NCAA AME Avionics cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. Use for voltage-drop and load checks on 28 V DC and 115 V AC 400 Hz aircraft buses.

Series circuit: total resistance adds (R_T = R₁ + R₂ + …), current is common, voltage divides. Parallel: 1/R_T = 1/R₁ + 1/R₂ + …, voltage is common, current divides.

Wire sizing is governed by current-carrying capacity, allowable voltage drop (commonly ≤ 2 V on 28 V DC circuits), bundle derating, and temperature/altitude correction.

Bonding resistance limits keep fault current paths low-impedance; a typical airframe bond target is ≤ 2.5 mΩ (0.0025 Ω) at primary structure joints, verified with a four-wire micro-ohmmeter.

Insulation resistance testing uses a megohmmeter at a specified DC test voltage (commonly 250 V or 500 V DC); record ambient temperature and humidity because both affect readings.

ARINC 429 is a unidirectional, differential, 32-bit word bus at 12.5 or 100 kbit/s; ARINC 629 and AFDX/Ethernet are bidirectional, so label, parity, and SSM (sign/status matrix) bits must be checked on readback.

A 400 Hz AC system allows smaller magnetic components than 50/60 Hz for the same power; frequency, phase sequence, and phase imbalance are the key parameters to verify on inverters and TRUs.

Electrostatic discharge control: ground the technician through a wrist strap with a 1 MΩ series resistor, use dissipative work surfaces, and store line-replaceable units in shielded bags.

Built-in test (BIT) results are advisory only; a 'no fault found' BIT result does not replace a functional test against the maintenance manual tolerances.

Maintenance is defined as inspection, overhaul, repair, preservation, and replacement of parts, but excludes preventive maintenance; the distinction determines who may sign.

Preventive maintenance is limited, simple, and does not involve complex assembly operations; avionics tasks generally fall outside preventive maintenance and require certificated personnel.

A major alteration or major repair requires approved technical data (STC, TC holder data, or FAA-approved data) and Form 337 or equivalent approval before return to service.

A minor alteration or minor repair may be returned to service by an appropriately rated person using acceptable data or standard practices, with a maintenance record entry.

Airworthiness directives are mandatory; an AD affecting an avionics item must be complied with within the stated interval, and recurring ADs must be tracked and recorded.

Parts must be traceable: airworthy (new, overhauled, or serviceable with proper documentation) or produced under an approved production approval; suspected unapproved parts must be quarantined and reported.

Instructions for continued airworthiness (ICA) from the manufacturer or STC holder define the approved maintenance tasks, intervals, and limits for installed avionics.

Configuration control: any software or hardware change to avionics requires verification that the approved configuration (part number, mod status, software load) matches the aircraft records.

A maintenance record entry must include the work performed, date completed, and the name and certificate number of the person approving the work for return to service.

The description must be in sufficient detail to allow a person unfamiliar with the work to determine its airworthiness status; 'tested OK' is insufficient without reference to the approved data used.

Inspection programs include annual inspection, 100-hour inspection (where required), progressive inspection, and continuous airworthiness maintenance programs; avionics items are covered by the applicable checklist.

Return to service is a certification act: the signer certifies the work was performed using approved data and the item is airworthy, so the signer must hold the appropriate rating and authority.

Records retention: maintenance records are retained until the work is superseded by equivalent work or for the period specified by regulation (commonly one year for many maintenance entries, longer for certain inspections and major alterations).

A discrepancy found during inspection must be recorded and corrected or deferred under an approved minimum equipment list (MEL) or configuration deviation list (CDL) before flight.

An inspection performed by a certificated mechanic is documented with the inspection type, date, aircraft total time, and the signature and certificate number of the inspector.

Independent checks: flight-critical avionics (e.g., pitot-static, transponder, altimeter) require specific tests and certifications, often by an appropriately rated repair station with test equipment calibration records.

An aircraft maintenance engineer licence is issued with ratings (airframe, powerplant, avionics, or as defined by the authority); the holder may certify work only within the ratings held.

Eligibility typically requires a minimum age (commonly 18), specified training or experience, and passing knowledge and practical examinations.

Experience requirements are usually expressed in months of practical maintenance experience, with a portion obtained on the category of aircraft or systems for which the rating is sought.

The licence holder is responsible for ensuring the work certified was performed by themselves or under their direct supervision, and that approved data was used.

Privileges are limited by the ratings and any limitations on the licence; exceeding the rating scope is a violation even if the person is technically competent.

Recency and currency requirements: many authorities require recent experience or recurrent training to maintain certification privileges.

A separate repair station or approved maintenance organization rating is required to perform certain specialized avionics work (e.g., avionics/instruments) and to issue approvals for return to service.

Recordkeeping for the individual: logbooks of experience and training are the evidence used to support licence application, rating addition, and renewal.