The NCATT Aircraft Electronics Technician (AET) certification is the aviation industry's standard credential for avionics professionals who install, maintain, and troubleshoot electronic systems on civil aircraft. Issued by the National Center for Aerospace and Transportation Technologies, the AET exam covers electrical fundamentals, digital logic, aircraft communication and navigation systems, avionic bus architectures, and FAA regulatory requirements.

Electrical fundamentals form the bedrock of all avionics work. Ohm's Law (V = IR) and its power corollaries (P = VI, P = I²R, P = V²/R) govern circuit analysis in both DC and AC domains. Kirchhoff's Voltage Law (the sum of voltages around any closed loop equals zero) and Kirchhoff's Current Law (the sum of currents entering a node equals the sum leaving) are applied when analyzing multi-branch circuits. Capacitors store energy in an electric field (C = Q/V) and act as open circuits to DC while passing AC; inductors store energy in a magnetic field and oppose changes in current. In AC circuits, impedance (Z) combines resistance, capacitive reactance (X_C = 1/2πfC), and inductive reactance (X_L = 2πfL) in series and parallel configurations.

Digital logic underpins every modern avionics LRU (Line Replaceable Unit). AET candidates must understand binary-to-decimal and hexadecimal conversions, the behavior of basic logic gates (AND, OR, NOT, NAND, NOR, XOR, XNOR), Boolean algebra simplification including De Morgan's theorems, and sequential logic elements including SR, D, and JK flip-flops. Microprocessors and microcontrollers used in avionics execute fetch-decode-execute cycles and rely on bus architecture (data bus, address bus, control bus) to communicate with memory and peripherals.

Aircraft communication systems require precise understanding. VHF communications operate in the 118–137 MHz band and are the primary voice communications medium for civil aviation; UHF is used by military and some search-and-rescue operations. SELCAL (Selective Calling System) allows ground stations to alert a specific aircraft via a coded tone sequence, eliminating the need for continuous audio monitoring on long overwater flights. ACARS (Aircraft Communications Addressing and Reporting System) provides digital data link communications between aircraft and airline operations centers over VHF, HF, or satellite, enabling automated transmission of OOOI times, engine data, and weather reports.

Navigation systems are central to the AET exam. VOR (VHF Omnidirectional Range) transmits 360 radials from a ground station; airborne receivers display bearing and course deviation. ILS (Instrument Landing System) combines a localizer (lateral guidance) and glide slope (vertical guidance) to provide precision approaches down to CAT III minimums. ADF (Automatic Direction Finder) uses NDB (Non-Directional Beacon) ground stations in the LF/MF band and displays a relative bearing to the station. GPS receivers derive position from pseudorange measurements to at least four satellites; WAAS augmentation improves accuracy to support LPV approaches. TCAS II uses Mode S transponder interrogation to detect conflicting traffic and issue Resolution Advisories (RAs) to pilots to maintain vertical separation.

Flight instruments in modern glass-cockpit aircraft use solid-state sensors rather than traditional mechanical gyroscopes. The AHRS (Attitude and Heading Reference System) uses MEMS accelerometers and ring laser or fiber-optic gyros to compute pitch, roll, and magnetic heading with no spinning parts. The ADC (Air Data Computer) calculates airspeed, altitude, and vertical speed from pitot-static inputs, replacing the mechanical instruments of older aircraft. Understanding the pitot-static system — pitot tube (total pressure), static port (ambient pressure), and the derived parameters — is essential for both troubleshooting and the AET exam.

Avionic bus systems are the nervous system of modern aircraft. ARINC 429 is the most widely used digital data bus on civil transport aircraft, operating as a unidirectional 32-bit word serial bus at 12.5 kbps (low speed) or 100 kbps (high speed) using differential bipolar signaling. Because it is unidirectional, separate buses are required for each direction of data flow. ARINC 629, used on the Boeing 777, is a bidirectional bus that allows multiple transmitters and receivers on the same cable at 2 Mbps. MIL-STD-1553 is a military data bus standard operating at 1 Mbps with a command/response protocol and redundant bus architecture used in military avionics and some commercial applications.

Soldering and wire harness fabrication are hands-on skills tested conceptually in the AET exam. IPC-A-610 (Acceptability of Electronic Assemblies) defines three classes of workmanship: Class 1 (general electronics), Class 2 (dedicated service), and Class 3 (high-reliability, including avionics). Avionics work typically requires Class 3 compliance. MIL-SPEC wire (MIL-W-22759, for example) is specified for its high-temperature rating and weight savings. Proper crimping, wire routing, strain relief, and connector insertion force are all critical for airworthiness.

FAA regulations define the technician's legal authority and responsibilities. 14 CFR Part 43 governs maintenance, preventive maintenance, and alteration of civil aircraft and requires that all maintenance be performed by or supervised by an appropriately certificated individual, with a proper maintenance record entry made upon completion. 14 CFR Part 145 governs repair station certification, staffing, equipment, and quality control requirements. AET holders working at Part 145 repair stations must understand return-to-service authorization, inspector qualifications, and the documentation required to release aircraft back to service after avionics maintenance.