Appendix 2 FIGURE 2. IN-TRAIL PROCEDURE DISTANCES ILLUSTRATED
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, the closing Mach differential, as well as accuracy and integrity of the ADS-B data transmitted from participating aircraft. (See Table 1, In-Trail Procedure Initiation/Maneuver Criteria (reference RTCA DO-312).) The procedure further requires that the ITP aircraft maintain constant Mach, and climb or descend at a minimum of 300 feet per minute
Appendix 2 (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. ITP Distance and Groundsp eed 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 ground speed differential, the distance between the aircraft should not become less than the ITP minimum separation of 10 NM.
c. Relative Altitude Criteria. The reference aircraft may not be more than 2,000 feet above or below the ITP aircraft.
d. Similar Track Criteria. The ITP aircraft and any reference aircraft must be on similar tracks. Similar tracks are defined here as less than 45 degrees from one another. (See Figure 3, Similar Track).
e. Mach Differential. In order to ensure an acceptable closure throughout the ITP maneuver, the controller may 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:
• Using the cruise Mach numbers of the ITP and reference aircraft where the Mach number technique is being used;
• Requesting Mach numbers from the ITP and reference aircraft; or
• Any other methodology determined appropriate and acceptable by the regulatory authority and the Air Navigation Service Provider (ANSP).
f. ADS-B Data Quality Criteria. Only ADS-B OUT aircraft, broadcasting data of sufficient quality may be used as reference aircraft for ITP. Own ship data quality must also be sufficient to ensure safe separation. The data quality criteria are:
• Position accuracy for ITP and reference aircraft—ITP and reference aircraft data with horizontal position accuracies of at least 0.5 NM (95 percent).
• Position integrity for ITP and reference aircraft—ITP and reference aircraft data with horizontal position integrity bounds of 1.0 NM @ 1x10E 05.
• 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 knots) 95 percent.
Appendix 2 FIGURE 3. SIMILAR TRACK
5. ITP DESCRIPTION. To properly conduct an ITP, a qualified flightcrew must use 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 will 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. 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 will indicate to the flightcrew whether all initiation criteria are satisfied.
b. Flightcrew Requests ITP. If the criteria are satisfied, the flightcrew requests the ITP clearance using the appropriate phraseology. Direct Controller Pilot Communications (DCPC) is required; however, only Controller-Pilot Data Link Communication (CPDLC) is being used in locations where ITP are approved. Preformatted messages for requesting and approving ITP have not yet been developed, and flightcrews must use free text messages as described in Table 2, Flightcrew Free Text Controller-Pilot Data Link Communication Message Set for In-Trail Procedure, and Table 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 to allow the controller to properly evaluate the request.
NOTE: ATC must not issue an ITP clearance to any aircraft unless that aircraft has initiated the request.
c. 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.
Appendix 2
(b) Same Track includes the concept of Similar Track (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.
(3) Ensures both the ITP aircraft and reference aircraft are not maneuvering and not expected to maneuver during the ITP.
(a) 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.
d. 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 must immediately reject the ATC clearance and terminate the maneuver. Additionally, if the FL, reference aircraft, or type of maneuver (ITP versus standard FL change) does not match their request, or if the flightcrew receives an ITP clearance without requesting one, they must not perform the maneuver and should verify with ATC to confirm the clearance.
e. 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 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 must be completed.
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 300 fpm minimum vertical speed. Upon completion of the maneuver, notify ATC of the ITP data loss.
g. Approved ITP Variations. An ITP can be conducted with a maximum of two reference aircraft. The reference aircraft may not be more than 2,000 feet of altitude above or below the ITP aircraft, but there is no limit on the amount of altitude change the ITP aircraft may request.
The reference aircraft both may be behind or ahead of the ITP aircraft or one may be ahead and
Appendix 2 one behind. Figure 4, In-Trail Procedure Climb/Descent Variations, depicts the approved ITP variations.
h. Contingency Procedures. The ITP maneuver has been extensively tested both in flight and in computer simulations with consideration given to a variety of environmental and aircraft performance factors. A temporary breach of the 10 NM ITP distance does not constitute an inherently unsafe procedure and should not be the sole factor when considering abandoning the procedure. No new contingency procedures are prescribed for ITP. If, in the pilot’s judgment, the ITP maneuver (i.e., reaching the newly assigned altitude) cannot be successfully completed once the climb or descent has been initiated, he/she shall:
(1) Contact ATC and request an alternative clearance, as soon as practicable given flightcrew workload and flight conditions.
(2) Inform ATC of any action the flightcrew is taking or requesting. Because of the many variables, the CPDLC message should be in the “free text” format.
(3) Comply with regional contingency procedures appropriate to the circumstances, or as listed in International Civil Aviation Organization (ICAO) document PANS-ATM, DOC 4444, Section 15.2, Special Procedures for In-Flight Contingencies in Oceanic Airspace.
FIGURE 4. IN-TRAIL PROCEDURE CLIMB/DESCENT VARIATIONS
6. AUTHORIZATION TO CONDUCT ITP. Authorization from the FAA is required to conduct ITP. To receive authorization, operators should submit ITP proposals to their appropriate certificate management office (CMO), certificate-holding district office (CHDO), or Flight Standards District Office (FSDO) using the guidance contained in this section. ITP
Appendix 2 proposals must be evaluated and approved by the applicable FAA Flight Standards Service (AFS) policy divisions in Washington, DC, prior to authorization.
NOTE: Operators holding an active authorization for other ADS-B IN applications with specific requirements duplicated by those for ITP may reference such authorization requirements in their proposal as a means to demonstrate compliance with applicable ITP requirements.
a. Request for Authorization.
(1) Request for Authorization. U.S. operators seeking to conduct ITP must first contact their assigned FAA office to indicate their intent. When making an initial request, the operator should be prepared to provide the following:
(a) General information (aircraft, equipment, region of operation, etc.) about the proposed plan to conduct operations under the authorization; and
(b) The identification of the appropriate point(s) of contact (POC) for coordination during the FAA authorization process.
(2) At the time of the operator’s initial request, the FAA will provide the operator with information for obtaining relevant guidance and documents, as well as the proper content and format of the documentation required when submitting the formal request.
b. Required Documentation for Subm ission of Formal Proposal.
(1) Documentation Guidance. The following section provides general guidance on the documentation required for submission of a formal ITP proposal. At the discretion of the operator’s assigned principal inspector (PI), additional information may be required based on any unique aspects of their specific operation.
(2) Proposal Requirements. A separate proposal should be submitted for each aircraft type when making initial and subsequent requests for authorization to conduct ITP. Subsequent requests to add additional aircraft of the same make, model, and series (M/M/S) to an existing authorization should include the aircraft and equipment documentation required in paragraphs 4, 5, and 6 of this appendix.
(3) Letter of Request for Issuance of Authorization. The operator must submit a letter of request to the assigned PI requesting issuance of the authorization. The letter of request should include statements indicating the following:
(a) Proposed region(s) of operation;
(b) Type of aircraft M/M/S to be used;
(c) Description of ADS-B OUT/IN equipment to be used;
Appendix 2
(d) Revision of aircraft documents (Airplane Flight Manual (AFM), pilot’s operating handbook (POH), etc.);
(e) Establishment of applicable operational procedures and practices;
(f) Revision of applicable operations manuals and checklists;
(g) Revision of ADS-B IN system maintenance procedures;
(h) Revision of minimum equipment list (MEL), if applicable;
(i) Revision of pilot training; and
(j) Revision of dispatcher training (if applicable) or other persons with operational control.
(4) Aircraft Qualification. To conduct ITP, aircraft must have an ADS-B IN system that meets the standards of the current edition of Technical Standard Order (TSO)-C195a, Avionics Supporting Automatic Dependent Surveillance-Broadcast (ADS-B) Aircraft Surveillance Applications (ASA). For guidance on the installation of ITP equipment, refer to the current edition of Advisory Circular (AC) 20-165, Airworthiness Approval of Automatic Dependent Surveillance-Broadcast (ADS-B) OUT Systems, and AC 20-172, Airworthiness Approval for ADS-B IN Systems and Applications.
(5) Aircraft Equipment. Submit a description of the ITP equipment configuration to indicate the type of display (e.g., integrated with an existing display or hosted on a standalone display), location of the controls, and specifically include:
(a) ITP aircraft M/M/S;
(b) ITP aircraft registration numbers; and
(c) ITP equipment configuration data including:
• Surveillance processor Part Number (P/N).
• Transponder/ADS-B system P/N.
• ITP display P/N.
(6) Airworthiness. Submit instructions for continued airworthiness and return to service (RTS) maintenance procedures applicable to the ADS-B IN and ITP system equipment and software.
(7) Flight Manual/POH Documentation. Include relevant sections of the AFM, Aircraft Flight Manual Supplement (AFMS), or POH, which describe the ITP specific:
(a) System description;
(b) Cockpit setup procedures;
Appendix 2
(c) En route procedures;
(d) Communications; and
(e) Non-normal, contingency, and emergency procedures.
(8) Proposed ITP Operations Area. Authorizations to conduct ITP will be limited to specific regions of the world where the ANSP offers ITP and those procedures are determined to be acceptable to the Administrator. Include in your request a description, by flight information region (FIR) and ANSP, of the operational areas where you propose to conduct ITP. If you hold a B050 authorization, submit a draft B050 paragraph which includes the operational areas where you propose to conduct ITP, including applicable notes.
(9) Dispatch/Flight Planning. Submit applicable portions of proposed ITP-specific dispatch/flight planning training material to include any appropriate updates to the dispatch operations manual, or equivalent, as well as a description of the methods used to conduct, evaluate, and manage training.
(a) Recommended ITP Training Content. The following contains the recommended information to be included in dispatch/flight planning training material:
• General understanding of ADS-B IN operations;
• Route requirements;
• Equipment requirements; and
• Procedures for entry of applicable ADS-B equipment codes on flight plan.
(10) Pilot Training. Submit applicable portions of proposed ITP-specific pilot training material and include a description of the methods used to conduct, evaluate, and manage the training.
(a) Recommended ITP Training Content. The following contains the recommended information to be included in pilot training material:
• General understanding of ADS-B IN operations (technology, capabilities, and limitations).
• ITP system operation, including:
• Normal procedures.
• Abnormal, contingency, and emergency procedures.
• ITP flight planning considerations.
• ITP dispatch considerations (as applicable).
• MEL considerations (as applicable).
• ITP terminology, including proper formulation of an CPDLC ITP request/clearance.
• ITP equipment limitations.
Appendix 2
• Explanation of ITP distance as distinct from aircraft range, using select scenario-based examples (refer to Figure 2 for ITP distance geometries).
• ITP directly in trail of a reference aircraft.
• ITP aircraft on a crossing track of reference aircraft—diverging.
• ITP aircraft on a crossing track of reference aircraft—converging.
• ITP aircraft on a parallel track of reference aircraft.
(11) ITP Distance. Except when one aircraft is directly in trail of another, the ITP distance is not the same as the direct line distance between those two aircraft. (Refer to paragraph 3, ITP Terminology, for the exact description, and Figure 2 for examples.) Since the ITP software will be designed to calculate and display ITP distance information, extensive training on the subject is not necessary. However, it is important to emphasize that range and ITP distance are different. Consequently, a lack of understanding could lead the flightcrew to misidentify the correct reference aircraft(s) when requesting an ITP clearance. Training should include examples of the various ITP distance geometries depicted in Figure 2.
(a) Lateral Traffic Filters. Some ITP avionics may incorporate a lateral traffic filter.
The function of the traffic filter is to eliminate any targets beyond a predetermined lateral distance of own ship’s track from consideration as a potential reference aircraft. This is intended to prevent the flightcrew from misidentifying incorrect reference aircraft during their ITP request. The filter is most useful when in an organized track environment, or where traffic may be on a parallel user-preferred route. Training should include recommended technique for its use.
(b) ITP Initiation Criteria. Traffic displayed as an ADS-B IN target may not be made available as a valid ITP reference aircraft because it does not meet one or more ITP initiation criteria. Some of the criteria, such as position accuracy, are not displayed to the flightcrew. Training should include a discussion of the initiation criteria, which criteria are known to the flightcrew, and examples of when a displayed ADS-B IN target is not an eligible ITP reference aircraft. Refer to Table 1 for ITP initiation criteria.
Appendix 2 TABLE 1. IN-TRAIL PROCEDURE INITIATION/MANEUVER CRITERIA (REFERENCE RTCA DO 312) In-Trail Procedure (ITP) Speed/Distance Criteria ITP Distance >= 15 nautical miles (NM) and Closing Ground Speed Differential <= 20 knots ITP Distance >= 20 NM and Closing Ground Speed Differential <= 30 knots Relative Altitude Criteria Difference in altitude between the ITP and Reference Aircraft is less than or equal to 2,000 feet Similar Track Criteria Difference in track angles between ITP and Reference Aircraft less than +/- 45 degrees Position Accuracy for ITP and Reference Aircraft ITP and Reference Aircraft data with horizontal position accuracies of at least 0.5 NM (95%) Position Integrity for ITP and Reference Aircraft ITP and Reference Aircraft data with horizontal position integrity bounds of 1.0 NM @ 1x10E-05 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 knots) 95% Closing Mach Differential (Air Traffic Control (ATC) Crosscheck) Closing Mach Differential equal or less than
0.06 Mach
Appendix 2 TABLE 2. FLIGHTCREW FREE TEXT CONTROLLER-PILOT DATA LINK
COMMUNICATION MESSAGE SET FOR IN-TRAIL PROCEDURE In-Trail Procedure (ITP) type (number and relative position of reference aircraft) FREE TEXT Message Element Content 1 reference aircraft (ahead) “ITP [D istance] BEHIND [Aircraft flight identification]” 1 reference aircraft (behind) “ITP [D istance] AHEAD OF [Aircraft flight identification]” 2 reference aircraft (both ahead) “ITP [Distance] BEHIND[Aircraft flight identification] AND [Distance] BEHIND [Aircraft flight identification]” 2 reference aircraft (both behind) “ITP [Distance] AHEAD OF [Aircraft flight identification] AND [Distance] AHEAD OF [Aircraft flight identification]” 2 reference aircraft (one ahead and one behind) “ITP [Distance] BEHIND [Aircraft flight identification] AND [Distance] AHEAD OF [Aircraft flight identification]”
To request an ITP climb or descent, the flightcrew will send a CPDLC REQUEST CLIMB TO [altitude] or REQUEST DESCENT TO [altitude]) message, as applicable, with the following verbiage added to FREE TEXT as listed in Table 2.
Example of ITP request message: REQUEST CLIMB TO FL360 ITP 25NM BEHIND SIA228 AND 21NM AHEAD OF AFR008.
NOTE: This preformatted free text message set will be used until an appropriate message set is implemented.
Appendix 2 TABLE 3. CONTROLLER FREE TEXT CONTROLLER-PILOT DATA LINK
COMMUNICATION MESSAGE SET FOR IN-TRAIL PROCEDURE In-Trail Procedure (ITP) type (number and relative position of reference aircraft) FREE TEXT Message Element Content 1 reference aircraft (ahead) “ITP BE HIND [Aircraft flight identification]” 1 reference aircraft (behind) “ITP AHEAD OF [Aircraft flight identification]” 2 reference aircraft (both ahead) “ITP BE HIND [Aircraft flight identification] AND BEHIND [Aircraft flight identification]” 2 reference aircraft (both behind) “ITP AHE AD OF [Aircraft flight identification] AND AHEAD OF [Aircraft flight identification]” 2 reference aircraft (one ahead and one behind) “ITP BEHIND [Aircraft flight identification] AND AHEAD OF [Aircraft flight identification]” To grant an ITP request, the controller will send an uplink message containing CLIMB TO AND MAINTAIN [altitude] or DESCEND TO AND MAINTAIN [altitude] containing the text in Table 3:
Example of ITP clearance message: ITP BEHIND SIA228 AND AHEAD OF AFR008 CLIMB TO FL360 REPORT LEVEL FL360.
NOTE: The controller should never issue an ITP clearance unless one has been requested by a flightcrew.
NOTE: This preformatted free text message set will be used until an appropriate message set is implemented.