The Essentials of Datalink Communications The origins and course of Air-to-Ground Messaging The Essentials of Datalink Communications Contents international Trip Support | international Trip The Technology that HR Created 02 Inmarsat Satellite 06 Growing into an Operational Necessity 03 Iridium Satellite 07 UAS Communications Mechanisms 04 Upcoming Regulations 10 VHF Radio 05 The Future of ACARS 11 © Copyright 2016 Page 1/12 The Technology that HR Created t one time in the not-so-distant past, pilots and other ARINC’s solution was an automated system, called the A flight crew members were paid different rates for the ARINC Communications Addressing and Reporting System, time they were airborne versus the time they were performing or ACARS for short, which sent short text data from the ground operations. Events like aircraft pushback, taxi, takeoff, avionics of the aircraft directly to the ground-based entities landing, and gate arrival were transmitted via voice over radio through Very High Frequency (VHF) radio frequencies frequencies to operators who would relay this information back without any crewmember involvement. The aircraft was to the airlines. The pilots were responsible for self-reporting programmed to take advantage of switches and automation their own times and movements. Understanding that people points on the aircraft, resulting in the creation of a set of can sometimes be forgetful, or worse, willfully manipulative, messages referred to as the OOOI report. An OOOI report is the major airlines began searching for a solution that tracked any of four messages: Out, Off, On and In. Still in wide-scale crewmember pay in a more structured and accurate way. use today, the OOOI report is any one of four messages Since time card machines weren’t an option for the flight generated by specific events on the aircraft. deck, they reached out to communication and engineering company ARINC for help with a solution. The events are: Out: Off: The precise time when The precise time when the aircraft is “pushed the aircraft takes off from back” from the gate, or the runway, normally in other words, “out” determined by a of the gate, normally “weight on wheels” determined by discreet sensor built into the door sensors aircraft’s undercarriage On: The precise time when In: the aircraft touches The precise time when the down on the runway, aircraft arrives at the gate, normally determined normally determined by the by the same same discreet door sensor “weight on used in the Out message wheels” sensor built into the aircraft’s undercarriage he concept of the OOOI message took hold quickly, and term ACARS remains in use, but most people in the aviation The Essentials of Datalink Communications T many of the airlines paid to have VHF ground stations industry simply refer to it as “datalink.” installed at the busiest airports. Over the next few years, further applications were developed that took advantage of The datalink system that was started to track crewmember the ACARS protocol and other providers began to emerge hours for payroll purposes in the late 1970s continued to with the ability to provide ACARS services, the most notable develop over the next 40 years, increasing its ability and of which being the French company, SITA, a leading provider service footprint. What was once limited to line-of-sight of international communication services for aviation. VHF towers at major airports, is now widely available in international Trip Support | international Trip most locations. UAS Free-text messaging, flight plan uplinks, text weather, and position reports started to become commonplace. At some This technical white paper will briefly review the evolution and point after the initial launch, the acronym ACARS was officially fundamentals of datalink, the system that was truly created in changed to the Aircraft Communications Addressing and response to a Human Resources problem, including its role in Reporting System, removing the reference to ARINC. The the modern-day flight operation and plans for its future. © Copyright 2016 Page 2/12 Growing into an Operational Necessity he OOOI message continues to this day to be one of the Soon, Air Navigation Service Providers (ANSPs) and Air T key features in the datalink service offering. However, Traffic Control (ATC) facilities around the globe started seeing shortly after the OOOI message was created, other message the benefit of voice-free communications. The accuracy sets were developed to take advantage of this new static- and efficiency of AOC/AAC messages was needed in other free text transmission method. Flight crews and dispatch critical messaging areas, like to issue clearances, diversions, offices quickly became enamored with the ability to type out position reporting, and other ATC functions. A new message a message on a keypad or keyboard instead of trying to relay set, called Air Traffic Control (ATC) or Air Traffic Services (ATS) messages via voice on congested, noisy, and fatiguing voice messages was created. The most prominent example of ATS radio transmissions. The new messages quickly improved messages was coined under the term Future Air Navigation accuracy, safety, and situational awareness. System (FANS). FANS messages are the current standard of safety of flight messages being transmitted over datalink. The set of messages developed shortly after the OOOI messages became known as Airline Operational Control FANS comes in many shapes and sizes, but the messages (AOC) and Airline Administrative Control (AAC) messages. typically consist of two main components: AOC and AAC messages are unprotected, meaning they are not regulated by any operational authority other than to the • Automatic Dependent Surveillance (ADS), which extent necessary to comply with the technical specification provides three-dimensional position data to ANSP for message creation. For example, the message formats and ATC agencies on the ground. ADS relays aircraft themselves were designed to flow properly through the location, speed, and altitude and supplements ACARS infrastructure, but the content of the messages is traditional radio position reports and radar data. ADS free-text or formatted text. technologies come in a few different “flavors,” but the datalink implementation is ADS-Contract (ADS-C), In addition to the OOOI reports, a number of AOC/AAC where the ATC host computer establishes a contract message sets were created and are still in use today, with the aircraft to report data at certain intervals including the following examples: • Controller-Pilot Datalink Communications (CPDLC), • Incremental Position Reporting and Estimated Time of which provides a two-way ATC communications Arrival (ETA) Messages between the flight crew and the ATC facility, reducing • Text Weather (METARs/TAFs/NOTAMs/PIREPs) the use of traditional radiology. which is prone to error • Graphical Weather Charts and lacks efficiency. • Pre-Departure Clearance (PDC) and Datalink Clearance (DCL) Messages Unlike AOC and AAC messages, ATS messages are • Flight Plan Uplinks protected and therefore cannot be altered. All messages • Oceanic Clearance Delivery (OCD) are built on approved templates that use standard text • Terminal Weather Information for Pilots (TWIP) and nomenclature, and with ATS messages, no free- • Digital Airport Terminal Information System (D-ATIS) text messaging is available. If your request cannot be The Essentials of Datalink Communications • Gate Notifications accomplished using the library of available requests or • Fuel and Service Requests responses, you must revert to voice communications. • Free-Text Messages • Maintenance Reporting • Airframe Fatigue Reports • Aircraft Engine and Health Reports international Trip Support | international Trip • Aircraft Weight-and-Balance Load Sheets and Trim Sheets • Diversion Tracking UAS • Special Passenger Advice • Other Fault and Abnormal System Status Reporting © Copyright 2016 Page 3/12 Figure 1: Figure 2: Sample ATC Communications using Protected ATS Datalink. Sample Message using Unprotected AOC Free-Text. In this example, the crew requests a climb to FL430, and is In this example, the crew has received a free-text message told to “standby” momentarily, then granted permission to from their service provider, who is updating them on their climb to FL430. The crew reports leaving their current altitude handling arrangements and transportation. (FL410) and when they are level at the new altitude (FL430). Communications Ground-Based Mechanism #1 Mechanisms VHF Connection Type: Line of sight very high-frequency radio transmissions (Networks) Usable Range: Up to 220 nautical miles Service Area: Typically near airports and other highly traveled regions atalink messages can be transmitted via four distinct Speed of Data: 2.4 - 31.5 kbps networks. The first two, Very High Frequency (VHF) and D Relative Cost: Lowest High Frequency (HF), are ground-based radio mechanisms. The second two, Inmarsat and Iridium, are satellite-based technologies. Most business jets are configured in such a way that the Ground-Based Mechanism #2 The Essentials of Datalink Communications aircraft tries to communicate over VHF radio first, as it is the least expensive option, and if a VHF connection cannot be established, the aircraft will switch over and attempt to send the message over satellite. Even though aircraft can HF have both Inmarsat and Iridium antennas, which support Connection Type: Line of sight high-frequency a number of different functions, the aircraft can only