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. NAN (next authority notified) - notifies the accepting unit that it can initiate a CPDLC start request. 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.

REV (revision message) - replaces the verbal revision in case the accepting unit does not change as a result of the modification. 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. 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).

Definition

Urgency messages (priority indicator DD). This category comprises messages concerning the safety of a ship, aircraft or other vehicles, or of some person on board or within sight. The following categories are accepted for transmission by the aeronautical telecommunication service: 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. 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. MAC (message for abrogation of coordination) - indicates that a previous coordination or notification is being abrogated.

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. MAS (manual assumption) - informs the transferring unit that the accepting unit has established radio communication with the flight. Aeronautical information services (AIS) messages (priority indicator GG) comprise messages concerning NOTAMs and SNOWTAMs. Automation of routine actions (information exchange) which allows the controllers to focus on more complex tasks (e.g. conflict detection and resolution)

Benefits

CDN (coordination message) - sent by the accepting controller as a proposed modification or as a counter-proposal. 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. Meteorological messages (priority indicator GG) comprise messages concerning forecasts (TAFs) and observations and reports (METAR, SPECI). 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). Benefits 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.

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. TIM (transfer initiation message) - signifies the end of the coordination pjase and the start of the transfer phase. At the majority of aerodromes where ATS is provided, there is an AFTN station. A number of such stations grouped together and around an AFTN centre form an AFTN circuit. The OpenLDI standard was promoted by National Semiconductor, Texas Instruments, Silicon Graphics (SGI) and others. OpenLDI wasn't used in many of the intended applications after losing the computer-to-monitor interconnect application to a competing standard, Digital Visual Interface (DVI). [1]A worldwide system of aeronautical fixed circuits provided, as part of the aeronautical fixed service, for the exchange of messages and/or digital data between aeronautical fixed stations having the same or compatible communications characteristics. 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. 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. Flight safety messages (priority indicator FF) comprise movement and control messages (e.g. FPL, DLA, CNL, DEP, ARR, OLDI messages, etc.), messages by the operator that are of immediate concern to aircraft and some meteorological messages (SIGMET, special air-reports, AIRMET, volcanic ash and tropical cyclone advisories).