FAA A&P Mechanic cheat sheet

Ohm's law: E = I × R, and power P = E × I. In a series circuit current is constant and voltages add; in a parallel circuit voltage is constant and branch currents add.

Weight and balance: moment = weight × arm (inch-pounds); CG = total moment ÷ total weight. The calculated CG must fall within the approved forward and aft limits.

Torque = force × perpendicular distance; 1 ft-lb = 12 in-lb. A straight in-line extension does not change the torque applied at the fastener.

Aluminum alloys resist corrosion through cladding (Alclad), chemical conversion coatings, or paint; dissimilar metals must be isolated to prevent galvanic corrosion.

An annual inspection is due every 12 calendar months and must be signed off by an A&P holding an Inspection Authorization.

A 100-hour inspection is required for aircraft carrying persons for hire or used for flight instruction for hire, and may be performed by any certificated A&P.

Safety wire is installed so any loosening tendency pulls the wire in the tightening direction; 0.020 to 0.032 inch wire is typical, with 6 to 8 twists per inch.

Nondestructive testing selection: magnetic particle for surface and near-surface flaws in ferromagnetic parts; dye penetrant for surface-breaking flaws in nonporous materials; eddy current for conductive materials.

A micrometer thimble reads to 0.001 inch; vernier calipers commonly read to 0.001 inch. Measurements are taken at room temperature to avoid thermal error.

Rivet layout: edge distance is at least 2D from rivet center to sheet edge; pitch is 4D to 6D in a single row and 3D to 4D between rows in multiple-row joints (D = rivet diameter).

2024-T3 aluminum has high strength with fair corrosion resistance; 7075-T6 is stronger but less corrosion resistant; 6061-T6 is weldable and corrosion resistant.

Typical transport-category hydraulic system pressure is 3,000 psi; a relief valve limits pressure and an accumulator absorbs surges and supplies flow during peak demand.

Control cable tension is measured with a tensiometer and adjusted to the temperature-corrected value in the maintenance manual; surface travel is then checked against rigging tolerances.

Pneumatic deice boots on the leading edges inflate at roughly 15 to 20 psi to crack and shed ice; they are checked for proper inflation sequence and leaks.

Nose gear shimmy is controlled by a shimmy damper; torque links maintain wheel alignment, and oleo struts use oil plus a nitrogen precharge to absorb landing loads.

Fuel tank vents prevent vapor lock and allow the tank to maintain atmospheric pressure; sump drains are sampled for water and sediment before flight.

Bonding jumpers provide a low-resistance path between structural components to drain static electricity and complete electrical return circuits.

Grade A cotton fabric is finished with dope; approved synthetic covering systems require their specific adhesives, primers, and topcoats per the STC instructions.

Four-stroke cycle: intake, compression, power, exhaust. Two crankshaft revolutions (720°) complete one cycle, and valve overlap near top dead center improves volumetric efficiency.

Compression ratio = (cylinder displacement + clearance volume) ÷ clearance volume; higher ratios raise power and efficiency but demand higher-octane fuel.

Stoichiometric fuel/air ratio is about 15:1 by weight; mixtures richer than stoichiometric (near 12:1) produce best power, while leaner mixtures improve economy.

On a four-stroke engine the magneto turns at one-half crankshaft speed and fires each cylinder once per cycle; ignition timing is set before top dead center.

Turbine engine monitoring: N1 is low-pressure compressor or fan speed, N2 is high-pressure rotor speed, and EGT or ITT indicates combustion temperature against published limits.

Propeller blade angle is measured from the plane of rotation; a constant-speed propeller uses a governor to vary blade angle and hold a selected RPM.

Reciprocating engine oil grades are given by viscosity number (100 corresponds to SAE 50); ashless dispersant oil is standard for most horizontally opposed engines.

Excessive cylinder head temperature can result from a lean mixture, improper ignition timing, or missing cooling baffles; CHT limits are published in the maintenance manual.

Exhaust system cracks or loose connections can leak carbon monoxide into the cabin; exhaust stacks and mufflers are inspected for cracks, erosion, and security.