Detailed working notes on the ICAO Trajectory-Based Operations (TBO) concept. This folder expands the summary in topics/tbo.md into per-aspect files so each can be read independently.

Files in this folder#

• overview.md — what TBO is, where it sits in the ICAO/ATM framework, and why the concept matters for global modernisation.
• components.md — the building blocks of TBO: trajectory states, functional axes, the negotiation protocol, and the data model.
• blocks.md — TBO maturity stages from initial 4D (i4D / TBO-B2) to full trajectory contracts (TBO-B3), and the ASBU block structure.
• threads.md — the functional axes that together constitute TBO and their inter-dependencies (FF-ICE, SWIM, datalink, PBN, MET, CDM).
• modules.md — anatomy of one TBO capability with worked examples: i4D with RTA, EPP downlink, and a trajectory contract scenario.
• enablers.md — CNS infrastructure, procedures, avionics, regulation, training, and institutional arrangements required for TBO.
• performance_objectives.md — KPA-keyed performance table and KPIs for TBO operations.
• timeline.md — historical evolution: ICAO concept origins, AN-Conf milestones, SESAR i4D trials, FF-ICE releases, ASBU block dates.
• references.md — consolidated ICAO and authoritative external references for all content in this folder.

Reading order#

Start with overview.md to understand the concept, then components.md for the structural building blocks, then blocks.md and threads.md for the ASBU architecture. modules.md provides concrete worked examples. Use enablers.md for planning checklists, performance_ objectives.md for KPA/KPI mapping, and timeline.md for date context. references.md is the citation master list.

Source basis#

Content is grounded in:

• ICAO Doc 9854 (Global ATM Operational Concept), 1st edition (2005).
• ICAO Doc 9965 (FF-ICE Manual), 1st edition.
• ICAO Doc 4444 (PANS-ATM), Chapter 13 and Appendix 5.
• ICAO Doc 9613 (PBN Manual), Volume I.
• ICAO Doc 10177 (Environment Manual), Chapter 8.
• ICAO Doc 10209 (AN-Conf/14 Report, 2022).
• ICAO Doc 10007 (AN-Conf/12 Report, 2012).
• ICAO GANP Portal: https://ganpportal.icao.int/

What TBO is#

Trajectory-Based Operations (TBO) is the ICAO operational concept in which the four-dimensional trajectory (latitude, longitude, altitude, and time — 4DT) of each flight becomes the primary shared planning and tactical reference between airspace users and air navigation service providers across the full gate-to-gate flight.

Under TBO, every flight maintains a agreed 4D trajectory that:

• Is established collaboratively before departure (desired trajectory submitted; constraints applied; agreed trajectory reached).
• Is kept current throughout the flight through renegotiation when conditions require.
• Is shared among all relevant ATM community members through the SWIM information environment.
• Serves as the primary input to separation planning, demand-capacity balancing, and network optimisation.

This replaces the reactive, position-centric ATM model with a predictive, trajectory-centric model in which the future location of every aircraft is known, shared, and managed in advance.

Where TBO sits in the ICAO/ATM framework#

TBO is simultaneously:

1. A component of the Global ATM Operational Concept (Doc 9854). Chapter 2 of Doc 9854 defines "management by trajectory" as one of the seven ATM concept components. The agreed trajectory agreement replaces the open-ended vector and extends through all physical phases of flight.

2. The headline operational thread of the ASBU framework (GANP / Doc 9750). TBO is the named operational ASBU thread with modules in Block 2 (initial TBO, from 2025) and Block 3 (full TBO, from 2031). It is the stated long-term destination of the GANP.

3. The operational beneficiary of the FF-ICE information model (Doc 9965). FF-ICE defines the five 4D trajectory states (desired, negotiating, agreed, aircraft, executed) and the information exchange processes that carry them. Without FF-ICE, TBO has no standardised information backbone.

4. A consumer of SWIM, PBN, datalink, and surveillance advances. TBO is the "reward" for the investment in SWIM services, ATN B2 data link, multi-constellation GNSS, and ADS-C. None of those enablers has full value without TBO as the target operational concept.

The conceptual shift: from position to trajectory#

Current ATM manages the present position of aircraft: radar shows where the aircraft is; controllers issue clearances to redirect it; the next sector does not know what trajectory will arrive until the strip or data transfer lands. TBO manages the future trajectory of aircraft:

Why TBO matters operationally#

TBO is the highest-leverage operational improvement available in the GANP for three reasons:

Efficiency. Delays are absorbed early (as a changed departure time or an RTA constraint) rather than late (as holding fuel). Actual trajectories more closely match user-preferred trajectories, reducing track miles and fuel burn.

Capacity. Trajectory-based separation management extends the planning horizon far beyond the radar picture. Conflicts are detected and resolved before they manifest, reducing controller workload and allowing higher sector throughput.

Predictability. When all parties share the same agreed 4D trajectory, arrival times at downstream sectors, TMAs, and airports become predictable. Network management, A-CDM, and AMAN all depend on this predictability.

Relationship to other topics in this workspace#

• FF-ICE — the information model that carries the trajectory; without FF-ICE/R2, full TBO is not realisable.
• SWIM — the information backbone that distributes the shared trajectory picture to all ATM community members.
• ASBU — TBO is the TBO thread within ASBU; its block dependency chain runs from SWIM-B1, FICE-B1, COMI-B1 to TBO-B2.
• ATFM / NOPS — TBO transforms ATFM: delays become trajectory constraints rather than ground delays; the network manager's DCB function operates on agreed trajectories.
• A-CDM — surface TBO and gate planning are the TMA/airport end of the gate-to-gate trajectory agreement.
• PBN — provides the navigation precision that makes precise waypoint timing (RTA) achievable in the FMS.
• AIDC — the near-term data link for ATS interfacility coordination; TBO extends this to full trajectory sharing.

References#

• Doc 9854 (Global ATM Operational Concept), Chapter 2, §2.8 — Management by trajectory as a core ATM concept component.
• Doc 9854, Chapter 2, §2.1.5 — Traffic synchronisation changes including dynamic 4-D trajectory control.
• Doc 9965 (FF-ICE Manual), Glossary and Chapter 3 — Trajectory state definitions and the FF-ICE information model underpinning TBO.
• Doc 9750 (GANP), ASBU Thread TBO — TBO as the headline operational ASBU thread (authoritative source — not in local library; see https://ganpportal.icao.int/).

TBO is not a single system or standard. It is a structured set of interlocking components that together deliver the trajectory-centric ATM model. The components are organised below.

1. The 4D Trajectory Data Model#

The foundational component is the formal definition of the 4D trajectory. Doc 9965 (FF-ICE Manual) defines the 4D trajectory as:

A four-dimensional (x, y, z, and time) trajectory of an aircraft from gate-to-gate, at the level of fidelity required for attaining the agreed ATM system performance levels.

The trajectory is built from a sequence of change points, each carrying:

• Position (published identifier, latitude/longitude, or place-bearing distance)
• Altitude constraint (at, at-or-above, at-or-below, block)
• Speed constraint (Mach, CAS, TAS)
• Required time of arrival (RTA) — the time at which the aircraft must, should, or may not be before/after the fix
• Leg type (fly-by, fly-over, radius-to-fix, holding)

FIXM (Flight Information Exchange Model) is the XML/GML data model that encodes the 4D trajectory for machine-machine exchange. FIXM is the payload inside FF-ICE messages and SWIM services.

2. Trajectory State Machine#

Doc 9965 defines five trajectory states that every flight transitions through. These states form the normative TBO state machine:

• Desired 4D trajectory — the airspace user's preferred gate-to-gate trajectory accounting for known constraints and user objectives. The user generates and maintains this; it is the starting bid.
• Negotiating 4D trajectory — a candidate trajectory proposed by either the airspace user or an ASP during the negotiation cycle. Multiple negotiating trajectories may exist in parallel; each party may hold only one at a time. These are transitory.
• Agreed 4D trajectory — the trajectory agreed between the airspace user and all relevant ASPs after collaboration, or after imposition of pre-agreed rules. Only one agreed trajectory exists per flight at any time. It is renegotiated when conditions require.
• Aircraft trajectory — what the aircraft actually intends to fly, determined by the FMS. In normal operations this remains within the agreed trajectory tolerances.
• Executed 4D trajectory — the actual flown trajectory recorded for performance analysis, conformance assessment, and safety review.

The transition from desired to agreed is the core TBO activity. When the agreed trajectory diverges from the aircraft trajectory (i.e. a conformance breach), the cycle re-engages.

3. Trajectory Negotiation Protocol#

The negotiation protocol is the process by which desired and negotiating trajectories converge to an agreed trajectory. The key steps are:

1. The airspace user files a desired 4D trajectory via FF-ICE (before departure or as conditions change).
2. Each relevant ASP independently validates the trajectory against its DCB constraints, airspace restrictions, and traffic demand.
3. If the trajectory is acceptable, the ASP accepts it, contributing to the agreed trajectory. If not, the ASP issues a trajectory constraint (e.g. an RTA at a metering fix, an altitude entry constraint, a re-route).
4. The airspace user generates a new negotiating trajectory meeting the constraints and resubmits.
5. Steps 2-4 iterate until all ASPs have accepted an end-to-end trajectory, at which point it becomes the agreed trajectory.

Doc 9965 Appendix C, §16 gives a worked multi-ASP negotiation scenario: ASP-1 provides airspace constraint information; ASP-2 requires an RTA and altitude entry constraint on the arrival route; the airspace user generates a new end-to-end negotiating trajectory meeting both sets of constraints.

4. ADS-C Conformance Monitoring#

Once the agreed trajectory is established, conformance monitoring is the mechanism that enforces it. ADS-C (Automatic Dependent Surveillance — Contract) provides:

• Periodic contract — position reports at defined intervals (used oceanic/remote where radar is absent).
• Event contract — reports triggered when defined parameters change (level change, when next waypoint changes, etc.).
• Extended Projected Profile (EPP) — a downlink of the FMS trajectory ahead, enabling ground systems to validate the aircraft's intended path against the agreed trajectory.

PANS-ATM Doc 4444 §13.1(f) cites intent validation using EPP data as an ADS-C ground system function: EPP data are compared with the current clearance and discrepancies identified. This is the current PANS-level foundation for trajectory conformance.

5. Required Time of Arrival (RTA) / Controlled Time of Arrival (CTA)#

RTA and CTA are the operational interfaces between ATM constraints and FMS execution:

• RTA (Required Time of Arrival) — a time constraint at a specified waypoint, generated by the FMS and achievable through speed adjustment within FMS performance limits. RTA is an FMS capability; the FMS solves for a speed schedule that meets the time constraint.
• CTA (Controlled Time of Arrival) — an ATC-issued time constraint at a metering fix, delivered via CPDLC. The aircraft uses its RTA function to fly the CTA.

The CPDLC message set in PANS-ATM Appendix 5 formally carries the RTA element: "For the specified position, provides the required time of arrival (hours, minutes), optionally any tolerance around the required time of arrival, and indicates the required time of arrival as at, before, or after the specified time."

i4D (Initial 4D) is the operationally deployed precursor to full TBO. In i4D, the only time constraint delivered is a CTA at a defined metering fix, typically the start of the STAR or a TMA entry point. The FMS uses its RTA function to fly it. SESAR demonstrated i4D in live trials from 2014. This is the stepping stone to full negotiated trajectory operations.

6. FF-ICE Information Framework#

FF-ICE (Flight and Flow — Information for a Collaborative Environment, Doc 9965) is the information framework through which trajectories are filed, negotiated, updated, and shared. FF-ICE has two releases aligned with ASBU blocks:

• FF-ICE/1 (Release 1 / FICE-B1) — planning-phase information exchange: filing the desired trajectory, receiving back the agreed trajectory, sharing the trajectory with all relevant parties.
• FF-ICE/R2 (Release 2 / FICE-B2) — execution-phase information exchange: real-time updates to the agreed trajectory during flight, trajectory renegotiation, EPP sharing.

FF-ICE/R2 is the full TBO information backbone. Together they replace the legacy filed flight plan with a living, shared flight information lifecycle managed through SWIM.

7. SWIM Information Backbone#

TBO depends on SWIM (System-Wide Information Management) to distribute the shared trajectory picture to all ATM community members. SWIM ensures that:

• The agreed trajectory is visible to all ASPs along the route.
• DCB (demand-capacity balancing) sees consistent trajectory data across FIR boundaries.
• ATFM constraints are communicated back to the airspace user through the same information fabric.
• AMET 4D wind data and aeronautical information updates are integrated into the trajectory planning environment.

8. Datalink Substrate (CPDLC and ADS-C)#

The air-ground data link is the communications layer that carries TBO messages between the FMS and ground systems:

• CPDLC (Controller-Pilot Data Link Communications) — delivers RTA/CTA constraints and trajectory updates from ground to cockpit and acknowledgements back. ATN B2 over VDL Mode 2 is the continental standard; FANS-1/A over ACARS/satcom covers oceanic and remote. ATN B2 is required for full TBO message capacity.
• ADS-C — returns EPP and position data from cockpit to ground. Oceanic ATM already uses ADS-C; continental TBO extends ADS-C EPP use for conformance monitoring.

Summary: the dependency chain#

PBN / GNSS
 navigation precision
        |
  FMS RTA capability
  (i4D stepping stone)
        |
   CPDLC ATN B2        ADS-C EPP
   (deliver RTA)       (return intent)
        |_____________________/
                  |
        Trajectory negotiation
         via FF-ICE / FIXM
                  |
        SWIM information sharing
         (all parties see same
          agreed trajectory)
                  |
          Agreed 4D trajectory
         = primary ATM reference

References#

• Doc 9965 (FF-ICE Manual), Glossary — formal definitions of all five trajectory states.
• Doc 9965, Chapter 3, §3.5.7–3.5.8 — trajectory synchronisation and separation provision in a trajectory-based environment.
• Doc 9965, Appendix C, §16 — worked multi-ASP trajectory negotiation scenario with RTA and altitude constraints.
• Doc 4444 (PANS-ATM), Chapter 13, §13.1(f) — ADS-C intent validation using extended projected profile (EPP) data.
• Doc 4444, Appendix 5 — CPDLC message set including required time of arrival (RTA) at named waypoints.
• Doc 9854 (Global ATM Operational Concept), Chapter 2, §2.8 — management by trajectory; the agreed trajectory as the ATM system reference.

How TBO maps to the ASBU Block structure#

TBO is the headline operational thread of the ASBU framework. Unlike most ASBU threads, TBO spans multiple blocks not as incremental improvements to the same capability but as distinct operational paradigms that depend on cumulative enabler maturity.

The progression from current operations to full TBO can be described as four stages:

Stage 0 — Current ATM (Pre-TBO baseline)#

Character. Aircraft are managed by current position. ATC issues clearances that redirect the aircraft from its present position to a new level, route, or speed. The "plan" is a filed flight plan (FPL2012 or ICAO FPL) that describes intent but is not actively managed or shared as a 4D trajectory. Information flows reactively.

Enablers in place. Mode S/SSR surveillance, voice CPDLC (FANS-1/A in oceanic), AIDC for data link coordination between adjacent units. ATIS and VOLMET for MET. Basic ATFM slots.

Limitation. The ATM system has no picture of the future trajectory beyond radar extrapolation. Network management operates on delay rather than trajectory adjustment. Handoffs rely on estimate messages. Predictability is poor; delays are managed by holding and speed control at the cost of fuel and emissions.

Stage 1 — Initial 4D (i4D), TBO-B1/B2 initial#

Availability. Precursor modules endorsed at AN-Conf/12 (2012); SESAR i4D live trials from 2014; aligns with ASBU Block 1/2 boundary.

Operational change. The FMS receives a CTA (Controlled Time of Arrival) via CPDLC at a defined metering fix — typically the TMA entry point or top of descent. The FMS uses its RTA function to compute a speed schedule that delivers the aircraft at that fix within the specified tolerance (typically plus or minus 30 seconds). Ground systems monitor ADS-C EPP to verify trajectory intent.

What this delivers. Arrival metering becomes precise. The AMAN can sequence traffic to a TMA entry fix with second-level accuracy, eliminating the speed-control uncertainty of voice metering. Predictability at the TMA entry point dramatically improves. Fuel savings come from fewer late speed changes and reduced vectoring.

Key message set. The PANS-ATM Appendix 5 CPDLC message set includes the "required time arrival" element used in i4D CTA delivery.

Dependencies. FMS with RTA capability; ATN B1/B2 or FANS-1/A data link for CTA delivery; AMAN with time-based metering tool; ADS-C EPP for conformance monitoring; controller training.

Stage 2 — Negotiated Trajectory Operations (TBO-B2)#

Availability. ASBU Block 2, from 2025.

Operational change. The airspace user files a full gate-to-gate 4D desired trajectory via FF-ICE/1. Relevant ASPs validate the trajectory and apply constraints (RTA at metering fixes, altitude entry constraints, re-routes where congestion requires). A negotiation cycle produces an agreed 4D trajectory shared via SWIM among all ASPs along the route. ADS-C EPP confirms in-flight conformance.

Network management changes form: instead of issuing ground delay programme slots, the ATFM unit issues RTA constraints on the agreed trajectory. The airspace user absorbs the delay as a slowed trajectory rather than holding on the ground.

What this delivers. Full gate-to-gate predictability. Network efficiency because delays are distributed optimally across the trajectory rather than absorbed as fuel-burning holding. Cross-border seamlessness because all ASPs share the same agreed trajectory. Significant reduction in controller workload from reactive conflict resolution.

Dependencies. FF-ICE/1 operational; SWIM services carrying trajectory data; ATN B2 data link (for full CPDLC TBO message set); ADS-C EPP; FMS with full 4D trajectory capability; FIXM data model. SWIM-B1 and FICE-B1 modules must be in place.

Stage 3 — Full TBO and Trajectory Contracts (TBO-B3)#

Availability. ASBU Block 3, from 2031.

Operational change. Full trajectory contracts replace the current model of clearances as the primary ATM reference. The agreed 4D trajectory is a formal contract between the airspace user and the ATM system: the user commits to fly the trajectory within defined tolerances; the ATM system commits to manage separation based on it. Automation-to-automation (A2A) negotiation allows FMS and ground trajectory planning systems to exchange trajectory updates without mandatory human intervention on routine conflicts, with humans overseeing and intervening on exceptions.

FF-ICE/R2 (Execution Information) provides the execution-phase information lifecycle: real-time trajectory updates, re-routing, EPP sharing, and collaborative conflict resolution as conditions evolve.

Fully performance-based surveillance and digital communication mean that voice is an exception. TBO integrates with remote tower services (RATS), advanced RPAS integration, and higher-airspace operations.

What this delivers. Near-optimal gate-to-gate trajectories for all flights. Minimum fuel burn consistent with network safety margins. The "one sky" envisioned in Doc 9854 — ATM operating on shared, high-fidelity trajectory information rather than fragmented local pictures.

Dependencies. FF-ICE/R2 operational; full SWIM federation; ATN B2 or next-generation data link with A2A message capacity; advanced FMS; space-based ADS-B or equivalent for global coverage; regulatory framework for automated trajectory negotiation; controller acceptance.

ASBU Block dependency for TBO#

TBO-B2 depends on:

• SWIM-B1 — operational SWIM services distributing trajectory data
• FICE-B1 — FF-ICE Release 1 (planning-phase information)
• COMI-B1 — ATN B1/B2 or FANS-1/A data link
• NAVS-B1 — mature PBN environment (RNP precision for RTA)
• AMET-B1 — IWXXM-based 4D meteorological data for FMS planning

TBO-B3 additionally depends on:

• FICE-B2 — FF-ICE Release 2 (execution-phase information)
• COMI-B2 — ATN/IPS migration; high-capacity data link
• SWIM-B2 — full SWIM with federated access and QoS
• NAVS-B2 — multi-constellation multi-frequency GNSS

References#

• Doc 9854 (Global ATM Operational Concept), Chapter 2, §2.1.5 and §2.8 — 4-D trajectory control and management by trajectory as ATM concept elements.
• Doc 9965 (FF-ICE Manual), Glossary — trajectory state definitions; Chapter 3, §3.5.7–3.5.8 — trajectory synchronisation and separation provision.
• Doc 4444 (PANS-ATM), Appendix 5 — CPDLC message set including required time of arrival element.
• Doc 10007 (AN-Conf/12 Report, 2012), Agenda Item 5, Recommendation 5/2 — endorsement of initial 4D TBO and Block 3 full TBO ASBU modules.
• Doc 9750 (GANP), ASBU Thread TBO — Block 2 and Block 3 TBO module definitions (authoritative source — not in local library; see https://ganpportal.icao.int/).

TBO is not a standalone capability. It is delivered by the convergence of six functional axes (threads) that must mature in parallel. This file maps those axes, their inter-dependencies, and the ASBU threads that underpin each one.

Thread 1 — Trajectory Definition and Exchange#

Purpose. Define the 4D trajectory data model to the fidelity required for TBO and establish the information exchange framework that carries it.

Key elements.

• The 4D trajectory data model (lateral route, vertical profile, speed schedule, time constraints) as defined in Doc 9965.
• FIXM (Flight Information Exchange Model) as the XML/GML encoding standard for trajectory data.
• FF-ICE/1 and FF-ICE/R2 as the lifecycle management framework (filing, validation, update, sharing).
• GUFI (Globally Unique Flight Identifier) providing a stable reference for all trajectory exchanges across the lifecycle.

ASBU mapping. FICE (FF-ICE) thread: FICE-B1 (planning information), FICE-B2 (execution information).

Dependency. This thread is the primary TBO information backbone. All other threads depend on it producing a well-formed, agreed 4D trajectory.

Thread 2 — Trajectory Negotiation and Synchronisation#

Purpose. Establish the process by which the desired 4D trajectory transitions to the agreed 4D trajectory and remains synchronised throughout the flight.

Key elements.

• Pre-departure filing (desired trajectory submitted via FF-ICE).
• Constraint application by ASPs (RTA, altitude entry, re-route).
• Negotiating trajectory exchange cycles until agreement is reached.
• In-flight re-negotiation when conditions require (weather, airspace closure, traffic demand surge).
• Traffic synchronisation (TS) function in Doc 9965 §3.5.7, which obtains flight information and provides constraints onto the trajectory to achieve flow objectives.

ASBU mapping. TBO thread: TBO-B2 (initial negotiation); TBO-B3 (automation-to-automation negotiation).

Key standard. Doc 9965 Appendix C §16 defines the multi-ASP trajectory negotiation protocol including RTA and altitude entry constraints.

Thread 3 — Conformance Monitoring#

Purpose. Verify that the executed trajectory remains within tolerances of the agreed trajectory and trigger corrective action when it does not.

Key elements.

• ADS-C periodic contracts for oceanic/remote position reporting.
• ADS-C event contracts triggered by FMS state changes (level change, waypoint change, off-route divergence).
• Extended Projected Profile (EPP) downlink: the FMS trajectory ahead compared against the agreed trajectory; discrepancies alert ground systems.
• Ground system intent validation (PANS-ATM §13.1(f) EPP function).
• Conformance alerts to controllers when tolerances are breached.
• Re-negotiation trigger when conformance cannot be restored.

ASBU mapping. ASUR thread (ADS-C component); COMI thread (data link for ADS-C).

Key standard. Doc 4444 Chapter 13 (ADS-C procedures); Appendix 5 (CPDLC message set for RTA delivery and trajectory updates).

Thread 4 — Network and CDM Integration#

Purpose. Integrate TBO into the network management and collaborative decision-making processes so that capacity constraints are expressed as trajectory constraints rather than slot delays.

Key elements.

• DCB (Demand-Capacity Balancing) operating on trajectory data: predicted demand is computed from agreed trajectories, not from estimates. RTA constraints replace ground delay programme slots for most capacity situations.
• ATFM measures expressed as trajectory constraints (RTA at sector boundary, altitude ceiling, re-route) and returned to the airspace user via the FF-ICE update mechanism.
• Integration of A-CDM milestone data (TOBT/TSAT) with the departure end of the agreed 4D trajectory so the surface and en-route trajectories form a single gate-to-gate plan.
• NOPS (Network Operations) and TBO are complementary: the network manager sees the agreed trajectory of all flights and can pre-emptively re-route or adjust timing before congestion builds.

ASBU mapping. NOPS thread; FICE thread (FF-ICE constraint return path); ACDM thread (CDM departure integration).

Thread 5 — Datalink Substrate#

Purpose. Provide the air-ground communications infrastructure that carries trajectory information, RTA constraints, and ADS-C data between FMS and ground systems.

Key elements.

• CPDLC ATN B2 — the continental data link for full TBO message capacity; delivers RTA constraints, trajectory update messages, and complex clearances. Requires ATN/IPS-capable ground network and approved avionics.
• FANS-1/A over ACARS/satcom — the oceanic and remote data link (Inmarsat, Iridium); FANS-1/A supports basic CPDLC and ADS-C; delivers CTA in i4D deployments.
• ADS-C — the uplink of trajectory intent (EPP) and periodic position reports; the conformance-monitoring return channel.
• SWIM-based trajectory services — ground-ground distribution of the shared trajectory picture via IP-based SWIM services; all ASPs access the same agreed trajectory.
• Future — Iris (ESA satellite data link), LDACS (L-band Digital Aeronautical Communications System) as higher-capacity successors to VDL Mode 2.

ASBU mapping. COMI thread: COMI-B1 (ATN B1/B2, FANS-1/A); COMI-B2 (ATN/IPS migration, satcom).

Thread 6 — 4D MET Wind Integration#

Purpose. Provide accurate and timely four-dimensional meteorological data — in particular wind and temperature at all flight levels — to enable the FMS to compute realisable RTA solutions and to enable ground trajectory predictors to accurately model the agreed trajectory.

Key elements.

• IWXXM (ICAO Meteorological Information Exchange Model) — the XML/GML format for SIGMET, METAR, TAF, and gridded MET data exchanged via SWIM.
• Probabilistic and ensemble 4D wind data providing uncertainty bounds to the FMS RTA solver; when wind uncertainty is high, the FMS widens its RTA tolerance.
• High-resolution gridded model output (NWP data) from meteorological watch offices, exchanged at SWIM-accessible quality.
• Integration of MET data into ground trajectory prediction engines (used for DCB and conflict detection).

ASBU mapping. AMET thread: AMET-B1 (IWXXM-based MET exchange); AMET-B2/B3 (probabilistic and ensemble MET for TBO).

Inter-thread dependency map#

The six TBO threads are not independent:

• Thread 1 (trajectory exchange) is the primary carrier; all other threads feed into or depend on it.
• Thread 2 (negotiation) depends on Thread 1 (it has no data without FF-ICE) and Thread 4 (constraint input from network management).
• Thread 3 (conformance) depends on Thread 5 (data link returns the EPP) and Thread 1 (the agreed trajectory is the conformance reference).
• Thread 4 (network/CDM) depends on Thread 1 (trajectory data as demand input) and Thread 2 (constraint return path).
• Thread 5 (datalink) is infrastructure; it enables Threads 1, 2, 3, and 4.
• Thread 6 (MET) feeds Thread 1 (wind data into trajectory calculation) and Thread 2 (realisable RTA bounds).

Full TBO requires all six threads to be mature simultaneously — which is why the ASBU dependency chain for TBO-B2 lists SWIM-B1, FICE-B1, COMI-B1, NAVS-B1, and AMET-B1 as prerequisites.

References#

• Doc 9965 (FF-ICE Manual), Chapter 3 — functional description of trajectory synchronisation, DCB, and separation provision.
• Doc 9965, Appendix C, §16 — multi-ASP negotiation scenario showing Threads 1 and 2 in operation.
• Doc 4444 (PANS-ATM), Chapter 13 and Appendix 5 — ADS-C and CPDLC procedures (Threads 3 and 5).
• Doc 9854 (Global ATM Operational Concept), Chapter 2 — management by trajectory and traffic synchronisation (Threads 2 and 4).
• Doc 10209 (AN-Conf/14 Report), §3.8–3.9 — SWIM and FF-ICE identified as priority TBO enablers (Threads 1 and 5).

What a TBO Module is#

In ASBU terminology a module is the smallest deliverable planning unit, at the intersection of a Block (time window) and a Thread (feature area). The TBO thread has modules at Block 2 (TBO-B2) and Block 3 (TBO-B3). For practical implementation planning, TBO modules are best understood through their constituent capabilities and their worked operational scenarios.

This file provides the anatomy of TBO capability units and three worked examples covering the main operational mechanisms:

1. i4D with a single CTA (initial 4D metering).
2. EPP downlink for oceanic conformance monitoring.
3. A full trajectory contract scenario across two ASPs.

Anatomy of a TBO capability#

Every TBO capability unit has the following structured elements (mirroring the GANP Portal anatomy for any ASBU module):

1. Operational improvement statement#

Plain-language statement of what changes. For TBO-B2: "The 4D trajectory is negotiated and agreed between the airspace user and relevant ASPs before departure and kept current in flight; trajectory conformance is monitored via ADS-C EPP; ATFM constraints are expressed as RTA at defined metering fixes rather than ground delays."

2. Performance objective and applicable KPAs#

The "why". TBO modules primarily target:

• Flight efficiency — actual trajectory closer to user-preferred; track-mile and vertical efficiency improve.
• Predictability — variance between planned and actual gate-to-gate times reduces.
• Capacity — separation workload and ATFM delay minutes decrease as demand-capacity balancing uses trajectory data.
• Environmental impact — fuel burn and CO2 per flight decrease.

3. Procedure element#

• PANS-ATM (Doc 4444) Chapter 13: ADS-C procedures and EPP conformance monitoring.
• PANS-ATM Appendix 5: CPDLC message set for RTA/CTA delivery.
• FF-ICE operational procedures (filing, negotiation, update).
• Regional SUPP amendments for TBO airspace and procedures.
• Contingency procedures when agreed trajectory cannot be met.

4. Technology element#

Ground side: TBO trajectory management system; AMAN with time-based metering; FF-ICE ground processing; SWIM-connected trajectory services; ADS-C ground system.

Air side: FMS with RTA function and 4D trajectory capability; CPDLC avionics (ATN B1/B2 or FANS-1/A); ADS-C avionics (periodic, event, EPP contracts).

5. Human performance element#

Controllers require training in trajectory-based conflict detection and resolution rather than reactive radar vectoring. They must understand trajectory intent information (EPP) and when to intervene versus rely on the trajectory contract. Pilots require familiarity with RTA/CTA operations and FMS trajectory management. New human-machine interface requirements arise for trajectory display and conformance alerting.

6. Dependencies#

For TBO-B2: SWIM-B1 (trajectory distribution), FICE-B1 (FF-ICE/1 filing and exchange), COMI-B1 (data link), NAVS-B1 (PBN precision), AMET-B1 (4D wind).

For TBO-B3: FICE-B2 (FF-ICE/R2 execution information), COMI-B2 (ATN/IPS), SWIM-B2 (federated SWIM).

Worked Example 1 — i4D with CTA at TMA Entry#

Scenario#

A medium-haul flight approaches a busy hub airport from a distance of 500 NM. The AMAN (arrival manager) at the destination has calculated a metering sequence and requires the flight to cross the TMA entry fix (e.g. a published STAR waypoint) at 14:32:00 UTC (tolerance plus or minus 30 seconds).

Process#

1. The ground TBO/AMAN system generates a CTA for the flight: "Arrive FIX at 14:32Z +/- 30 sec."
2. The ATCO or automated system transmits the CTA to the aircraft via CPDLC using the RTA message element: "AT [FIX] CROSS AT [1432] [+/- 0030]."
3. The FMS receives the CTA and activates its RTA function for that waypoint. The FMS solves for a speed schedule (adjusting cruise Mach number within defined limits) that achieves the fix at 14:32 within tolerance.
4. The aircraft flies the FMS-computed speed schedule. Ground receives ADS-C periodic position reports confirming adherence.
5. EPP data (if ADS-C EPP contract is active) shows the FMS's projected trajectory to the fix, allowing the ground system to verify intent before the fix.
6. If wind conditions change such that the RTA becomes infeasible, the FMS alerts the crew; the crew requests a revised CTA or accepts a new agreed crossing time via CPDLC.

Benefit#

The AMAN sequences with second-level accuracy at the TMA entry point, eliminating the 2-4 minute uncertainty of voice speed control metering. Vectoring inside the TMA is reduced. Fuel burn decreases because the aircraft can descend optimally (CDO) without late speed changes to maintain sequence.

Standards basis#

Doc 4444 PANS-ATM Appendix 5 (RTA message element); Doc 4444 Chapter 13 (ADS-C procedures); Doc 9965 §3.5.7 (trajectory synchronisation).

Worked Example 2 — EPP Downlink for Oceanic Conformance#

Scenario#

A long-haul flight is in oceanic airspace beyond secondary radar coverage. The oceanic ATC unit has received the flight's oceanic clearance (route, level, speed). An ADS-C agreement is established providing periodic position reports every 14 minutes and event contracts triggered by level or speed changes.

The ADS-C agreement includes an EPP contract: the FMS transmits its projected trajectory profile — the next 10 waypoints with estimated times and levels — as part of each position report.

Process#

1. The FMS generates the EPP with each ADS-C report, showing the intended trajectory ahead at the fidelity of the current FMS flight plan.
2. The oceanic ATC ground system receives the EPP and compares it against the oceanic clearance.
3. PANS-ATM §13.1(f) cites this as "intent validation": discrepancies between the EPP and the current clearance are flagged to the controller.
4. If the FMS has modified the route or level to avoid weather (e.g. pilot-initiated deviation), the EPP shows the deviation before the next voice position report. The controller can act earlier.
5. The EPP can also be used for downstream prediction: the sector ahead can see the flight's likely level and time at entry 30-60 minutes in advance.

Benefit#

Oceanic conformance monitoring moves from a 14-minute position report cycle to near-continuous intent visibility. Safety improves because deviations are detected earlier. Cross-ocean traffic synchronisation improves because downstream sectors have better trajectory predictions.

Standards basis#

Doc 4444 Chapter 13, §13.1(f) (EPP intent validation); Doc 4444 §4.11 (ADS-C reporting requirements); Doc 9965 trajectory state definitions (aircraft trajectory vs. agreed trajectory comparison).

Worked Example 3 — Full Trajectory Contract across Two ASPs#

Scenario#

A flight from airport A (FIR-1) to airport C via FIR-2 submits a desired 4D trajectory via FF-ICE before departure. The trajectory includes an optimum cruise at FL380, a direct route across FIR-2, and arrival at airport C at 09:45 local.

ASP-1 (FIR-1) has no objection to the flight's trajectory in its airspace. ASP-2 (FIR-2) has a constrained sector and requires the flight to cross the FIR-1/FIR-2 boundary at FL360 and to arrive at the STAR entry fix no earlier than 09:25.

Process (following Doc 9965 Appendix C §16)#

1. The airspace user submits the desired 4D trajectory. Both ASPs receive it via SWIM.
2. ASP-1 accepts the trajectory in its airspace.
3. ASP-2 issues two constraints via FF-ICE: boundary at FL360; RTA at STAR entry fix not before 09:25.
4. The airspace user's system (or crew) generates a new negotiating 4D trajectory that meets both constraints: crosses the boundary at FL360 (accepted suboptimal but within fuel reserves) and crosses the STAR entry at 09:26 (just within the constraint).
5. Both ASPs validate the negotiating trajectory against their own constraints and indicate acceptance.
6. The agreed 4D trajectory is now formally established end-to-end. It is shared via SWIM and forms the primary reference for both ASPs throughout the flight.
7. In flight, ADS-C EPP confirms the aircraft is tracking the agreed trajectory. At the boundary handoff, ASP-2 has the agreed trajectory and needs no estimate message.

Benefit#

Cross-border handoffs are seamless. Both ASPs work from the same agreed trajectory, eliminating the coordination cost of estimate messages and reducing the possibility of separation errors at the boundary. The airspace user knows in advance exactly what constraints apply and can plan fuel, alternate routing, and timing accordingly.

Standards basis#

Doc 9965, Appendix C, §16 (multi-ASP trajectory negotiation protocol); Doc 9965, §3.5.7 (trajectory synchronisation); Doc 4444 Chapter 13 (ADS-C conformance in the airborne phase).

How TBO modules become a national plan#

A State or ANSP implementing TBO follows these steps:

1. Confirm the prerequisite ASBU modules are in place or scheduled (SWIM-B1, FICE-B1, COMI-B1, NAVS-B1, AMET-B1 for TBO-B2).
2. Select the TBO capability tier appropriate to the operational environment (i4D at a busy TMA; oceanic EPP; cross-border negotiated trajectory).
3. Define the airspace and traffic scope: which arrival fixes are metered; which sectors participate in negotiation; which cross-border agreements are needed.
4. Procure and certify the ground TBO system and update AMAN.
5. Mandate or coordinate equipage: CTA/RTA avionics, CPDLC, ADS-C.
6. Agree procedures with neighbouring FIRs for cross-border trajectory sharing.
7. Train controllers and operators.
8. Report progress against the regional ASBU implementation plan (e.g. APANPIRG for APAC, MIDANPIRG for MID, EANPG for EUR).

References#

• Doc 9965 (FF-ICE Manual), Appendix C, §16 — multi-ASP trajectory negotiation worked scenario.
• Doc 4444 (PANS-ATM), Chapter 13, §13.1(f) — ADS-C intent validation using EPP; Appendix 5, RTA message element.
• Doc 9854 (Global ATM Operational Concept), §2.8.10–2.8.11 — management by trajectory; clearance as incremental delivery of trajectory.

What an Enabler is#

An enabler is a supporting element without which a TBO module cannot deliver its intended benefit. TBO is notable among ASBU operational concepts for having an unusually long and tightly inter-dependent enabler chain. A State that invests in ground TBO systems without the matching fleet equipage, data link infrastructure, and procedural foundation will not see the predicted benefits.

AN-Conf/14 (2022, Doc 10209) Recommendation 3.1/3 explicitly calls on States to "expedite the implementation of trajectory-based operations enablers that are considered mature and relevant", and on ICAO to "develop ICAO provisions and guidance for automated air-ground trajectory synchronization". This underlines that enabler maturity is the current operational challenge.

1. Navigation — PBN and GNSS#

TBO requires that aircraft can fly a specified trajectory with predictable precision. PBN is the navigation foundation:

• RNP specification adherence — RTA metering only works if the aircraft track is predictable. RNP 1 or better in terminal areas; RNP 2 or A-RNP in en-route and oceanic environments.
• Multi-constellation GNSS — GPS plus Galileo, GLONASS, or BeiDou provides the receiver autonomy integrity monitoring (RAIM) availability needed for high-precision RTA.
• GBAS at major hubs — Cat I/III GBAS precision approaches ensure the ground phase of the gate-to-gate trajectory is equally precise.
• FMS trajectory capability — the FMS must support RTA on a nominated waypoint, maintain the speed schedule to meet the constraint within tolerance, and downlink the result via ADS-C.

Doc 9613 (PBN Manual) §1.6.1.1 explicitly states that PBN is expected to include 4D trajectory-based operations as a future evolution.

2. Air-Ground Data Link (CPDLC and ADS-C)#

Data link is the most critical near-term TBO enabler because it is the bottleneck between current (voice-based) and TBO operations.

• CPDLC ATN B1/B2 — delivers RTA/CTA constraints, trajectory update messages, and CPDLC clearances. ATN B1 (over VDL Mode 2) is the current European/continental standard. ATN B2 provides the extended message set needed for full TBO.
• FANS-1/A — the oceanic standard (over ACARS / Inmarsat / Iridium satcom). Supports basic CPDLC and ADS-C; can deliver i4D CTA.
• ADS-C — periodic contracts (position reporting), event contracts (level/speed change), and EPP (extended projected profile for intent validation). EPP is the critical TBO-specific ADS-C capability.
• VDL Mode 2 ground network — the ground-side data link infrastructure for ATN; requires ground station coverage along all TBO routes.
• ATN/IPS migration — the long-term evolution from ATN/OSI to IP-based ATN, enabling higher-capacity data link for Block 3 automation-to-automation negotiation.

3. Ground ATM Systems#

• TBO trajectory management system — the core ground platform that receives FF-ICE-filed desired trajectories, validates them, issues constraints, and manages the agreed trajectory lifecycle.
• AMAN with time-based metering — the arrival manager must support CTA/RTA outputs with time-slot accuracy to benefit from i4D.
• ADS-C ground system — receives EPP and position data from ADS-C contracts; performs intent validation per PANS-ATM §13.1(f).
• SWIM-connected services — publishes and subscribes to trajectory information via SWIM services, making the agreed trajectory visible to all relevant ATM actors.
• 4D trajectory prediction — ground trajectory predictors must use 4D meteorological data (winds, temperatures) to model the trajectory accurately; prediction errors create false RTA infeasibility alerts.

4. SWIM and Information Services#

TBO depends on the information environment being shared:

• SWIM operational services — flight information services (FF-ICE trajectory sharing), aeronautical information (AIXM), meteorological information (IWXXM), surveillance information — all available via SWIM for the ground TBO system.
• FF-ICE/1 operationalised — filing the desired trajectory and receiving the agreed trajectory require FF-ICE Release 1 to be operationally deployed. This is the FICE-B1 module prerequisite.
• FIXM-compliant ground systems — the trajectory payload must conform to FIXM (Flight Information Exchange Model) for interoperability across multiple ANSPs.

5. Meteorological Services (4D MET)#

• IWXXM gridded wind and temperature data — the FMS RTA solver requires accurate 4D wind/temperature to compute a feasible speed schedule for the RTA constraint. IWXXM as the SWIM exchange format is the AMET-B1 prerequisite.
• High-resolution NWP output — gridded model data at 0.25-degree or finer resolution, updated frequently (4-hourly or better).
• Uncertainty quantification — for Block 3 TBO, probabilistic wind data allow the RTA solver to compute a confidence interval and negotiate wider tolerances when uncertainty is high.

6. Avionics and Fleet Equipage#

TBO benefits are constrained to equipped flights. The enabling avionics are:

• FMS with RTA capability — the aircraft FMS must have an RTA function: the ability to target a defined crossing time at a nominated waypoint through speed adjustment.
• CPDLC avionics — ATN B1 or FANS-1/A data link terminal to receive CTA and return acknowledgements.
• ADS-C avionics — the aircraft system must support periodic, event, and EPP ADS-C contracts.
• Multi-constellation GNSS receiver — for the navigation precision required by RTA operations.
• Future: 4D trajectory-capable FMS — for full TBO, the FMS must accept a complete gate-to-gate 4D trajectory upload and manage it dynamically.

Equipage mandates for CPDLC and ADS-C have been implemented in several regions (European airspace — ATN B1 mandate; North Atlantic — FANS-1/A mandate for Oceanic airspace). TBO-specific equipage mandates are in progress.

7. Procedures and Standards#

• PANS-ATM amendments — Chapter 13 and Appendix 5 of Doc 4444 already contain the ADS-C and CPDLC/RTA foundations. Further amendments will formalise trajectory negotiation procedures.
• FF-ICE operational procedures — filing format, validation timelines, constraint communication, contingency when agreement cannot be reached.
• Contingency procedures — what controllers and crews do when the agreed trajectory becomes infeasible: who initiates renegotiation, what fallback separates traffic while negotiating.
• Regional SUPP (Doc 7030) — regional procedures for TBO airspace, CPDLC logon/logoff, ADS-C contract requirements.

8. Regulatory Framework#

• Operational authorisations — States must approve TBO operations under Annex 6 (Equipment carriage) and issue operational authorisations for CPDLC, ADS-C EPP, and RTA/CTA.
• Safety assurance — the TBO trajectory management system is a safety-critical system; SMS (Annex 19) integration and safety case development are required before service entry.
• Avionics certification — RTCA DO/EUROCAE ED MOPS define the minimum operational performance for RTA-capable FMS and ATN B1/B2 avionics.
• Cybersecurity — SWIM-connected trajectory systems are exposed to cyber risk; Annex 17 and ICAO cybersecurity framework apply.

9. Human Resources and Training#

• Controller training — trajectory-aware ATC: understanding EPP intent data; CTA/RTA issuance procedures; when to intervene versus rely on the trajectory; transition from radar vectoring to trajectory conformance monitoring.
• Pilot training — RTA/CTA FMS operation; understanding what happens when the FMS cannot meet the RTA; CPDLC message handling for trajectory-related messages.
• System operator training — ground TBO system operators (ATFM, network management) on trajectory-based DCB.

10. Institutional Arrangements#

• Cross-FIR trajectory agreements — LOAs (letters of agreement) between adjacent ANSPs for trajectory sharing, constraint application, and negotiation protocols across FIR boundaries.
• Regional planning fora — APANPIRG (APAC), MIDANPIRG (MID), EANPG (EUR) must endorse harmonised TBO implementation sequencing to avoid incompatible regional standards.
• FF-ICE bilateral readiness — technical and operational readiness of neighbouring ANSPs for FF-ICE exchange is a prerequisite for cross-border trajectory negotiation.
• Network manager / ATFM body — a regional or global network management function must be capable of expressing ATFM measures as trajectory constraints rather than slots.

References#

• Doc 10209 (AN-Conf/14 Report), Recommendation 3.1/3 — ICAO and States to expedite TBO enabler implementation and automated trajectory synchronisation provisions.
• Doc 9613 (PBN Manual), §1.6.1.1 — PBN as navigation enabler of TBO.
• Doc 4444 (PANS-ATM), Chapter 13 — ADS-C procedures; Appendix 5 — CPDLC RTA message element.
• Doc 9965 (FF-ICE Manual), Chapter 3 — trajectory synchronisation and information enablers.
• Doc 9854 (Global ATM Operational Concept), §2.8.10 — management by trajectory requiring gate-to-gate agreement.

The performance case for TBO#

TBO is justified not as a technology deployment but as a performance improvement. Every element of the TBO concept — trajectory negotiation, RTA metering, EPP conformance monitoring, FF-ICE information exchange — exists to improve one or more of the Key Performance Areas defined in Doc 9854 and Doc 9883.

Doc 10177 (Environment Manual) §8.3.3 records that TBO "seeks to improve operational predictability through more accurate and efficient end-to-end strategic planning and scheduling." Doc 10209 (AN-Conf/14) §3.8 records that the conference noted TBO benefits in "improving the predictability of aircraft movement and flight efficiency, as well as in increasing utilization of available airspace and aerodrome capacity and operator flexibility" — and recognised that "these benefits would contribute to achieving the ICAO LTAG for international aviation of net-zero carbon emissions by 2050."

KPA performance table#

The table below maps each primary KPA to the TBO performance objective, the Key Performance Indicator (KPI), and the TBO maturity stage at which the improvement is principally delivered.

KPA contribution by maturity stage#

The matrix below scores each KPA by its principal benefit horizon across the TBO maturity stages (1 = some benefit, 2 = clear benefit, 3 = primary driver). It is editorial, but it conveys where each stage's centre of gravity lies.

Detailed KPI definitions#

Flight efficiency KPIs#

KEA (Key Performance Indicator — Actual Extension). The ratio of actual flight distance to the great-circle distance. TBO reduces KEA by enabling user-preferred direct routings in the negotiated trajectory rather than fixed ATS routes.

Vertical profile efficiency. The proportion of flight time spent at or close to the optimum cruise altitude. TBO improves this by integrating the ATFM function with trajectory negotiation: delays are absorbed as ground-hold time rather than stepped level restrictions.

CDO conformance rate. The proportion of flights performing a continuous descent from top of descent to touchdown without level-off. i4D RTA metering at TMA entry is a direct enabler: the sequence is stabilised before the aircraft starts descent, removing the need for late speed changes and level-off.

Predictability KPIs#

RTA tolerance achievement rate. The proportion of i4D flights that cross the designated metering fix within the specified RTA tolerance (typically plus or minus 30 seconds). SESAR i4D trials in live operations achieved over 95% compliance. This is the headline KPI for Stage 1 TBO.

Arrival predictability variance. Standard deviation of actual landing time versus predicted landing time at a planning horizon of 20-40 minutes. TBO aims to reduce this from the current 3-5 minute variance (at a 20 NM planning horizon) to under 1 minute at the same horizon.

Capacity KPIs#

ATFM delay minutes per flight. TBO transforms ATFM from slot assignment (ground delay) to trajectory constraint (RTA adjustment). This improves sector utilisation because delays are distributed optimally along the trajectory rather than absorbed entirely at departure. The GANP target is a sustained reduction in network-average ATFM delay.

Controller workload (tactical interventions per sector). In a mature TBO environment, trajectory-based conflict detection and automation-assisted resolution reduce the tactical workload. This KPI is measured as the number of ATC instructions per flight in the sector.

Environmental KPIs#

Gate-to-gate fuel burn. TBO reduces fuel burn through three mechanisms: (a) optimised cruise trajectory (user-preferred routing); (b) reduced holding fuel (RTA absorbs delays before flight or early in cruise); (c) CDO from TMA entry (no level-off). Doc 10177 §8.3.4 attributes reductions in flight time, track miles, and low-altitude holding pattern use to TBO.

Excess fuel on arrival (CDO conformance proxy). Comparison of actual fuel used on approach versus optimal CDO fuel burn. An improvement in CDO conformance rate drives a measurable reduction in excess fuel per arrival.

Performance measurement framework#

TBO performance is reported through:

• ICAO GANP Review — global ASBU implementation monitoring reports, reviewed on a 3-year cycle aligned with the Assembly.
• Regional performance frameworks:
  • APAC — APANPIRG performance reporting against the Seamless ATM Plan metrics.
  • EUR — EUROCONTROL Performance Review Body; KPI-Actual Extension (KEA/KEP) published annually for the ECAC area.
  • NAT — ICAO North Atlantic tracks performance against RNP/RNAV and trajectory conformance metrics.
  • FAA NextGen — US FAA publishes TBFM (Time-Based Flow Management) performance metrics including RTA achievability rates and AMAN efficiency.
• SESAR 3 JU — SESAR Key Performance Indicators for i4D deployments, published in the European ATM Master Plan.

Why performance evidence matters for TBO funding#

Doc 9587 requires business-case justification for ASBU module investments. The performance evidence chain — KPA to Performance Objective to KPI to Module — is the required language of that business case. A State proposing investment in a TBO trajectory management system must quantify the expected improvement in KEA, predictability variance, and ATFM delay against the investment cost.

ICAO has committed (under AN-Conf/14 Recommendation 3.1/3(c-e)) to develop KPI guidance for TBO and to develop ICAO provisions for automated air-ground trajectory synchronisation — both of which are prerequisites for credible TBO business cases globally.

References#

• Doc 9854 (Global ATM Operational Concept), Chapter 2, §2.1.5 — traffic synchronisation KPA improvements through 4-D trajectory control.
• Doc 9883 (Manual on Global Performance of the Air Navigation System) — KPA definitions and the global performance management methodology.
• Doc 10177 (Environment Manual), Chapter 8, §8.3.3–8.3.4 — TBO contribution to fuel efficiency, noise reduction, and predictability.
• Doc 10209 (AN-Conf/14 Report), §3.8 and Recommendation 3.1/3 — conference endorsement of TBO KPI development and performance objectives.
• Doc 9587 (Economic Regulation Manual) — business-case requirement for ASBU module investment (authoritative source — not in local library; cited by reference).

Two timelines to keep distinct#

1. Concept and standards development — when ICAO and regional programmes defined, demonstrated, or standardised TBO elements.
2. ASBU Block availability — the notional dates from which TBO modules become globally implementable.

A State's own TBO implementation timeline is a third axis; it must be expressed against Block availability dates and the regional plan milestones.

TBO concept and standards timeline#

ASBU Block availability for TBO#

Regional implementation context#

Europe (SESAR 3 JU / Digital European Sky). SESAR pioneered i4D with live trials from 2014. The European ATM Master Plan (current issue) positions i4D as an initial deployment step and full TBO as the long-term target. ATN B1 mandate in European airspace provides the data link foundation. FF-ICE/1 readiness work is ongoing through the SESAR 3 JU programme.

United States (FAA NextGen). FAA TBFM (Time-Based Flow Management) is the US operational realisation of CTA-based arrival metering — an i4D equivalent. TBFM is operational at all major US airports. FAA NextGen TBO ConOps extends this toward full gate-to-gate trajectory management.

Asia-Pacific (APAC). AN-Conf/14 (2022) noted a working paper from China, Indonesia, Japan, New Zealand, Republic of Korea, Singapore, Thailand, and the United States on APAC pathways to TBO. APANPIRG monitors ASBU implementation annually. Priority is SWIM and FF-ICE/1 enabler deployment.

Middle East (MID). MIDANPIRG tracks ASBU implementation. TBO enablers (SWIM, CPDLC) are progressing through the MID Air Navigation Strategy.

Global. AN-Conf/14 Recommendation 3.1/3 is the current global mandate. ICAO is developing provisions for automated air-ground trajectory synchronisation and KPI guidance for TBO as follow-up actions.

How to read a date in a TBO document#

When a TBO-related document uses a date, verify which kind it is:

• "Block 2 from 2025" — ASBU block availability (globally implementable from that date; not a deadline).
• "TBO deployment by 2030" — national or regional commitment.
• "AN-Conf/14 (2022)" — ICAO conference year.
• "SESAR i4D trial 2014-2016" — programme-specific trial date.

Mixing these categories leads to false impressions of implementation progress or delay.

References#

• Doc 9854 (Global ATM Operational Concept), 1st edition (2005) — management by trajectory concept origin.
• Doc 9965 (FF-ICE Manual), 1st edition (2007) — 4D trajectory state model origin.
• Doc 10007 (AN-Conf/12 Report, 2012) — TBO ASBU modules endorsed.
• Doc 10209 (AN-Conf/14 Report, 2022), §3.7–3.9 and Recommendation 3.1/3 — latest ICAO mandate for TBO implementation.
• Doc 9750 (GANP), editions 4–7 — ASBU block date history and TBO thread evolution (authoritative source — not in local library; see https://ganpportal.icao.int/).
• SESAR 3 JU / Digital European Sky — i4D trial history (authoritative source — not in local library; see https://www.sesarju.eu/).
• FAA TBFM — US operational CTA metering deployment (authoritative source — not in local library; see https://www.faa.gov/nextgen/programs/tbfm).

Primary ICAO documents#

• Doc 9854 — Global Air Traffic Management Operational Concept, 1st edition (2005). Source of the "management by trajectory" concept and the seven ATM concept components. Chapter 2, §2.8 is the foundational TBO text.
• Doc 9965 — Manual on Flight and Flow — Information for a Collaborative Environment (FF-ICE), 1st edition. Defines the 4D trajectory state model (desired, negotiating, agreed, aircraft, executed) and the FF-ICE information framework; Appendix C §16 contains the multi-ASP trajectory negotiation worked scenario.
• Doc 4444 — PANS-ATM (Procedures for Air Navigation Services — Air Traffic Management). Chapter 13: ADS-C procedures including EPP intent validation (§13.1(f)). Appendix 5: CPDLC message set including the required time of arrival (RTA) element.
• Doc 9613 — Performance-Based Navigation (PBN) Manual. Volume I, §1.6.1.1: "In the future, PBN is expected to include 4D trajectory-based operations (TBO)." The navigation enabler basis for TBO.
• Doc 10177 — Environment Manual. Chapter 8, §8.3.3–8.3.4: TBO benefits for predictability, noise mitigation, fuel efficiency, and capacity.
• Doc 10209 — Report of the Fourteenth Air Navigation Conference (AN-Conf/14, 2022). §3.7–3.9: conference discussion of TBO; Recommendation 3.1/3: States to expedite TBO enablers; ICAO to develop automated air-ground trajectory synchronisation provisions.
• Doc 10007 — Report of the Twelfth Air Navigation Conference (AN-Conf/12, 2012). Agenda Item 5, Recommendation 5/2: endorsement of ASBU modules for initial 4D TBO (Block 1) and full 4D TBO (Block 3) as the strategic direction.
• Doc 9883 — Manual on Global Performance of the Air Navigation System. Defines KPA taxonomy and the global performance management methodology used to measure TBO benefits.
• Doc 9750 — Global Air Navigation Plan (GANP), 4th–7th editions. ASBU framework with TBO as the headline operational thread in Block 2 and Block 3 (authoritative source — not in local library; see https://ganpportal.icao.int/).

ICAO PANS and Annexes most relevant to TBO#

• Annex 10, Volume III — Aeronautical Telecommunications (Data Link). CPDLC standards and ADS-C communication standards.
• Annex 11 — Air Traffic Services. ATS provision; ADS-C definition (§6.2.3.2 for cross-border data link coordination); ADS-C agreement definition.
• Annex 10, Volume I — Radio Navigation Aids. GNSS standards underpinning the navigation precision required for RTA operations.
• Annex 6, Part I — Operation of Aircraft. Equipment carriage requirements relevant to TBO avionics (CPDLC, ADS-C, FMS RTA).
• Annex 19 — Safety Management. SMS requirements for TBO systems as safety-critical ground installations.

ICAO documents on related enablers#

• Doc 9039 / Doc 10039 — Manual on System-Wide Information Management (SWIM). SWIM as the information backbone distributing the agreed trajectory to all ATM community members.
• Doc 9368 / FF-ICE Implementation Guidance Material (2020). Operational procedures for FF-ICE/1 filing and trajectory exchange.

Live / authoritative sources#

• ICAO GANP Portal — https://ganpportal.icao.int/ — live home of the ASBU framework; TBO thread under operational threads.
• ICAO AN-Conf/14 (2022) documentation — https://www.icao.int/Meetings/anconf14/Pages/default.aspx

Regional implementation references#

• European ATM Master Plan (SESAR 3 JU / Digital European Sky) — i4D as initial TBO deployment; full TBO as long-term target. https://www.sesarju.eu/projects/digital-european-sky (authoritative source — not in local library)
• FAA Time-Based Flow Management (TBFM) — US operational CTA/RTA arrival metering. https://www.faa.gov/nextgen/programs/tbfm (authoritative source — not in local library)
• FAA NextGen TBO ConOps — strategic direction for US trajectory-based operations. https://www.faa.gov/nextgen (authoritative source — not in local library)
• EUROCONTROL TBO concept page — implementation guidance for European TBO deployments. https://www.eurocontrol.int/concept/trajectory-based-operations (authoritative source — not in local library)
• APAC Seamless ATM Plan (ICAO Asia/Pacific Regional Office) — APAC ASBU implementation roadmap including TBO enabler progression.
• MID Air Navigation Strategy (ICAO MID Regional Office) — MID realisation; monitored by MIDANPIRG.