Now the altimetry settings — Page 661, Lesson 789

This is the index of the book — the map of the entire Instrumentation syllabus. I want to walk you through the entries that appear here, because each one is a technical term you will meet in the chapters ahead, and I want you to see how they group together. Let's start with the pressure terms. PSI stands for pounds per square inch — that's a unit of pressure, and you'll meet it on page 42. Then there's PUDSOD on page 46 — that's an acronym, and I'll define it properly when we reach that page. Pure Frequency appears on page 255, which relates to how we describe signals in the navigation instruments. Now the altimetry settings. QFE and QNH both appear on page 64. QFE is the pressure setting that makes the altimeter read zero at a given airfield elevation — it gives you height above the field. QNH is the setting that makes the altimeter read elevation above mean sea level when you're on the ground. These are the two fundamental pressure references you'll set on the altimeter sub-scale. Moving to the R section, which is rich. RA on page 483 is the abbreviation for Radio Altimeter — that's the instrument that measures your actual height above the terrain below, using radio waves reflected from the ground. The full term Radio Altimeter appears at pages 263, 348, and 380, and Radio Altitude — the height value it produces — is on page 285. RAAS on page 471 is the Runway Awareness and Advisory System — that's a warning system that alerts the crew about runway proximity and status. RAM on page 309 is Random Access Memory — the computer memory that can be read from and written to freely. The full term is spelled out as Random Access Memory (RAM) on the same page. And ROM at the end of this excerpt is Read Only Memory — memory that can only be read, not written to, and it's listed as Read Only Memory (ROM). Now the temperature and air data terms. RAT on page 31 is Ram Air Temperature — that's the temperature of the air as it's compressed and heated when it rams into the aircraft's sensor at speed. The full term Ram Air Temperature (RAT) appears on pages 30 and 31. Ram Rise on page 31 is the temperature increase caused by that compression of the air — the difference between the static air temperature and the ram air temperature. Then we have some gyroscopic instruments. Rate Gyro on pages 144 and 185 measures the rate of rotation about an axis. Rate-integrating Gyro on page 233 goes further — it integrates that rate to give a displacement. Rate of Turn Indicator on page 185 shows how fast the aircraft is turning. Rate Sensors on page 253 are the devices that detect these rates. And Rate of Climb and Descent Indicator (RCDI) on page 73 is the vertical speed indicator — it shows how quickly you're climbing or descending. There are some mechanical terms too. Ranging Arm on page 85 and Ratio Arm on page 85 — these are parts of a mechanical computer mechanism, likely in the air data computer. 'Rams' Horns' on page 215 — that's a descriptive name for a control yoke shape, the steering wheel of the aircraft. Random Wander on pages 142, 156, and 157 — that's an error characteristic of gyroscopes, where the instrument drifts unpredictably over time. Rapid Synchronisation on page 213 — that's the fast process of aligning a gyro or compass to its correct reading. RANGE on page 286 — that's a display mode, likely on a weather radar or navigation display, showing distance from the aircraft. Raw Information on page 342 — that's unprocessed data presented directly to the pilot, before any computer interpretation. And Readability on page 8 — that's a quality of instrument displays, how clearly the information can be read. So you can see the structure of this book: pressure units, altimeter settings, radio altimetry, computer memory, temperature probes, gyroscopic instruments, and display concepts. Each of these will be defined fully in its chapter. For now, just know these are the landmarks — the terms you'll be tested on.