EOBT – Estimated Off-Block Time

Estimated Off-Block Time (EOBT) is a fundamental timing milestone in aviation, representing the projected moment when an aircraft will begin departure movement from its parking position. This concept underpins modern airport, airline, and air traffic management processes and is tightly integrated with both day-of-operations procedures and regulatory compliance.

What is EOBT?

EOBT is defined by ICAO (International Civil Aviation Organization) as the estimated time an aircraft will start movement associated with departure from its parking position. This is the point where all pre-departure activities—boarding, fueling, catering, baggage loading, and technical checks—are complete, and the aircraft is ready for pushback or taxi.

EOBT is a mandatory entry in flight plans and is encoded in Item 18 under the DEP field. It forms the basis for coordination among airlines, airport operators, ground handlers, air navigation service providers (ANSPs), and the Network Manager (NM) for Air Traffic Flow Management (ATFM).

EOBT’s Role in Aviation Operations

• Departure Sequencing & Slot Allocation:
  EOBT acts as the temporal anchor for departure sequencing and allocation of take-off slots within ATFM systems. Its accuracy directly impacts predictability and efficiency, especially at busy airports and in congested airspace.

• Airport Collaborative Decision Making (A-CDM):
  In A-CDM environments, EOBT is monitored and updated continuously to reflect real-time operational status. It is the starting point for coordinated departure management, enabling all stakeholders to share a common view of readiness and resource needs.

• Regulatory Compliance & Network Coordination:
  EOBT must be kept accurate in line with ICAO Doc 4444 and regional procedures (e.g., EUROCONTROL in Europe). If operational changes cause a deviation of more than 15 minutes, EOBT must be amended via DLA (delay) or CHG (change) messages, ensuring synchronization with the Network Manager and avoiding penalties or loss of slots.

Related Departure Timing Concepts

Scheduled Off-Block Time (SOBT)

SOBT is the planned, published time an aircraft is scheduled to leave its stand, set during the airline’s scheduling process well in advance. SOBT is used for airport resource planning but is not updated in real time.

Target Off-Block Time (TOBT)

TOBT is a real-time estimate, updated locally by ground handlers or operators, indicating when the aircraft will actually be ready for departure. TOBT is used in A-CDM airports and must be kept accurate within a tighter window (often ±5 minutes).

Calculated Off-Block Time (COBT)

COBT is generated by ATFM or A-CDM systems and represents the optimal time for pushback, taking into account real-time airport and airspace conditions, ensuring compliance with network slot allocations.

Target Start-Up Approval Time (TSAT)

TSAT is the time assigned by ATC or the A-CDM system for when an aircraft can expect pushback or engine start approval, based on TOBT, COBT, and current runway/airspace status.

Calculated Take-Off Time (CTOT)

CTOT is the time allocated by ATFM for an aircraft to become airborne, factoring in sector demand and airspace constraints. It is binding within a set tolerance window, and failure to meet the CTOT can result in delays or slot loss.

Actual Off-Block Time (AOBT)

AOBT is the exact moment an aircraft physically leaves its parking position, recorded via ground systems or reported by flight crew. It is the definitive operational timestamp for performance measurement.

Actual Take-Off Time (ATOT)

ATOT is when the aircraft actually becomes airborne, as recorded by surveillance systems. It is used for post-flight analysis, billing, and regulatory reporting.

EOBT in A-CDM Workflows

In A-CDM, EOBT serves as a foundational milestone, with all subsequent times (TOBT, COBT, TSAT, CTOT) building upon it. As ground operations progress, if the real-time estimate (TOBT) deviates from EOBT by more than 15 minutes, an updated EOBT must be filed to ensure the network, airport, and all stakeholders remain synchronized.

Typical Workflow:

1. Flight Plan Filing: EOBT is entered based on expected readiness.
2. Real-Time Monitoring: Ground handlers track turnaround progress and update TOBT as needed.
3. EOBT Update: If TOBT shifts by >15 minutes, a DLA/CHG message is sent to update EOBT in the flight plan.
4. Coordination: Updated EOBT is shared with all stakeholders and reflected in DPI (Departure Planning Information) messages.
5. Network Alignment: The Network Manager recalculates slot allocations, COBT, and CTOT as necessary.

EOBT Update Procedures

• Continuous Monitoring:
  Airlines and ground handlers must monitor ground operations versus EOBT.
• Discrepancy Management:
  When TOBT is forecast to differ from EOBT by more than 15 minutes, update EOBT promptly.
• Submission Process:
  Use DLA or CHG messages via AFTN or digital systems to update EOBT in the central flight plan database.
• Stakeholder Notification:
  Ensure the updated EOBT is visible to crews, ATC, ground handling, and the Network Manager.

Automated systems at A-CDM airports can facilitate these updates and help maintain regulatory compliance.

Use Cases & Operational Scenarios

Routine Departure:
Flight SOBT and EOBT are both set for 12:00 UTC. Ground handling proceeds as planned, TOBT remains at 12:00, and actual pushback (AOBT) occurs at 12:03. No updates are needed; all times align and departure is punctual.

Delay Scenario:
EOBT is 14:00 UTC, but due to late catering, TOBT is updated to 14:25. Since the deviation exceeds 15 minutes, a DLA message is filed, network slot allocation is revised, and all stakeholders are informed. Departure proceeds on the new timeline.

Early Readiness:
EOBT is 10:45 UTC, but ground operations finish at 10:35. Since TOBT is earlier than EOBT, no auto-update occurs; the operator may file a CHG if earlier departure is possible.

Best Practices for EOBT Management

• Monitor and Update:
  Continuously compare TOBT with EOBT and update when necessary.
• Avoid “Gaming”:
  Do not file artificially early EOBTs to manipulate slot allocation.
• Leverage Automation:
  Use A-CDM tools and automated update services wherever possible.
• Communicate Proactively:
  Ensure all relevant parties are aware of changes as soon as they occur.
• Review Performance:
  Regularly assess punctuality, slot compliance, and the effectiveness of departure management processes.

Departure Milestone Times: Summary

References

• ICAO Doc 4444 – Procedures for Air Navigation Services – Air Traffic Management
• ICAO Doc 7030 – Regional Supplementary Procedures
• ICAO Annex 2 – Rules of the Air
• EUROCONTROL Network Operations Handbook
• IATA Worldwide Airport Slot Guidelines (WASG)
• EUROCONTROL A-CDM Implementation Manual
• EUROCONTROL EOBT Guidance
• Airport-CDM Implementation Resources

Conclusion

EOBT is a central concept in flight planning and airport operations, ensuring that departure timing is accurate, coordinated, and compliant with both local and network-level requirements. Its proper management underpins efficient use of resources, regulatory compliance, and high levels of punctuality in the global air transport system.

For airlines, airports, and air traffic managers, a robust understanding of EOBT and its integration into operational workflows is essential for achieving optimal performance and supporting the industry’s collaborative approach to capacity and efficiency challenges.