Then we move into the A section — Page 653, Lesson 749

This is the index of the book — the map of everything we're going to cover together. I want to walk you through what's here, because it tells you exactly what an ATPL-level instrumentation syllabus looks like, and it gives you the vocabulary you'll be using for the rest of your training. Let's start with the very first entry: 400 – 330 feet RA, pointing to page 382. RA means Radio Altimeter — that's the instrument that measures your actual height above the ground using radio waves, not barometric pressure. The range 400 to 330 feet is a specific band you'll see referenced in procedures, likely related to callouts or decision heights during approach. Then we move into the A section. Above Ground Level (AGL) — page 263 — that's your height measured from the terrain directly beneath you, as opposed to altitude above mean sea level. You'll see this constantly in navigation and performance. Absolute — page 33 — and Absolute Temperature — page 83. Absolute temperature is measured from absolute zero, in Kelvin. When you see "absolute" in instrumentation, it usually means a measurement taken from a true zero reference point, not a relative one. Now the acronyms start. ACARS — page 319 — that's the Aircraft Communications Addressing and Reporting System. It's the digital datalink that lets the aircraft send and receive text messages, weather, and flight plans with ground stations. ACAS — page 479 — the Airborne Collision Avoidance System, which is the traffic alerting system that warns you of conflicting aircraft. Acceleration — page 123 — and then a cluster of related entries: Acceleration and Turning Errors — page 123 — Acceleration Error — page 174 — and Acceleration Errors — pages 126 and 178. These are the errors you get in gyroscopic instruments, like the attitude indicator and the compass, when the aircraft accelerates or turns. The distinction between the singular and plural entries tells you these errors appear in multiple contexts across the book. Accelerometer — page 228 — and Accelerometers — page 229. An accelerometer measures acceleration forces along an axis. You'll find these in inertial navigation systems and in the ADI, the Attitude Director Indicator. Accumulator — page 308 — that's a hydraulic or pneumatic storage device that holds fluid or gas under pressure for later use. Active Waypoint — page 293 — that's the current navigation point the flight management system is steering you toward. ADC — pages 91, 97, 271, and 294 — that's the Air Data Computer. This is a big one. The ADC takes raw pressure and temperature inputs and computes things like altitude, airspeed, and Mach number. It appears in multiple chapters because it's central to so many systems. Additional Parameters — page 500 — and ADI — pages 281 and 285 — the Attitude Director Indicator, which is the primary flight display showing pitch and roll attitude, with flight director commands overlaid. Adiabatic Heating — page 30 — that's the temperature change that happens when air is compressed or expanded without heat being added or removed. You'll see this in the pitot-static system, where ram air compression heats up. Adjustable Aeroplane Datum — page 178 — and Adjustable Index — page 85 — these are calibration references. A datum is a fixed reference point, and an adjustable index is a movable marker you set on an instrument, like a barometric pressure setting on an altimeter. ADS — pages 97 and 327 — and then the book spells it out for you: ADS: Automatic Dependent Surveillance — page 326. This is the surveillance system where the aircraft automatically broadcasts its position, derived from onboard navigation, to ground stations or other aircraft. "Automatic" means no pilot action, "Dependent" means it relies on the aircraft's own navigation data. Advantages of an Air Data System — page 100 — that's the section covering why we centralize air data computation. Advisories — page 433 — those are non-critical alerts, informational messages rather than warnings. Aerodrome — page 319 — that's the formal term for an airport, the defined area for aircraft operations. Finally, Aerodynamic Feedback — page 354 — that's when aerodynamic forces feed back into a control or instrument system, and Aeronautical Telecommunications Network (ATN) — that's the global digital network that connects aircraft, ground stations, and air traffic control for data communication. So this index is your roadmap. Every one of these terms — the ADI, the ADC, the accelerometers, the radio altimeter — we're going to meet in detail as we work through the chapters. Right now, I just want you to recognize the shape of the syllabus: it's about how we measure the air around us, how we measure our motion, how we navigate, and how we communicate that information to the pilot and to the ground. That's the whole of instrumentation in one paragraph.