and environmental conditions may adversely affect ADS-B Out performance. ATC will continue to exercise its responsibility for the safe and efficient movement of air traffic, including the routing of traffic to meet those objectives. ADS-B preflight planning should include:
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• Identification of flights or aircraft that require completion of a preflight prediction.
• Identification of the preflight prediction system (or systems) to be used.
• A means to document completion of a satisfactory prediction for each flight where a prediction is required.
• Retention of prediction completion documentation for a suitable period of time, such as 3 months.
4.5.4 GPS Interference With ADS-B Compliance. There may be times when the GPS position source cannot meet the required technical performance for compliance with 14 CFR § 91.227 due to planned GPS interference. In the event of a scheduled interference outage of GPS, the FAA will issue a NOTAM that identifies the airspace and time periods that may be affected by the interference. The FAA has determined that it would be impractical and not in the public interest to require operators to avoid the affected area based on the chance that an otherwise compliant flight could experience GPS interference. Accordingly, operators should proceed with their intended operation if the only impediment to their operation is possible planned GPS interference. An operator who is required to perform a preflight availability prediction for the intended route of flight is still required to obtain a satisfactory preflight availability prediction. When a NOTAM identifies the airspace and time periods that may be affected by GPS interference, an operator will not be required to alter their route of flight to avoid the area based solely on that NOTAM. If an operator encounters actual GPS interference during their flight that results in a degradation of ADS-B Out performance, provided the operator has taken the appropriate preflight actions, the FAA will not consider these events to constitute a violation, as such application of the regulation would impose standard of conduct wholly outside the operator’s control.
4.5.5 SAPT Outages. The FAA will issue a NOTAM in the event of a SAPT outage. Operators who use SAPT as their preflight prediction tool will not need to conduct a preflight prediction for the duration of the outage. Additionally, any FPs submitted to ATC with a proposed departure time within 90 minutes of SAPT return to service do not require a subsequent preflight analysis. When there is a SAPT outage and an operation falls below the performance requirements, provided the operator has taken the appropriate preflight actions with regard to relying upon SAPT, the FAA will not consider these events to constitute a violation, as such application of the regulation would impose standard of conduct wholly outside the operator’s control. For operators who have been notified by the FAA of consistent and repeated ADS-B Out performance issues, the FAA cautions that operating during a SAPT outage without first redressing the identified nonperformance issue will be considered a continuation of existing noncompliance of the performance requirements.
4.6 Flightcrew Entry of Required ADS-B Data. The operator should develop operational procedures to address flightcrew entry of the ADS-B message elements required in 14 CFR § 91.227 and as described in paragraphs 4.6.1 through 4.6.4. If the ADS-B avionics system design does not allow for a single point of entry for this information, the AFM, AFMS, RFM, RFMS, POH, or other required flight manual must address the
4-16 requirement to enter the information multiple times through the appropriate system’s interface and to ensure that conflicting ACID information is not transmitted to ATC.
4.6.1 Mode A Code.
4.6.1.1 ATC automation relies on the Mode A code to identify aircraft under radar surveillance and to correlate the displayed target to an FP. The Mode A code is one element of the transmitted ADS-B message set. Since SSR and ADS-B surveillance will overlap in much of the NAS, correlation of the Mode A code between the transponder and the ADS-B message is necessary to ensure that a single target is resolved and correlated to an FP route.
4.6.1.2 It is imperative that the ATC-assigned transponder code is identical to the one in the ADS-B Out message. Refer to AC 20-165 for more information.
Note: Transmission of conflicting transponder and ADS-B Mode A codes will result in erroneous traffic conflict alerts within the ATC automation system.
4.6.2 Aircraft’s FLT ID.
4.6.2.1 An aircraft’s FLT ID is transmitted by the ADS-B Out avionics. Per 14 CFR § 91.227(d)(8), the FLT ID must be identical to the “Aircraft Identification” as entered in Item 7 of FAA Form 7233-4 and Item 2 of FAA Form 7233-1, Flight Plan, which limit it to a maximum of seven alphanumeric characters. It is also referred to as a call sign. The FLT ID is typically entered by the flightcrew during preflight through either a flight management system (FMS) interface (control display unit (CDU)) or transponder control panel. The FLT ID for General Aviation (GA) aircraft is typically the aircraft’s registration number. The aircraft owner can preset the FLT ID to the aircraft’s registration number (e.g., N235RA), since it is a fixed value, or the pilot can enter it into the ADS-B Out system prior to flight, provided the ADS-B avionics have this capability. It is important to know that the FLT ID should be input into the ADS-B system exactly as filed in Item 2 of FAA Form 7233-1 or Item 7 of FAA Form 7233-4. No additional characters should be used to fill all available fields.
4.6.2.2 Some ATC systems use transmitted FLT IDs to uniquely identify each aircraft within a given airspace and correlate them with a filed FP for the provision of surveillance and separation services. If the FLT ID is not entered correctly, ATC automation systems may not associate surveillance tracks for the aircraft to its filed FP. Therefore, air traffic services may be delayed or unavailable until this is corrected. Consequently, it is imperative that flightcrews and GA pilots ensure the FLT ID entry correctly matches the ACID annotated in the filed ATC FP prior to departure.
4.6.2.3 In FAA ATC systems, if the FLT ID transmitted by the aircraft’s ADS-B system does not exactly match the FLT ID on the FP, a call sign mismatch
4-17 (CSMM) occurs. When a CSMM occurs and the ATC functionality is enabled, the controller is alerted and may take action, resulting in a flight delay. Furthermore, ATC may elect to advise the Flight Standards Service (FS) of the event and the potential violation of 14 CFR § 91.227(d)(8). The specific wording of this regulation has caused misunderstanding from numerous operators and airmen who believe it is acceptable to have a different FLT ID on the FP [ABC1234] from the FLT ID [N12345] transmitted by ADS-B. In an August 3, 2017, legal interpretation, the FAA Office of the Chief Counsel found that the intent of 14 CFR § 91.227(d)(8) is to require that the FLT ID as entered on the FP must exactly match the ADS-B-transmitted FLT ID. See Table 4-1, Aircraft Identification Transmission Examples, for examples.
Table 4-1. Aircraft Identification Transmission Examples Flight Plan Aircraft ID Correct ADS-B Transmission Incorrect ADS-B Transmission AAL5688 AAL5688 AAL-5688 SWA2155 SWA2155 2155 UAL21 UAL21 UAL0021 DAL9450 DAL9450 N561DL ASH5861 ASH5861 ASH5872 N350QS N350QS EJA350 FDY1055 FDY1055 VFR N777JK N777JK N-777JK N123DJ N123DJ NGF123
CGABC CGABC C-GABC
VHXYZ VHXYZ VH-XYZ N100PH N100PH N1OOPH
4.6.2.4 GA pilots occasionally have the opportunity to use an FLT ID provided by a charity or other organization instead of using their N-number. In this situation, the GA pilot may only use the organization’s FLT ID for the flight, provided they change the FLT ID transmitted by the ADS-B Out avionics. If the ADS-B equipment does not allow the FLT ID to be changed or the pilot is unsure of how it is accomplished, the pilot should not use the organization’s FLT ID. In this case, in order to ensure compliance with 14 CFR § 91.227(d)(8), the pilot should use the aircraft registration number as the FLT ID.
4.6.2.5 Aircraft owners/operators are encouraged to periodically verify that their ADS-B is broadcasting the correct FLT ID. This is particularly true after any maintenance has been performed on the aircraft, even if not directly associated with avionics. The free FAA PAPR (described in paragraph 4.3.2.5.6) is an excellent tool to verify the output of ADS-B parameters, including FLT ID.
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4.6.3 Emergency Status.
4.6.3.1 This ADS-B message element and transponder code alerts ATC that the aircraft is experiencing emergency conditions and indicates the type of emergency. The appropriate Mode A code should be entered into the transponder (e.g., 7500, 7600, or 7700). The ICAO Annex 10, Aeronautical Telecommunications, Volume IV, Surveillance and Collision Avoidance Systems, emergency codes (general emergency, no communications, and unlawful interference) are required by 14 CFR § 91.227.
4.6.3.2 ADS-B systems integrated within a transponder will automatically set the applicable emergency status when code 7500, 7600, or 7700 is entered into the transponder. Transponders compliant with RTCA DO-181F, Minimum Operational Performance Standards for Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment, will also automatically set the applicable emergency status when code 7400 is entered into the transponder.
4.6.4 Transponder IDENT Function. The AFM or POH will provide specific instructions on how the IDENT feature will be activated in specific installations, including any installations with multiple IDENT features.
Appendix A A-1 APPENDIX A. ADS-B IN-TRAIL PROCEDURE A.1 Purpose. This appendix provides a description of the ADS-B-enabled In-Trail Procedure (ITP) and guidance to operators seeking FAA authorization to conduct ITP operations.
A.2 Background. The ITP is designed primarily for use in nonradar oceanic airspace to enable appropriately equipped ADS-B In aircraft to perform flight level (FL) changes previously unavailable with procedural separation minima applied. The improved traffic information available to ADS-B In-equipped aircraft allows ITP maneuvers to occur safely with reduced separation minima applied. ITP enables flightcrews to execute FL changes to improve ride comfort, avoid weather, or obtain more favorable winds to improve fuel economy and arrival times.
A.2.1 ITP Scenario. Figure A-1, Reduction of Aircraft Separation Minima With In-Trail Procedure, illustrates a basic ITP scenario. The ITP aircraft (blue) wishes to climb from FL340 to 360 between two reference aircraft (red) where procedural separation minima is applied. Using onboard ADS-B In and ITP equipment, the ITP aircraft can determine if the necessary criteria can be met and, if so, request air traffic control (ATC) approval to execute the desired FL change using reduced separation minima between the two reference aircraft.
A.2.2 ATC Responsibility. ATC maintains separation responsibility throughout the ITP maneuver, and resumes the appropriate separation minima at its completion. ATC will apply the reduced ITP separation only between a qualified ITP aircraft and no more than two reference aircraft for the duration of the maneuver. The ITP maneuver can be performed with reference aircraft that do not have ADS-B In equipment. To enable an ITP maneuver, it is necessary for the reference aircraft to transmit an ADS-B Out signal of sufficient quality.
Figure A-1. Reduction of Aircraft Separation Minima With In-Trail Procedure A.
3 ITP Terminology.
A.3.1 Closing Groundspeed (GS) Differential. The difference between the ITP aircraft’s GS and a reference aircraft’s GS that results in a reduction of the ITP distance.
Appendix A A-2 A.3.2 Closing Mach Speed Differential. The difference in Mach speed between the ITP aircraft and the reference aircraft that results in a reduction of the ITP distance.
A.3.3 ITP Aircraft. An aircraft operated by a flightcrew authorized to conduct an ITP.
A.3.4 ITP Criteria. A set of conditions to be satisfied prior to initiating or executing an ITP clearance that ensures the safety of the procedure.
A.3.5 ITP Distance. The distance between the ITP aircraft and reference aircraft as defined by the difference in distance to an aircraft calculated common point along a projection of each aircraft’s track in front of or behind the aircraft, as appropriate. (See Figure A-2, In-Trail Procedure Distances Illustrated.) For the case where aircraft are on parallel tracks, the ITP distance is measured along the track of one of the aircraft using its calculated position and the point abeam the calculated position of the other aircraft. This measurement technique is similar to the method described in International Civil Aviation Organization (ICAO) Doc 4444, Procedures for Air Navigation Services—Air Traffic Management, Section 5.4.2.9, Performance-Based Longitudinal Separation Minima.
A.3.6 ITP Equipment. The onboard avionics that support an ITP.
A.3.7 Reference Aircraft. Aircraft (no more than two) transmitting valid ADS-B data that meet specified criteria and are referenced as part of an ITP clearance request to ATC.
Appendix A A-3 Figure A-2. In-Trail Procedure Distances Illustrated A.
4 ITP Concept. The ITP concept is based on the aircraft satisfying specific initial conditions and the flightcrew promptly and correctly executing the requested procedure once approved. The initial conditions are the ITP speed/distance criteria, the relative altitude criteria, the similar track criteria, and the closing Mach differential, as well as the accuracy and integrity of the ADS-B data transmitted from participating aircraft. (See Table A-1, In-Trail Procedure Initiation/Maneuver Criteria (Reference RTCA DO-312 Supplement).) The safety of the procedure depends upon the ITP aircraft maintaining
Appendix A A-4 constant Mach and climb or descend at a minimum of 300 feet per minute (fpm) during the maneuver. With these criteria, an ITP aircraft should never come closer than the 10-nautical-mile (NM) separation minimum to a reference aircraft while passing through their altitude(s).
A.4.1 ITP Distance and GS Differential Criteria. The initial distance criteria values, 15 NM and 20 NM, were selected so that when an FL change at 300 fpm and constant Mach number is maintained with the respective maximum 20- or 30-knot closing GS differential, the distance between the aircraft should not become less than the ITP minimum separation of 10 NM.
A.4.2 Relative Altitude Criteria. The design of the procedure is such that the reference aircraft may not be more than 2,000 feet above or below the ITP aircraft.
A.4.3 Similar Track Criteria. Application of the ITP is limited to geometries where the ITP aircraft and any reference aircraft are on similar tracks. Similar tracks are defined here as less than 45 degrees from one another. See Figure A-3.
Figure A-3. Similar Track A .4.4 Mach Differential. In order to ensure an acceptable closure throughout the ITP maneuver, the controller will not issue an ITP clearance if the closing Mach differential is greater than 0.06 Mach. This Mach differential check accounts for potentially unsafe closure rates due to abnormal or adverse wind gradient conditions at the intermediate altitudes.
The Mach number check may be achieved by:
1. Using the cruise Mach numbers of the ITP and reference aircraft where the Mach number technique is being used;
2. Requesting Mach numbers from the ITP and reference aircraft; or
3. Any other methodology determined appropriate and acceptable by the regulatory authority and the air navigation service provider (ANSP).
Appendix A A-5 A.4.5 ADS-B Data Quality Criteria. The ITP avionics only accept ADS-B Out aircraft broadcasting data of sufficient quality for use as reference aircraft for ITP. The ITP avionics only allow ITP when own-ship data quality is sufficient to ensure safe separation. The data quality criteria are:
1. Position accuracy for ITP and reference aircraft—ITP and reference aircraft data with horizontal position accuracies of at least 0.5 NM (95 percent);
2. Position integrity for ITP and reference aircraft—ITP and reference aircraft data with horizontal position integrity bounds of 1.0 NM at 1×10E-05; and
3. Velocity accuracy for ITP and reference aircraft—ITP and reference aircraft data with horizontal velocity accuracies of at least 10 meters/second (m/s) (19.4 kts), 95 percent.
A.5 ITP Description. To properly conduct an ITP, a qualified flightcrew uses ADS-B In avionics specifically certified to assist in verifying the initial conditions and a graphical display to monitor the relative position(s) of nearby aircraft. The procedure can only be conducted in airspace with appropriately trained ATC personnel, ITP-compatible automation, and approved ITP separation minima available. The following are the steps necessary to conduct an ITP:
A.5.1 Flightcrew Verifies Initial Criteria. Using approved avionics, the ITP flightcrew verifies that their own-ship and the reference aircraft meet initial qualifying criteria. The onboard ITP avionics indicate to the flightcrew whether all initiation criteria are satisfied.
A.5.2 Flightcrew Requests ITP. If the criteria are satisfied, the flightcrew requests the ITP clearance using the appropriate phraseology. Direct Controller Pilot Communication (DCPC) ensures unambiguous communication of the ITP request and ATC clearance.
Currently, only Controller-Pilot Data Link Communication (CPDLC) is being used in locations where ITP is approved. Preformatted messages for requesting and approving ITP have been developed; however, not all aircraft have implemented them. In aircraft that do not have preformatted messages, flightcrews use standardized free text messages as described in Table A-2, Flightcrew Standardized Free Text Controller-Pilot Data Link Communication Message Set for In-Trail Procedure, and Table A-3, Controller Free Text Controller-Pilot Data Link Communication Message Set for In-Trail Procedure, until further notice. It is essential that the correct message elements be included in the correct format to allow the controller or automation system to properly evaluate the request.
Improperly formatted or incomplete requests may be denied.
Note: ATC will not issue an ITP clearance to any aircraft unless that aircraft has initiated a proper request.
Appendix A A-6 A.5.3 Controller Issues Clearance. Upon receipt of an ITP request, the controller:
1. Confirms the ITP aircraft and the reference aircraft are on the same track.
a. Same-track criteria are not the same as the similar-track criteria, which are checked by the ITP aircraft flightcrew.
b. Same-track includes the concept of similar-track (i.e., ITP aircraft and reference aircraft are traveling in the same direction with less than a 45-degree relative track angle between the aircraft), but also includes a check on whether or not the lateral protection areas overlap (e.g., lateral separation cannot be applied). This check can only be done by the controller who knows what separation standard is being applied between the aircraft.
2. Confirms that no more than two reference aircraft have been identified in the request and are identified correctly; that is, that the Aircraft Identification (ACID) of each reference aircraft in the ITP request exactly matches the corresponding aircraft’s filed flight plan (FP).
3. Ensures both the ITP aircraft and reference aircraft are not maneuvering and not expected to maneuver during the ITP.
Note: A change of course (only) to remain on the same route would not be considered a maneuver, provided the course change is less than 45 degrees and the aircraft remain in a same track configuration.
4. Verifies that the closing Mach differential is no greater than 0.06 Mach.
5. Verifies that there are no conflicts at the requested altitude.
6. If appropriate, issues an ITP clearance.
A.5.4 Flightcrew Reassesses Criteria. Upon receiving the ITP clearance, the flightcrew confirms that all criteria are still satisfied. If the criteria are not satisfied or there has been a loss of traffic information, the flightcrew immediately rejects the ATC clearance and terminates the maneuver. Additionally, if the FL, reference aircraft, or type of maneuver (ITP versus standard FL change) does not exactly match their request or if the flightcrew receives an ITP clearance without requesting one, they will not perform the maneuver and should verify with ATC to confirm the clearance.
A.5.5 Flightcrew Executes ITP. If the criteria are still met, the flightcrew accepts the clearance and begins the requested climb or descent without delay. While executing the maneuver, the flightcrew is expected to maintain their flight-planned route, assigned Mach number (or current Mach, if none is assigned), and minimum Vertical Speed (VS) of 300 fpm and ensure they execute only the maneuver for which they have been cleared. The maneuver is complete once the flightcrew reports to ATC that they have reached the new FL.
Note: Once the ITP maneuver has been initiated, it should be completed, and the aircraft not returned to the initial altitude. Should reference aircraft data be lost or ITP display fail during the maneuver, the flightcrew should continue the maneuver to the assigned altitude using the appropriate Mach number and