Future Air Navigation Systems (FANS) — Page 322, Lesson 380

I want to walk you through the Future Air Navigation Systems — FANS — and I’ll start with the physical pieces you’ll actually see and touch in the cockpit, because that’s how the whole data link story begins. First, the VISUAL. That’s the “Attention Getter” — light and sound. Its job is simple but critical: it alerts the pilot that an incoming data link message has arrived. Think of it as the cockpit’s way of saying “look here, something needs your attention.” It’s the sensory cue that pulls your eyes to the screen. Next, the PRINTER. That gives you a hard copy output — a physical printout of the message. So you have two ways to get the information: the visual/sound alert to catch your attention, and the printer to give you a permanent paper record. Now, the heart of this system is ACARS — the Aircraft Communication Addressing and Reporting System. Let me unpack that name, because it tells you what it does. It’s an addressing system — each message is addressed to a specific aircraft or ground station — and it’s a reporting system, because aircraft use it to send reports. ACARS uses data link format to pass messages between the aircraft and ATC — Air Traffic Control — or between the aircraft and the aircraft operating companies. The physical medium is VHF — Very High Frequency radio. And the messages can be printed out in the cockpit, which is where that printer comes in. Here’s the historical progression, and it matters because it explains why the system covers the whole globe. In the early 1990s, this service was extended to SATCOM — satellite communications — for flights outside VHF coverage, using geostationary satellites. Geostationary means the satellite stays fixed over one spot on the equator, so it can cover a large region continuously. But there was still a gap — the polar regions. That gap was closed in 2001 by extending the service to HF — High Frequency radio. Now, in the 1990s, something important happened: interfaces with the FMS — the Flight Management System — were developed. This allowed operational data to be evaluated using the FMS. What kind of data? For example, meteorological information — weather — and alternate flight plan routes. So instead of just passing text messages, the system could feed real operational data into the flight management computer for evaluation. Maintenance functions were also added, allowing independent monitoring of the aircraft systems — the aircraft could watch its own systems and report on them. This whole implementation is done through the ATSU/DCDU — the Air Traffic Service Unit and the Data link Cockpit Display Unit. The DCDU is the screen in the cockpit where you see and interact with the data link messages. The ATSU is the ground-side service unit. Let me clarify a small naming point. The excerpt writes “ATSU” but then spells out the full name as “ATCSU” — the Air Traffic Service Unit. Same unit, just a slight abbreviation variation in the text. The ATSU is able to provide the following services to aircraft: Flight Information Service, Alerting Service, Air Traffic Advisory Service, and Air Traffic Control Service. And that Air Traffic Control Service itself breaks down into three phases: Area, Approach, and Aerodrome. So Area control handles en-route traffic, Approach handles arrivals and departures near the airport, and Aerodrome handles the traffic in the immediate airport environment. Finally, the big-picture framework: CNS/ATM — Communications, Navigation and Surveillance Systems, and Air Traffic Management. CNS/ATM is designed to use various levels of automation, digital technology, and satellite systems to give a Seamless Global Air Traffic Management System. “Seamless” is the key word — no gaps, no boundaries, one continuous global system. And here’s the crucial distinction you must keep straight: Communications, Navigation and Surveillance Systems refer to the facilities offered by an ATSU — that’s the air traffic service provider. Air Traffic Management refers to the facilities offered by an Aircraft Operational Centre — the AOC. That’s basically the airline, or company, operating the aircraft. So CNS is the ATC side, ATM is the airline side. Two different providers, two different sets of facilities, one seamless global system. So the whole picture: ACARS moves the messages over VHF, SATCOM, and HF; the visual and printer get your attention and give you a record; the FMS interface lets you evaluate operational data; and CNS/ATM ties it all into a seamless global air traffic management system.