Future Air Navigation Systems (FANS) — Page 330, Lesson 388

Right, let's get into the Future Air Navigation Systems chapter. This is the FANS concept, and I want to start by clearing up a common point of confusion right at the top. An ATSU — that's an Air Traffic Service Unit, the ground facility that talks to you — can use a combination of data link services. Now, there are three main services in play here: AFN, ADS, and CPDLC. Let me define each one properly. AFN is the Air Traffic Facilities Notification. It's the FANS service that tells the ground system you're there and establishes the connection. ADS is Automatic Dependent Surveillance — the aircraft automatically transmits its position and other data to the ground. And CPDLC is Controller-Pilot Data Link Communications — the text-based messaging between you and the controller. Now here's the critical architecture rule. An ATSU may use AFN only, or ADS only, or CPDLC only. Or it may combine AFN with CPDLC, or ADS with CPDLC. But — and this is the key limitation — it may not use AFN and ADS together. Those two are mutually exclusive in this architecture. So whenever you see a FANS setup, remember: CPDLC can pair with either, but AFN and ADS never pair with each other. The typical architecture is shown in the next diagram, Figure 24.4, and Figure 24.5 shows a typical DCDU message display — that's the Data Control and Display Unit, the screen where you'd see these CPDLC messages. Now let's move to FANS B. FANS B is very similar to FANS A, but it operates within High Density airspace having good VHF coverage. So the key difference is the environment — FANS B is for busy airspace where you have solid VHF radio coverage. FANS B is operated over the Aeronautical Telecommunications Network, the ATN, which is operated by SITA. Now, the ATN is an internetwork architecture — it allows ground/ground, ground/air, and avionic data subnetworks to interoperate. So it's the backbone that lets all these different data networks talk to each other. Figure 24.6 shows a typical ATN organization. Now, this chapter also gives us a useful abbreviations list, and I want to walk you through these because you'll see them constantly. Let me group them by function. Starting with communications. ATIS is the Automatic Terminal Information Service — the continuous broadcast of airport and weather information. D-ATIS is the Data Link version, the Data Link Air Terminal Information Service. HF is High Frequency, a portion of the RF spectrum. SATCOM is Satellite Communications. VHF is Very High Frequency, also a portion of the RF spectrum. Then we have the system-level abbreviations. FANS itself is the Future Air Navigation System. ACARS is the Aircraft Communications Addressing and Reporting System — the data link system for aircraft. ACMS is the Aircraft Condition Monitoring System. ADS is Automatic Dependent Surveillance, and ADS-C is Automatic Dependent Surveillance - Contract, specifically for FANS 1/A. AFN is the Air Traffic Facilities Notification for FANS. Now some security and networking terms. AMS is ACARS Message Security, as specified in ARINC 823. AOA is ACARS Over AVLC. AOC is Airline Operational Communication, or the Airline Operational Centre. ARINC is Air Radio Incorporated, the USA-based standards body. ATM is Air Traffic Management. ATN is the Aeronautical Telecommunications Network — note the book lists it as France, which is a bit of a quirk, but that's what's given. ATSU is the Air Traffic Service Unit. AVLC is Aviation VHF Link Control. CDU is the Control and Display Unit. CMF is the Communications Management Function. And CMU is the Communications Management Unit. So when you put this together: the CMU is the hardware, the CMF is the function that manages communications, and the CDU is how you interact with it. These are the building blocks of the FANS environment you'll be operating in. That's the foundation of FANS — the service combinations, the FANS B environment over the ATN, and the key abbreviations. Let's continue when you're ready.