Appendix F F-5 F.4.5 Flight Identification (FLT ID). The flight identification, or FLT ID, can be the telephonic “call sign” (e.g., “Brickyard 3691”), the International Civil Aviation Organization (ICAO) three-letter designator (3LD) combined with a flight number (e.g., “RPA3691”), or the registration number of the aircraft (e.g., “N12345”). The FLT ID of the lead aircraft is given by ATC in the IM clearance.
F.4.6 Interval Management (IM) Aircraft. An aircraft that is equipped with FIM avionics, flown by an IM-qualified flightcrew.
F.4.7 Interval Management (IM) Clearance Type. The basic action that ATC instructs IM aircraft flightcrew to perform as part of the IM operations. The IM clearance types are Achieve-by Then Maintain, Maintain Current Spacing, Capture Then Maintain, Final Approach Spacing, and IM Turn.
F.4.8 Interval Management (IM) Path Monitoring. An internal FIM avionics function that leads to the removal of IM information when either the IM aircraft or the lead aircraft vary from their expected route by a predetermined amount.
F.4.9 Interval Management (IM) Speed. The speed in IAS or Mach calculated by the FIM avionics that the flightcrew flies to conform to the ATC IM clearance and to achieve or maintain the ASG.
F.4.10 Interval Management (IM) Speed Compliance Monitoring. An internal FIM function designed to ensure precise flightcrew adherence to IM speed changes. The speed monitoring may include visual and aural alerting that notifies the flightcrew when the aircraft speed varies from the IM speed by a predetermined amount, or that the flightcrew has not responded to an IM speed change for a predetermined amount of time.
F.4.11 Planned Cancellation Point (PCP). A point on the IM aircraft’s planned flightpath where the IM operations end normally. Also referred to as the “Planned Termination Point” in industry standards.
F.4.12 Selected Traffic. Traffic uniquely chosen by the flightcrew via the CDTI to obtain additional information (e.g., FLT ID and GS). The FIM avionics will make selected traffic distinguishable from all other traffic on the traffic display. Selected traffic is not participating in an IM operation (but designated traffic is).
F.5 IM Clearance Types Described. The FIM avionics standard contains five clearance types: Maintain Current Spacing, Capture Then Maintain, Achieve-by Then Maintain, Final Approach Spacing, and IM Turn. These clearance types describe the functions the FIM avionics perform; however, the terms used over the voice frequency and that are shown on the flightcrew interface may change to align with approved phraseology. ATC does not currently plan to implement the IM Turn clearance type in the NAS, so we do not address it here. We will add information related to IM Turn to a future revision of this appendix should that change.
Appendix F F-6 F.5.1 Clearance Type Format. Each clearance type has required clearance elements and optional clearance elements for ATC to provide. For all clearance types, ATC will provide the FLT ID of the lead aircraft along with the clearance type. For all clearance types, there is an ASG; ATC will state the ASG (in units of time or distance), or it will be implied (i.e., current spacing). ATC will provide the IM aircraft the planned route for the lead aircraft and the CP for the Achieve-by Then Maintain clearance type. The PCP is optional for all clearance types, but the FIM avionics will default the PCP in close proximity to the destination airport if a PCP is not entered.
F.5.1.1 See Table F-1 for a summary of the acceptable clearance element formats.
The ASG will be expressed in time (seconds) or distance. ATC will provide the CP and PCP as navigational fixes. The lead aircraft planned route will be given as a Standard Terminal Arrival Route (STAR), airway or approach procedure, or as a combination of those procedure types.
Table F-1. Clearance Element Formats Clearance Element Format Examples Assigned spacing goal (ASG) Time or distance 90 seconds, 10 nautical miles (NM) Lead aircraft planned route Standard Terminal Arrival Route (STAR), airway, approach, waypoint, or sequence of waypoints EAGUL6, J186, ILS 36R Cross Point (CP) Navigation fix SLIDR, PINNG, 10 NM EAST OF SLIDR Planned Cancellation Point (PCP) Navigation fix EAGUL, DRRVR F.5.2 Maintain Current Spacing. ATC can issue a Maintain Current Spacing clearance expressed in either time or distance. For example, while an IM aircraft is transiting an en route sector, the controller seeing that the current spacing is suitable for delivery to the next sector gives the following: “TRAIL 456 Maintain current time behind LED123,” or “TRAIL 456 Maintain current distance behind LED123.”
Appendix F F-7 Figure F-1. Maintain Current Spacing F.5.3 Capture Then Maintain. ATC can issue a Capture Then Maintain clearance when the IM aircraft and the lead aircraft are on similar routes. The FIM avionics will provide IM speeds to move the IM aircraft to the ASG. A sample IM clearance could be:
“TRAIL 456 Capture then maintain 10NM behind LED123.”
Figure F-2. Capture Then Maintain F.5.4 Achieve-by Then Maintain (“Cross”). When ATC needs the ASG achieved by the time the IM aircraft reaches a particular fix, the controller may issue an Achieve-by Then Maintain clearance. The lead aircraft and IM aircraft may be on different paths at the time of the clearance, but will cross a common fix. The clearance will contain the lead aircraft’s planned route and the identification of the fix to cross, and optionally the PCP.
The ASG can be expressed in time or distance. An example could be: “TRAIL 456 Cross HONEE 90 seconds behind LED123 on the BRAVO Transition. Cancel at LASFX.” The IM flightcrew will fly the IM speeds to achieve the ASG by the time they cross the CP.
They will maintain the ASG until the PCP, or until the controller cancels the IM operation.
Appendix F F-8 Figure F-3. Achieve-by Then Maintain (Cross) F.5.5 Fi nal Approach Spacing. ATC may issue a Final Approach Spacing clearance when one or both of the lead aircraft and the IM aircraft will be on the same final approach course.
One aircraft can be on an intercept to final if the other aircraft is already established on the final approach course. The controller will include the lead Aircraft Identification (ACID) and the ASG.
Figure F-4. Final Approach Spacing F.5.6 IM Suspend. ATC may have a need to interrupt an active IM operation, such as to resolve a developing traffic conflict. IM Suspend is not strictly a clearance type. It is functionality in the FIM avionics that temporarily removes IM speeds, indications, and alerts, but retains the basic IM clearance information.
F.5.7 SafeRoute+ Differences. SafeRoute+ is the Aviation Communication & Surveillance Systems’ (ACSS) commercial name for the only FIM avionics in production at the time of this writing (2025). It contains a subset of the standard IM functions and has some functionality that differs from the industry standard. The SafeRoute+ avionics only accommodate two of the clearance types (i.e., Capture Then Maintain and Achieve-by Then Maintain), and they differ slightly from the standards invoked in TSO-C195c.
F.5.7.1 Maintain Current Spacing and Capture Then Maintain. In the absence of an ASG entry by the flightcrew, the SafeRoute+ FIM avionics calculate IM speeds to maintain the current spacing. A time or distance input must still be made by the flightcrew.
Appendix F F-9 F.5.7.2 Achieve-by Then Maintain. A SafeRoute+ Achieve-by Then Maintain clearance differs from the standards in two ways. It does not accept the lead aircraft’s planned route; therefore, the lead aircraft and IM aircraft must be flying direct to a common merge point.
F.5.7.3 No IM Suspend. SafeRoute+ does not include a “suspend” function. Instead, the pilot uses the “terminate” (also known as “cancel”) function.
Table F-2. Interval Management Clearance Types Summarized
Clearance Type Maintain Capture Then Maintain Cross Final Approach Spacing Notional Phraseology “TRAIL 456 Maintain distance behind LED123” “TRAIL 456 Maintain 90 seconds behind LED123” (or “Maintain 10 miles”) “TRAIL 456 Cross HONEE 90 seconds behind LED123 on the BRAVO transition. Cancel at LASFX.”
“TRAIL 456 Cross GOSER 90 seconds behind LED123” Clearance Elements Lead A/C FLT ID Lead A/C FLT ID Lead A/C FLT ID Lead A/C FLT ID ASG (implied) ASG ASG ASG CP Lead aircraft planned route if different than the IM aircraft planned route Lead aircraft planned route if different than the IM aircraft planned route PCP (optional) PCP (optional) PCP PCP defaulted Notes Underline indicates clearance type cue.
Not in SafeRoute+.
Underline indicates clearance type cue.
Lead aircraft is on different route— “BRAVO” transition.
Not in SafeRoute+.
F.6 IM Procedure. ATC may initiate an IM operation when operationally beneficial. The IM operations will proceed as follows:
F.6.1 ATC Identifies IM Pair. Using automation support tools, ATC identifies the potential IM lead aircraft and IM aircraft, ASG, CP (when applicable), and PCP.
F.6.2 ATC Checks Feasibility. ATC, supported by automation, determines the feasibility of the IM operation. Some of the factors used in this determination are current spacing, remaining distance, conflicting traffic, and weather.
F.6.3 ATC Issues IM Clearance. ATC issues the IM clearance to the IM aircraft flightcrew using one of the four clearance types.
Appendix F F-10 F.6.4 IM Flightcrew Reads Back Clearance. The IM aircraft flightcrew reads back the IM clearance and enters the IM clearance information into the FIM avionics.
F.6.5 IM Flightcrew Verifies Lead Aircraft. The flightcrew verifies that they have selected the correct lead aircraft and that they have entered the IM clearance elements correctly.
F.6.5.1 FLT ID Verification. Verifying the correct lead aircraft is an essential step.
It can be complicated by two factors. The first factor is that the telephonic or spoken call sign of the lead aircraft might not easily translate into the FLT ID displayed by the FIM avionics. For example, “Brickyard” does not readily translate to “RPA.” The second factor is that the lead aircraft or nearby nonparticipating aircraft might have erroneously programmed their FLT ID in their ADS-B Out system. The flightcrew should not accept the IM clearance if there is any doubt that they have correctly identified the lead aircraft as that given in the IM clearance.
F.6.6 FIM Avionics Internal Check. The FIM avionics perform an internal check to ensure all performance criteria are met. If the performance criteria are met, the FIM avionics display the first IM speed.
F.6.7 IM Flightcrew Evaluates IM Speed. The flightcrew evaluates the IM speed to determine whether it is acceptable given operational considerations, such as ride conditions and own aircraft limitations.
F.6.7.1 Rejected Clearance. If the flightcrew determines that the IM speed is unacceptable, they will immediately notify ATC that they are unable to accept the IM clearance.
F.6.7.2 Accepted Clearance. If the flightcrew determines that the IM speed is acceptable, they begin complying with the IM speeds with no further instruction by ATC (i.e., further read-back or reporting the implementation of each IM speed). ATC does not require any further acknowledgment by the flightcrew that they have accepted the IM clearance. This is similar to acknowledging a clearance to descend or climb; ATC expects the flightcrew to promptly comply or notify ATC that they are unable to comply.
F.6.8 IM Flightcrew Flies IM Speeds. The FIM avionics calculate IM speeds to maintain or achieve the ASG. In the case of an Achieve-by Then Maintain (also known as “Cross”) clearance, the IM speeds are flown to achieve the ASG by the time the IM aircraft reaches the CP. In the case of a Capture Then Maintain clearance, the IM speeds are flown to achieve the ASG quickly and then maintain that ASG until reaching the PCP.
F.6.8.1 Compliance With IM Speeds. It is important to emphasize that flightcrews should resist the temptation to “out-guess” the FIM algorithm by flying speeds other than the IM speed. Flying the IM speeds is how the flightcrew complies with the ATC-issued IM clearance. The FIM algorithm is designed to account for speed changes that result from the lead aircraft trajectory as well as actual winds encountered along the IM aircraft’s route, which inevitably will differ
Appendix F F-11 from the forecast winds entered in the FIM avionics. Not complying with the IM speed will make precise IM spacing more difficult and could lead to the need to fly more IM speeds than necessary.
F.6.8.2 Mandatory Published Speeds. The mandatory speeds published on STAR procedure charts are designed to condition the flow of traffic into the terminal arrival area. They are the basis for the speed profile used by the FIM avionics to calculate estimated times of arrival (ETA) at CP when using an Achieve-by Then Maintain clearance type and to calculate speed limits on the IM speed.
The IM speeds supersede the published speeds when operating on an IM clearance. Published speeds are used by the FIM avionics in the calculation of the trajectory of the lead aircraft and, hence, the IM speeds. Flightcrews need to continue to comply with the IM speed unless directed by ATC.
F.6.8.3 Compliance With Operational or Regulatory Speed Restrictions. It is the flightcrew’s responsibility to ensure that each IM speed does not conflict with any operational or regulatory speed restrictions. IM speeds do not supersede regulatory speed restrictions, such as 250 knots indicated airspeed (KIAS) below 10,000 feet mean sea level (MSL) in the United States. They also do not supersede the aircraft’s various operational speed restrictions. FIM avionics will limit IM speeds to within the operational limits of the aircraft, and not conflict with regulatory speed limits described here.
F.6.9 IM Cancellation. The IM aircraft flightcrew complies with the IM speeds until the procedure is canceled. When the IM operation is canceled, the FIM avionics no longer provide IM speeds or alerts. Upon IM cancellation, the flightcrew complies with speeds as instructed by ATC, as published, or as the last IM speed displayed. The IM operation will be canceled in one of the following ways:
• Automatically by the FIM avionics upon reaching the PCP;
• Manually by the flightcrew upon ATC instruction;
• Manually by the flightcrew for other operational reasons (which must be followed with a report to ATC); or
• Automatically due to certain off-nominal situations (which must be followed with a report to ATC if the flightcrew determined the operation needed to end).
F.7 Off-Nominal Situations. The IM procedure depends upon multiple factors: accurate wind and temperature profiles, close adherence to IM speed, and both aircraft adhering to their planned flight profiles. FIM avionics incorporate internal checks that verify that the horizontal navigation path of the IM aircraft and the lead aircraft are in acceptable limits for the IM procedure. Speed compliance monitoring by the FIM avionics assists the IM aircraft flightcrew with implementing the displayed IM speed. In the event the flightcrew is unable to continue conforming to the IM clearance by flying the IM speeds, they must notify ATC.
Appendix F F-12 F.8 IM Flight Planning. IM flight planning should take into consideration the capabilities of the aircraft, flightcrew, and air navigation service providers (ANSP) where IM is conducted. ATC will need to know in advance which aircraft are FIM-equipped and that the flightcrew is approved to conduct IM. To facilitate this, correct aircraft equipment codes will need to be entered on the flight plan (FP).
F.8.1 IM Outside the U.S. NAS. In the future, ANSPs outside the United States may conduct IM. Before conducting IM operations outside the U.S. NAS, determine whether the destination ANSP provides IM services that are compliant with existing ICAO guidance.
F.8.2 FP Codes. The FAA is adopting ADS-B In FP capability indicators for ADS-B In operations that require specific equipment, training, and authorization. The capability indicators tell ATC that the necessary equipment is on board the aircraft and operable, and that the flightcrew is qualified and authorized to conduct the indicated ADS-B In operations. When authorized and equipped to conduct IM using ACSS SafeRoute+, enter “SUR/I0” in FP Item 18 and ensure that the ADS-B capability code entered in FP Item 10 reflects ADS-B In capability. Refer to the Aeronautical Information Manual (AIM), Chapter 5, Air Traffic Procedures, for complete instructions on filing ADS-B equipment codes.
F.9 Authorization to Conduct IM. FAA authorization is required for all U.S. aircraft operators to conduct IM operations using ADS-B In (14 CFR § 119.49(a)(5)). For FAA authorization, refer to FAA Order 8900.1, Volume 3, Chapter 18, Section 3, Operations Specification (OpSpec)/Management Specification (MSpec)/Letter of Authorization (LOA) A355, Automatic Dependent Surveillance-Broadcast (ADS-B) In Operations.
F.9.1 Initial Request for Authorization. U.S. aircraft operators seeking to conduct IM should first contact their assigned FAA office to indicate their intent. At the time of the operator’s initial request, the FAA will provide the operator with an IM Application Checklist, which should be completed with attached supporting documents.
F.9.2 Documentation to Submit With Formal Request. This paragraph describes the documentation to be submitted with a formal IM proposal.
F.9.2.1 Request Letter. The operator’s assigned principal inspector (PI) may ask for additional information based on any unique aspects of their specific operation.
The operator should submit a letter of request for issuance of authorization to the assigned PI. The letter may be in a form acceptable to the Administrator
(e.g., as an electronic document entered into the Operations Approval Portal System (OAPS)). The letter of request should include the following information:
• Type of aircraft (make, model, and series (M/M/S)).
• List of aircraft registration numbers (N-number) associated with the request for authorization.
Appendix F F-13
• ADS-B equipment complies with TSO-C195c or later revision, or as approved for IM by the Administrator.
• Installation was completed following guidance contained in AC 20-165, Airworthiness Approval of Automatic Dependent Surveillance - Broadcast OUT Systems, and AC 20-172, Airworthiness Approval for ADS-B In Systems and Applications, or other acceptable means.
• Name of the ADS-B In (IM) software manufacturer and applicable software version(s).
• Intended areas of IM operations, listed by ANSP.
F.9.2.2 Airplane Flight Manual (AFM) Compliance Documentation. Operators will submit documentation that demonstrates applicable aircraft have an ADS-B In system that meets the performance standards of TSO-C195c or later revision, or as otherwise approved by the Administrator, for IM operations.
F.9.2.3 Operation Manuals and Checklists. The certificate holder (CH)/operator/program manager (as applicable) should submit information
(e.g., Airplane Operations Manual (AOM) bulletin or equivalent) to the flightcrews describing ADS-B, to include:
• IM system description;
• Normal procedures; and
• Non-normal or contingency procedures.
F.9.2.4 Maintenance Documentation. See Appendix C, ADS-B In Operations— Aircraft Qualification and Maintenance, for applicable maintenance guidance.
F.9.2.5 Revision of Minimum Equipment List (MEL). See Appendix C for guidance on the necessary MEL documents to be submitted for authorization of IM.
F.9.2.6 Pilot Training. Submit applicable portions of proposed IM-specific pilot training material and include a description of the methods used to conduct, evaluate, and manage the training. The IM pilot training should include:
1. ADS-B Out/In system overview (if not previously addressed with another ADS-B application).
2. ADS-B IM system operations.
3. IM normal procedures:
• Understanding IM clearance types and clearance elements.
• Compliance with IM speed.
Appendix F F-14
• Response to IM alerts.
• Lead aircraft FLT ID verification.
• Crew coordination during IM.
4. IM MEL procedures (as applicable).
5. IM equipment limitations.
6. CDTI interface.
7. Contingency procedures.
F.9.2.7 Dispatch/Flight Follower Training. Submit applicable portions of proposed IM-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. The training material should include:
1. General understanding of ADS-B In operations.
2. Correct flight planning codes for IM operations, including the ACID. A correct ACID in the FP is essential to the IM operation. Before ATC can commence an IM operation, the transmitted FLT ID from the lead aircraft must exactly match that from the FP. While filing ACID refers directly to the ADS-B Out aircraft, it can adversely impact an IM operation.
3. Dispatch of aircraft with the FIM system unserviceable.
4. How flight planning codes are affected with ADS-B or FIM avionics unserviceable.
5. Equipment needed to conduct IM.
6. ANSPs and airspace where IM operations are approved.
Appendix G G-1 APPENDIX G. CDTI ASSISTED SEPARATION ON APPROACH
CONTENTS Paragraph Page
G.1 PurposeG-3
G.2 BackgroundG-3
G.3 CAS-A ConceptG-3
G.3.1 CAS-A Concept—Ground ComponentG-3
G.3.2 CAS-A Concept—Airborne ComponentG-3
G.3.3 Notional PhraseologyG-4
G.4 CAS-A TerminologyG-4
G.4.1 Cockpit Display of Traffic Information (CDTI) Assisted Separation
on Approach (CAS-A) AircraftG-4
G.4.2 Cockpit Display of Traffic Information (CDTI) Assisted Separation
on Approach (CAS-A) AvionicsG-4
G.4.3 Designated TrafficG-4
G.4.4 Flight Identification (FLT ID)G-4
G.4.5 Selected TrafficG-4
G.5 CAS-A Communications DescribedG-4
G.6 CAS-A ProcedureG-4
G.6.1 Controller Identifies CAS-A TTF AircraftG-5
G.6.2 Flightcrew Reads Back the Designation InstructionG-5
G.6.3 Flightcrew Verifies TTF AircraftG-5
G.6.3.1 FLT ID VerificationG-5
G.6.3.2 CAS-A Avionics Performs Internal ChecksG-5
G.6.3.3 Flightcrew Confirms TTF Designation With the ControllerG-5
G.6.4 Controller Issues Instruction to Follow the Designated Traffic Along
With Approach ClearanceG-6
G.6.4.1 Accepted CAS-A Instruction to Follow the Designated TTFG-7
G.6.4.2 Rejected ClearanceG-7
G.6.5 Flightcrew Flies Normal Approach ProcedureG-7
G.6.6 CAS-A CancellationG-7
G.7 CAS-A AlertingG-7
G.7.1 Selectable Range IndicationG-7
Appendix G G-2
G.7.2 Minimum Range AlertG-7
G.8 Off-Nominal SituationsG-8
G.9 CAS-A FP CodesG-8
G.10 Authorization to Conduct CAS-AG-8
G.10.1 Initial Request for AuthorizationG-8
G.10.2 Documentation to Submit With Formal RequestG-8
G.10.2.1 Request LetterG-8
G.10.2.2 Airplane Flight Manual (AFM) Compliance DocumentationG-9
G.10.2.3 Operation Manuals and ChecklistsG-9
G.10.2.4 Maintenance DocumentationG-9
G.10.2.5 Revision of Minimum Equipment List (MEL)G-9
G.10.2.6 Pilot TrainingG-9
G.10.2.7 Dispatch/Flight Follower TrainingG-10