FAA Aviation Mechanic - General (AMG) cheat sheet

Ohm's law: E = I × R; power P = E × I = I²R = E²/R, with E in volts, I in amperes, R in ohms.

In a series circuit the current is the same through every component, the voltage drops add, and total resistance equals the sum of the resistances.

In a parallel circuit the voltage is the same across every branch, branch currents add, and total resistance is less than the smallest branch resistance.

A voltmeter is connected in parallel with the load; an ammeter is connected in series and has very low internal resistance.

Continuity and resistance checks are made with an ohmmeter with the circuit de-energized, because a powered circuit can damage the meter.

One horsepower equals 746 watts; a 28-volt, 1-horsepower motor draws about 26.6 amperes at 100 percent efficiency.

Aircraft AC systems commonly use 115/26 volts at 400 Hz; in an inductor current lags voltage, and in a capacitor current leads voltage.

The resistance of a metal conductor increases as temperature increases; a capacitor blocks DC and passes AC.

A 12-volt lead-acid battery has six cells at about 2.1 volts each, and the specific gravity of the electrolyte indicates state of charge.

The title block, normally in the lower right corner, gives the drawing number, scale, date, and latest revision status.

In third-angle orthographic projection the top view is drawn above the front view, and the right-side view is drawn to the right of the front view.

Hidden edges are shown as short dashes, center lines as a long-short-long pattern, and dimension lines with arrowheads at each end.

Section views use cross-hatching to show internal structure; a break line (wavy or zigzag) shows a portion removed for clarity.

A detail drawing shows one part with all dimensions; an assembly drawing shows the relationship of parts and carries a bill of materials.

A schematic shows the logical flow of a system and does not indicate physical location, wire length, or component size.

Do not scale a drawing - use the stated dimensions; drawing changes are identified by a revision letter or symbol with a description.

An isometric drawing shows all three dimensions in one view with lines drawn at 30 degrees to the horizontal, and it is not drawn to scale.

A center line marks an axis of symmetry, and a phantom line (long dash, two short dashes) shows alternate positions or adjacent parts.

Moment = weight × arm; CG arm = total moment ÷ total weight; the datum is the fixed reference point from which all arms are measured.

Arms forward of the datum are negative and arms aft are positive - the sign must be carried through every moment calculation.

Useful load = maximum gross weight − empty weight; empty weight includes unusable fuel and full engine oil.

Tare weight (blocks, chocks, slings) must be subtracted from the scale readings before computing empty weight and CG.

Weight-shift formula: weight moved ÷ total weight = CG shift ÷ the distance the weight is moved.

An aft CG reduces longitudinal stability and may make the airplane unrecoverable; a forward CG limits elevator authority and raises stall speed.

The aircraft must be within weight and CG limits at takeoff, in flight, and at landing; the most adverse loading is checked, not an average.

Any alteration that changes weight or CG requires a new or amended weight and balance report.

Corrective ballast must be fixed in place, and its weight and location become a permanent part of the empty weight and CG.

Standard aircraft AN and MS flares are 37 degrees; a 45-degree automotive flare or nut must never be substituted.

Aluminum alloy tubing selection: 3003 and 5052-O for low pressure, 1100 for general low pressure, and 6061-T6 for higher-pressure hydraulic systems.

Cut tubing square, deburr, and keep the cut end free of cracks; minimum bend radius is generally 2 to 3 times the tube outside diameter.

A flareless (MS) fitting uses a ferrule that is preset onto the tube; once preset, the fitting cannot be reused with a different tube.

Flexible hose is identified by a lay line; the assembly must not be twisted, kinked, or bent tighter than its rated bend radius.

Use two wrenches when tightening a B-nut - one on the fitting body and one on the nut - to avoid twisting the tube.

Teflon hose is used for high-temperature and phosphate-ester (Skydrol) systems; ordinary rubber hose is not compatible with Skydrol.

Support tubing with clamps at approved intervals to prevent vibration and chafing, and route lines so structure movement does not stress them.

AN flare fittings are rated to about 3,000 psi; torque values come from the manufacturer's table and are applied with a torque wrench.

2024 (copper-bearing) and 7075 (zinc-bearing) aluminum alloys are high strength but have low corrosion resistance; 2024 is normally supplied Alclad.

5052 is the most corrosion-resistant common aircraft aluminum; 6061 is heat treatable and weldable and is used for tubing and fittings.

In the four-digit designation the first digit is the principal alloying element, and the temper letter/digits (O, T3, T6, H) give heat-treat condition.

Dye penetrant finds surface flaws in nonporous materials; magnetic particle inspection works only on ferromagnetic parts such as steel.

Eddy current detects surface and near-surface defects in conductive materials, while ultrasonic and radiographic methods detect internal defects.

Aluminum is solution heat treated and quenched, then naturally aged (T3) or artificially aged in an oven (T6); annealing softens metal for forming.

Solid rivet alloys are marked on the head: 2117-T4 (AD) has one dimple, 2017-T4 (D) one raised dot, and 2024-T4 (DD) two raised dashes.

A dull thud on a tap test or a shadow on ultrasonic inspection indicates delamination or voids in composite structure.

Magnesium chips and dust are highly flammable; use a Class D extinguisher and never apply water to a magnesium fire.

Before fueling, connect the bonding cable from the fuel source to the aircraft first, then ground the aircraft; remove the ground and bond last.

No smoking, open flame, or operating radar within 50 feet of fueling, and never fuel with engines, APU, or combustion heaters running.

Avgas 100LL is dyed blue, grade 100 is green, and Jet A/Jet A-1 are undyed or straw-colored; avgas and jet fuel are never intermixed.

Oxygen equipment must be free of oil, grease, and sealant, and oxygen servicing is kept at least 25 feet from fueling operations.

Before jacking, confirm the aircraft is within its jacking CG limits, use only approved jack points, keep it level, and install safety stands.

Never turn a nosewheel beyond its published turning limits during towing; use a tow bar with a shear pin and a qualified guide.

Tie-down: secure the control surfaces with locks or straps, chock the wheels, and moor with three-point tie-downs into the prevailing wind.

Fuel sumps are drained before flight to remove water and sediment; Prist (anti-icing additive) may be added to jet fuel.

Dry, oil-free nitrogen is used to service tires and struts because it eliminates oxygen and moisture from the system.

Galvanic corrosion occurs where dissimilar metals meet in the presence of an electrolyte; isolate them with primer, sealant, or plating.

Concentration-cell (oxygen-concentration) corrosion occurs in crevices and under deposits where oxygen is excluded - keep surfaces clean and sealed.

Exfoliation is intergranular corrosion that lifts layers of rolled or extruded aluminum; pitting is localized deep attack with a small surface opening.

Remove corrosion with aluminum wool, abrasive paper, or a nylon abrasive pad - never use steel wool or a steel wire brush on aluminum.

After corrosion removal, apply a conversion coating such as Alodine, then refinish with primer and topcoat.

Water-displacing corrosion-inhibiting compounds are sprayed into internal structure, seams, and crevices to prevent hidden corrosion.

Anodizing builds an electrolytic oxide film on aluminum, and Alclad sheet uses a pure aluminum surface layer for protection.

Rinse salt deposits with fresh water and avoid strong alkaline cleaners on aluminum, plastics, and fabric-covered surfaces.

High-risk inspection areas include the battery compartment, wheel wells, bilge areas, exhaust and engine zones, and under galleys and lavatories.

Circle area = πr² and circumference = 2πr; triangle area = ½ × base × height; cylinder volume = πr²h.

Pythagorean theorem: a² + b² = c² for a right triangle, used to solve for an unknown side.

1 inch = 25.4 millimeters, 1 foot = 12 inches, and 1 U.S. gallon = 231 cubic inches = 128 fluid ounces.

Weight per gallon: avgas about 6.0 lb, jet fuel about 6.7 lb, engine oil about 7.5 lb, water about 8.35 lb.

Temperature conversion: °F = (°C × 9/5) + 32 and °C = (°F − 32) × 5/9.

Work = force × distance; power = work ÷ time; 1 horsepower = 33,000 ft-lb/min = 550 ft-lb/sec = 746 watts.

Density = mass ÷ volume, and specific gravity is the ratio of a substance's density to the density of water.

Convert a fraction to a decimal by dividing, and a decimal to a percentage by multiplying by 100; ratio and proportion scale units and mixtures.

Carry significant figures through a calculation and round the answer only to the accuracy of the least precise given value.

FAR 43.9: a maintenance entry must state the work performed, the date completed, and the name, certificate type and number, and signature of the person.

FAR 43.11: an approval for return to service after an annual or 100-hour inspection includes the date, total time in service, and signature.

FAA Form 337 records a major repair or major alteration; a copy is submitted to the FAA and one is kept with the aircraft records.

FAR 91.417: the owner or operator must keep maintenance, alteration, and inspection records and retain them for at least 1 year after the work is done or until superseded.

Required records include airframe, engine, propeller, and appliance logbooks, plus a current weight and balance report and equipment list.

Each Airworthiness Directive compliance entry must show the AD number, method of compliance, date, and aircraft total time in service.

Records must be made available for inspection by the FAA and NTSB and are transferred with the aircraft when it is sold.

No entry may be made for work not performed; falsifying a maintenance record is grounds for suspension or revocation of the certificate.

The preventive maintenance items an owner/operator may perform are listed in FAR Part 43, Appendix A, paragraph (c).

Advisory Circulars are non-mandatory guidance; AC 43.13-1B covers acceptable methods, techniques, and practices for aircraft inspection and repair, and AC 43.13-2B covers alterations.

Airworthiness Directives are mandatory rules issued under 14 CFR Part 39 and published in the Federal Register; emergency ADs can require compliance before further flight.

A Type Certificate Data Sheet lists the approved operating limitations, specifications, and eligible equipment for an aircraft, engine, or propeller type design.

Manufacturer maintenance manuals, structural repair manuals, overhaul manuals, and illustrated parts catalogs provide approved procedures and part numbers.

Service bulletins are the manufacturer's recommendations and are mandatory only when adopted by an AD or required by an operator's approved program.

Items in the Airworthiness Limitations Section of the instructions for continued airworthiness are mandatory and must be accomplished exactly as written.

A Special Airworthiness Information Bulletin is advisory information from the FAA and is not a regulation.

14 CFR Parts 21, 39, 43, 65, and 91 are the primary regulations affecting a mechanic's work.

The Summary of Airworthiness Directives indexes ADs; applicability depends on the make, model, and serial number of the affected product.

FAR 65.81: a certificated mechanic may perform maintenance, preventive maintenance, and alterations and may approve for return to service the work he or she performed.

A mechanic may not approve an aircraft for return to service after an annual inspection unless the mechanic holds an Inspection Authorization.

FAR 65.83: to exercise rating privileges, a mechanic must have had at least 6 months of practical experience in the preceding 24 months in the work performed.

FAR 65.121: a mechanic must keep a record of each inspection, repair, and alteration approved for return to service and retain it for at least 2 years.

An A&P mechanic may perform and approve a 100-hour inspection for return to service; an annual inspection requires an IA.

Instrument repairs require an instrument rating, and radio/avionics repairs require a repairman certificate or other FAA authorization.

A major alteration requires approved data, an FAA Form 337, and approval for return to service by an IA or other authorized person.

Preventive maintenance may be performed by a certificated mechanic, or by a pilot certificated under Part 61 on an aircraft the pilot owns and operates that is not operated under Part 121 or 135.

Part 65 requires the certificate holder to notify the FAA within 30 days of a change of permanent address.