Avionics Study Guide

📖 Core Concepts Avionics – all electronic systems on an aircraft that provide communication, navigation, display, and management functions. Core functional areas – Communications: voice & data links between cockpit, ground, passengers. Navigation: satellite (GPS, WAAS, EGNOS), inertial, and ground‑based radio aids. Display & Management: glass‑cockpit screens that centralize flight data. Specialized systems: fuel monitoring, collision‑avoidance, weather detection, health‑monitoring. Glass cockpit – replacement of analog gauges with computer monitors that present a moving‑map and synthetic‑vision display. Fly‑by‑wire (FBW) – flight‑control surfaces are moved by electro‑actuators driven by computers rather than hydraulic cables. Data‑bus architecture – standardized digital networks (ARINC 429, 629, 664, 825, etc.) that let disparate avionics modules share data. Performance‑based navigation (PBN) – uses precise satellite navigation to meet defined lateral/vertical accuracy (e.g., LNAV/VNAV, RNP‑AR). --- 📌 Must Remember VHF voice band: 118.000 MHz – 136.975 MHz. Channel spacing: 8.33 kHz (Europe), 25 kHz (elsewhere). Modulation: Amplitude Modulation (AM), simplex. Power supplies: Light aircraft: 14 V or 28 V DC. Large airliners/combat jets: 115 V, 400 Hz AC. Key ARINC buses: ARINC 429 – medium‑speed, point‑to‑point. ARINC 629 – high‑speed, used on Boeing 777. ARINC 664 (AFDX) – Ethernet‑derived, commercial jets. ARINC 825 – CAN‑bus, on Boeing 787 / Airbus A350. ARINC 708 – weather radar interface. Collision‑avoidance: TCAS/TAAS – interrogates transponders, gives resolution advisories (RA). Simplified TAAS – passive, no RAs. Ground‑proximity vs terrain‑awareness: GPWS – radar‑altimeter, warns of imminent impact. TAWS – adds forward‑looking terrain mapping for predictive warnings. Fuel quantity indication – combines capacitance tubes, temperature sensors, densitometers, level sensors to compute fuel mass. --- 🔄 Key Processes Avionics Installation → Verification Ground test → Flight test → System alignment → Calibration. Position Computation (Integrated Display) GPS/WAAS → INS cross‑check → Ground‑based VOR/LORAN (if available) → Automatic update on moving‑map. Fuel Management Cycle Sensors → Fuel Quantity Indication System → Fuel Control & Monitoring System → Pump/valve commands → Balance CG & enable dump if required. TCAS Alert Sequence Interrogate nearby transponders → Compute closure rate → Issue Traffic Advisory (TA) → If conflict → Issue Resolution Advisory (RA). --- 🔍 Key Comparisons Analog gauges vs Glass cockpit Analog: mechanical needles, many separate instruments. Glass: digital screens, integrated moving‑map, reduced pilot workload. Fly‑by‑wire vs Hydraulic actuation FBW: electrical signals → actuators; includes flight‑control software safety checks. Hydraulic: fluid pressure → mechanical movement; heavier, no software layer. TCAS (TAAS) vs Simplified TAAS TCAS: active interrogation, provides resolution advisories. Simplified: passive listening, no RAs. ARINC 429 vs ARINC 629 429: 32‑bit, single‑sender, lower data rate. 629: 64‑bit, multiple‑sender, higher data rate, used on larger jets. --- ⚠️ Common Misunderstandings “VHF voice uses FM” – It actually uses AM (amplitude modulation). Inertial navigation needs GPS – INS works independently of external signals; GPS is used only for periodic updates. All modern jets have fly‑by‑wire – Some regional turboprops still use conventional hydraulic control. GPWS = full terrain awareness – GPWS only warns of imminent impact; TAWS provides predictive terrain alerts. --- 🧠 Mental Models / Intuition Avionics = Aircraft nervous system – sensors = nerves, processors = brain, displays = eyes. Data bus = circulatory system – ARINC lines transport “blood” (information) to every “organ” (subsystem). PBN = GPS‑guided highway – think of each approach as a “lane” with defined width (lateral) and height (vertical) tolerances. --- 🚩 Exceptions & Edge Cases Small GA aircraft may only have Simplified TAAS (no RAs). GPWS lacks forward‑looking terrain mapping – still vulnerable in mountainous terrain without TAWS. High‑frequency (HF) radio is required for oceanic flights where VHF coverage ends. Aircraft with 115 V/400 Hz AC need transformers/rectifiers for 28 V DC avionics; not all systems share the same voltage. --- 📍 When to Use Which Communication mode VHF → domestic, line‑of‑sight (< 300 NM). HF → trans‑oceanic, beyond VHF range. Satellite → global voice/data, especially over remote regions. Navigation source GPS/WAAS → primary for precision approaches. VOR/LORAN → backup or when GPS unavailable. Inertial → long‑duration, GPS‑denied environments (e.g., military). Data‑bus selection ARINC 429 → older or smaller aircraft. ARINC 629 → high‑performance commercial jets (e.g., B‑777). AFDX/ARINC 664 → modern wide‑body aircraft needing high‑speed networking. Collision‑avoidance system TCAS → commercial airliners, required for airspace with traffic density. Simplified TAAS → light GA aircraft without mandatory RA capability. --- 👀 Patterns to Recognize Frequency blocks: 118‑136 MHz → always VHF voice; look for 8.33 kHz spacing in European charts. ARINC numbers: 4xx → data bus protocols; higher numbers (e.g., 629, 664) → newer, higher‑speed. “‑wire” terminology: indicates electronic actuation (fly‑by‑wire, power‑by‑wire). “‑bus” suffix: points to a digital communication network (e.g., ARINC 825 CAN bus). --- 🗂️ Exam Traps Confusing channel spacing – picking 25 kHz for a European question (should be 8.33 kHz). Assuming GPWS includes forward‑looking terrain – only TAWS provides that capability. Mixing up ADS‑B and TCAS – ADS‑B broadcasts position; TCAS actively interrogates for collision avoidance. Selecting ARINC 429 for a Boeing 777 – the 777 uses ARINC 629 (or AFDX) for high‑speed data. Believing all aircraft use 28 V DC – large airliners use 115 V, 400 Hz AC for high‑power avionics. ---