Description

On-Line Data Interchange (OLDI) is a protocol for co-ordination and transfer of current flight data between adjacent air traffic control units. Its development started in the 1990s in Europe.

The main objective of applying OLDI for ATC purposes is:

• to automate co-ordination and flight data information exchange between ATC units
• to ensure timely delivery of standard messages

In order to facilitate implementation, common rules and message formats were elaborated and agreed by the agencies concerned.

OLDI is considered as one of the major enablers of the Single European Sky (SES). As required by Regulation 2023/1771 it must be used by all area control units within the ICAO EUR region to support the coordination of transfer of control. The following processes are specified as mandatory and described in detail in Regulation 2023/1771:

• Notification (ABI message)
• Initial coordination (ACT message)
• Revision of coordination (REV message)
• Abrogaion of coordination (MAC message)
• Basic flight data (BFD message)
• Change to basic flight data (CFD message)

Provisions for the following processes are described in case the ATS units agree to conduct pre-departure notification, change-of-frequency or manual-assumption-of-communication:

• Pre-departure notification and coordination (CRQ and CRP messages)
• Change of frequency (COF message)
• Manual assumption of communications (MAS message)
• Crossing intention notification (XIN message)
• Crossing clearance request (XRQ message)
• Crossing counter-proposal (XAP message)
• Crossing cancellation (XCM message)

When CPDLC is used by the area control units, the following processes are to be supported by OLDI:

• Logon forward (LOF message)
• Next authority notified (NAN message)

Benefits

• Automation of routine actions (information exchange) which allows the controllers to focus on more complex tasks (e.g. conflict detection and resolution)
• Reduced controller workload due to reduced need for verbal coordination
• Better situational awareness
• Indirect improvement of ATS system safety features (e.g. MTCD)

Transaction Times

In order to ensure timely and effective exchange of messages, the following maximum transaction times are defined:

• 4 sec for 90% of transmitted/received messages
• 10 sec for 99.98 of transmitted/received messages

If no acknowledgement has been received within the specified time after transmission, a message is to be considered unsuccessfully transmitted or processed and a warning is to be displayed.

OLDI Messages

Note: The list below contains the most frequently used OLDI messages and the explanations are intended to provide the basic meaning of those messages rather than being a complete description. The OLDI specificcation can be found in the Further Reading section.

• Basic messages
  • ABI (advanced boundary message) - notifies the next ATC unit of the flight and facilitates early correlation of radar tracks.
  • ACT (activate message) - replaces the verbal estimate.
  • REV (revision message) - replaces the verbal revision in case the accepting unit does not change as a result of the modification.
  • PAC (preliminary activate message) - notifies the next ATC unit of a flight that has not departed yet in situations where the flight time from departure to the boundary is less than the requirement for an ACT message.
  • MAC (message for abrogation of coordination) - indicates that a previous coordination or notification is being abrogated.
  • LAM (logical acknowledgement message) - informs the sending ATC unit's FDPS of an OLDI message reception.
• Ground-ground situational awareness
  • BFD (basic flight data) - forwards basic flight data to an ATSU whose airspace is not planned to be penetrated by the flight but the route takes the flight close to the boundary.
  • CFD (change to flight data) - notification of significant changes to flight data previously sent with a BFD/CFD.
  • TFD (terminate flight data) - informs the receiving unit about the termination of the flight plan or route segment within the airspace of the sending unit.
• Civil-Military coordination
  • XIN (crossing intention) - informs the other unit of the intention to cross their airspace.
  • XRQ (crossing request) - forwards a request to cross the other unit's airspace.
  • XAP (crossing alternate proposal message) - transmits a counter-proposal for airspace crossing.
  • XCM (crossing cancellation message) - informs the addressed unit that a previous notification or coordination is being abrogated.
  • ACP (acceptance message) - indicates agreement to a crossing request or counter-proposal.
  • RJC (reject coordination message) - indicates rejection to a crossing request or counter-proposal.
  • SBY (standby message) - acknowledges the receipt of a message proposing transfer conditions and indicates that the proposal is being referred to the controller for a decision.
• Pre-departure coordination
  • CRQ (clearance request message) - used to request departure clearance from an aerodrome control to the next ATSU on the route of flight.
  • CRP (clearance response message) - used to issue of departure clearance data from an ACC to an aerodrome/approach control unit.
• Coordination (dialogue procedure). This procedure provides facilities for communication and negotiation between controllers in the coordination phase and for communication in the transfer phase. The ACT and REV messages described above may also be used for this procedure.
  • RAP (referred activate proposal) - used by the transferring controller to propose non-standard transfer conditions.
  • RRV (referrred revision proposal) - used by the transferring controller to propose non-standard revisions.
  • CDN (coordination message) - sent by the accepting controller as a proposed modification or as a counter-proposal.
  • RRQ (release request) - used by the accepting unit to request the release of a flight.
  • RLS (release) - used by the transferring unit to release a flight. The message may be used as a response to a RRQ or on the initiative of the transferring controller.
  • RTI (request tactical instructions) - used by the accepting unit to request the transfer of a flight on an assigned heading, speed, rate of climb or descent or on a direct routing.
  • TIP (tactical instructions proposal) - used by the transferring unit to coordinate the transfer of a flight on an assigned heading, speed, rate of climb or descent or on a direct routing.
• Transfer of communication
  • ROF (request on frequency) - indicates a request by the accepting unit for an early transfer of the flight.
  • COF (change on frequency) - indicates that a flight has been instructed to contact the accepting sector.
  • MAS (manual assumption) - informs the transferring unit that the accepting unit has established radio communication with the flight.
  • TIM (transfer initiation message) - signifies the end of the coordination pjase and the start of the transfer phase.
  • HOP (handover proposal) - proposes the flight for handover.
  • SDM (supplementary data message) - transmits control data and changes thereto from the transferring unit to the accepting unit. Can be used by the accepting unit to notify the transferring unit of the frequency to which the flight is to be transferred.
• Controller Pilot Data Link Communications (CPDLC) support
  • LOF (logon forward) - provides ATN logon parameters to the receiving unit.
  • NAN (next authority notified) - notifies the accepting unit that it can initiate a CPDLC start request.

The messages to be used and certain parameters thereof are defined in bilateral agreements between the particular ATC units.

Related Articles

• Regulation 2023/1771 amending Regulation 2017/373 as regards ATM and ANS systems

Further Reading

• OLDI Specification Edition 5.1, EUROCONTROL, 2023
• OLDI data exchange implementation report 2017