DATA TECH LOG LINKED IN In the first of a two-part series, we look at the increasing demand for efficiency – and find out what CPDLC is all about By Captain Jeremy Feldman, Log Board member ALL DATA LINK-EQUIPPED AIRCRAFT (CPDLC ATN VDL MODE 2) ARE REQUESTED TO LOG ON” How many of us have read this NOTAM in the past few years and simply shrugged, “What, that one again? That’s always there. Something to do with CPDLC.” The fact is, Controller Pilot Data Link Communications (CPDLC) is becoming more commonplace. For those still in the dark, here you can read some information on exactly what CPDLC is and how it works. What is CPDLC? Airspace is becoming more and more busy; air traffic demand is increasing, as is the demand for ever-greater efficiency. One of the principal limiting factors of operating in a busy airspace environment is that we use voice communications. A controller can only talk to one aircraft at a time, and the sector capacity is limited by the number of controllers and frequencies available. As early as 1983, the International Civil Aviation Organisation (ICAO) looked into the feasibility of a data link method of communication between pilots and air traffic controllers (ATCOs). The idea was to reduce the controllers’ workload, increase airspace capacity and improve operational safety. Data link was not a new concept; ARINC had introduced the Aircraft Communications Addressing and Reporting System (ACARS) in 1978, though airlines didn’t really start using it until the mid-1980s. Although useful for some inflight communications between an aircraft and airline, ACARS wasn’t capable of being a secure and reliable communications method between aircraft and ATCO. ICAO set up a committee to consider a concept called Future Air Navigation System (FANS), which sought to establish a strategy for future operational concepts for air traffic management (ATM) and, more specifically, data link. The committee’s report was published in 1988 and, in 1991, it formally defined the concept of – and requirements for – CPDLC and Automatic Dependant Surveillance (ADS). At the time, the most pressing need for a FANS data-link technology solution was on long-haul aircraft, where oceanic and remote airspace communications were limited to high frequency (HF) and satellite communications (SATCOM). Air-to-ground communications were – and in some cases still are – notoriously poor. Reception quality can be very degraded and establishing initial communications can be temperamental. This makes communicating effectively and clearly a challenge at the best of times. Boeing went on to develop a technology concept called FANS–1, which used the existing Inmarsat Data-2 service to deliver aircraft-to-ground data link communications using ACARS channels. This was later incorporated into the 747- 400 aircraft. Around the same time, Airbus developed FANS-A for its A330 and A340 aircraft. These were subsequently combined and evolved into FANS-1/A+. Although work was under way for long-haul aircraft using HF and SATCOM, the demand for long- and short-haul aircraft using very high frequency (VHF) was evident. Generally speaking, continental airspace had a more comprehensive VHF network, so the next focus was to develop pilot-to-ATCO data link using VHF networks. One of the problems of developing data link methods over VHF was that data- transfer speeds were slow and unreliable. There was also a lack of ATM ground- based architecture to support a data link network. In 1996, ICAO adopted and standardised the VHF digital link (VDL) Mode 2. This provided a protocol to enable transfer of data up to 31.5kbps, which was greater than before, and used differential 8-phase shift keying. This allowed for a more reliable and secure data transfer protocol. VDL Mode 2 was used by Eurocontrol to develop a data link platform, later commonly known as Link 2000+ (also FANS-2). ICAO also used VDL Mode 2 to develop a data link platform specifically for continental airspace, which has since come to be known as Aeronautical Telecommunication Network Baseline 1 (ATN-B1), or CPDLC. CPDLC specifically refers to data link using ATN-B1, but many air navigation service providers (ANSPs) commonly refer to Link 2000+/ FANS-2 and ATN-B1 as CPDLC. Setting standards In short, the global data link standard was set, and data link has become commonly known as CPDLC. The next stage was to get ANSPs and aircraft operators to implement and use the technology. In 2009, the European Commission published Regulation 29/2009 – Data link services for the Single European Sky, which included the Data Link Services Implementing Rule (DLS-IR). This is legally binding on aircraft operators and ANSPs, and mandates a timeframe for certain data link services to be implemented. This was originally 5th February 2015, but because of technical connection problems, the date was pushed back to 5th February 2018 for ANSPs, and 5th February 2020 for aircraft operators, within European airspace. The global implementation of CPDLC is under way, and can be found in ICAO Provisions: Annex 10 Volume III Part I Chapter 3. CPDLC and data link is here to stay. As technology improves and demand increases, its use will become more common as we shift from voice communications. But how do we, as pilots, use CPDLC – and what can it do for us? What are the advantages and – more importantly – the risks? In a future edition of The Log we’ll look at the functions of CPDLC services and how they work for pilots and ATCOs. Communication satellites VHF remote ground station Ground earth station Air traffic service unit (ATSU) Data link services provider (DPS)