Right at the top, you see 121.5 MHz listed with a page reference of 115 — Page 163, Lesson 142

This is the index of your Communications textbook. I want to walk you through what it tells us about the structure of the course and the key topics we'll be covering. Right at the top, you see 121.5 MHz listed with a page reference of 115. That's the international aeronautical emergency frequency — the one you monitor when you're in trouble or when you want to hear if anyone else is. We'll get to it in detail later. Then we have a long list of abbreviations and terms. Let me highlight the ones that are fundamental to your training. ACARS — that's the Aircraft Communications Addressing and Reporting System. It's a digital data link system that lets the aircraft exchange messages with ground stations automatically. ACAS — the Airborne Collision Avoidance System. That's the system that warns you of conflicting traffic and gives you resolution advisories. ACC — Area Control Centre. That's the air traffic control facility that handles aircraft en route, between departure and arrival. ADF — Automatic Direction Finder. That's a radio navigation aid that points to a non-directional beacon. ADR — that could be Air Data Reference, part of the air data system. Aerodrome Control Service — that's the air traffic control service for aerodrome traffic, so the tower at an airport. Aeronautical Mobile Service — that's the radio communication service between aircraft stations and ground stations, or between aircraft stations themselves. Aeronautical Station — that's a ground station in the aeronautical mobile service. So the transmitter on the ground that talks to aircraft. AFIS — Aerodrome Flight Information Service. That's a service that provides information to aircraft in the vicinity of an aerodrome, but without the full control authority of a tower. AFTN — Aeronautical Fixed Telecommunication Network. That's the global network for exchanging flight plans, weather, and other operational messages between fixed ground stations. AIP — Aeronautical Information Publication. That's the official publication from each state containing all the permanent aeronautical information you need for flight planning. AIRAC — Aeronautical Information Regulation and Control. That's the system that ensures changes to aeronautical information are published on common effective dates, so you know when to expect updates. Air-ground Communication — that's two-way communication between aircraft and ground stations. Air Traffic Service — that's the umbrella term for all the services that help aircraft fly safely and efficiently: air traffic control, flight information, and alerting. Air Traffic Services Unit — that's any unit providing air traffic services, like a control tower or an area control centre. Airway — that's a defined corridor in the sky, usually 10 nautical miles wide, along which aircraft are routed. All Stations — that's a call meaning "everyone listening on this frequency." Altitude — that's vertical distance above mean sea level. Approach Control Service — that's the air traffic control service for arriving and departing aircraft, usually within about 30 to 50 nautical miles of the airport. Apron — that's the area of an airport where aircraft are parked, loaded, unloaded, or refuelled. Area Control Centre — that's the same as ACC, the facility that controls aircraft en route. ATIS — Automatic Terminal Information Service. That's a continuous broadcast of recorded aeronautical information at an airport, like weather, runways in use, and NOTAMs. You'll listen to it before you contact the controller. ATS — Air Traffic Services. That's the same as Air Traffic Service. ATSU — Air Traffic Services Unit. That's the same as ATSU. Now, the index also shows page numbers. For example, Abbreviations appears on pages 9 and 14. Aeronautical Station appears on pages 6 and 60. So you can see that some terms are introduced early and then revisited in more depth later. This index is your roadmap. When you're studying and you need to find a specific term or concept, you come here first. It tells you exactly where in the book to look. Let's move on to the next excerpt.