Aeronautical administrative messages (priority indicator KK) comprise messages regarding the operation or maintenance of facilities, the functioning of aeronautical telecommunication services and those exchanged between civil aviation authorities relating to aeronautical services. OpenLDI (Open LVDS Display Interface) is a high-bandwidth digital-video interface standard for connecting graphics/video processors to flat panel LCD monitors. Even though the promoter’s group originally designed it for the desktop computer to monitor application, the majority of applications today are industrial display connections. For example, displays in medical imaging, machine vision, and construction equipment use the OpenLDI chipsets. Service messages (priority indicator as appropriate). This category comprises messages originated by aeronautical fixed stations to obtain information or verification concerning other messages which appear to have been transmitted incorrectly by the aeronautical fixed service.

Aeronautical information services (AIS) messages (priority indicator GG) comprise messages concerning NOTAMs and SNOWTAMs.Messages requesting information take the same priority indicator as the category of message being requested except where a higher priority is warranted for flight safety. the three-letter designator identifying the organization (as seen in ICAO Doc 8585). If no such designator is allocated, YYY is used (YXY for military organizations). For aircraft in flight, ZZZ is used. Distress messages (priority indicator SS). This message category comprises messages sent by aircraft reporting that they are threatened by imminent danger and all other messages relative to the immediate assistance.

Flight regularity messages (priority indicator GG) comprise e.g. messages concerning aircraft servicing, non-routine landings, aircraft arrival or departure, parts and materials urgently required for the operation of aircraft, etc. NAN (next authority notified) - notifies the accepting unit that it can initiate a CPDLC start request.OpenLDI is based on the FPD-Link specification, which was the de facto standard for transferring graphics and video data through notebook computer hinges since the late 1990s. Both OpenLDI and FPD-Link use low-voltage differential signaling (LVDS) as the physical layer signaling, and the three terms have mistakenly been used synonymously. (FPD-Link and OpenLDI are largely compatible, beyond the physical-layer; specifying the same serial data-streams). MAC (message for abrogation of coordination) - indicates that a previous coordination or notification is being abrogated. 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. Automation of routine actions (information exchange) which allows the controllers to focus on more complex tasks (e.g. conflict detection and resolution) The SGI 1600SW was the only monitor produced in significant quantities with an OpenLDI connection, though it had minor differences from the final published standards. The 1600SW used a 36-pin MDR36 male connector with a pinout that differs from that of the 36-pin centronics-style connector in the OpenLDI standard.

REV (revision message) - replaces the verbal revision in case the accepting unit does not change as a result of the modification. ROF (request on frequency) - indicates a request by the accepting unit for an early transfer of the flight. RAP (referred activate proposal) - used by the transferring controller to propose non-standard transfer conditions. 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. OLDI is considered as one of the major enablers of the Single European Sky (SES). As required by Regulation 1032/2006 it shall be in use from 2009 by all ATC units providing service to general air traffic, and the reliability of every OLDI link shall be at least 99.86 %. This is equivalent to a down-time of not more than 12 hours per year (based on 24-hour availability). BenefitsRRV (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. The following categories are accepted for transmission by the aeronautical telecommunication service: Several AFTN communication centres, when connected to each other, form a network of fixed aeronautical telecommunication lines through which every AFTN station can be reached. Sometimes AFTN stations are connected to more than one centre or to other stations.