FAA A&P Mechanic common mistakes
FAA A&P Mechanic · Understand the traps and how to avoid them.
Reads the stem, recognises a familiar true statement in the options, and selects it without registering a qualifier such as EXCEPT, NOT, FIRST, or LEAST likely.
Many written items test the negative case, and once a true statement appears the brain pattern-matches to it and stops reading the stem's qualifier.
What to do instead
Underline or silently repeat the qualifier before looking at any option. After choosing, substitute the answer back into the stem as a full sentence ('The item that is NOT required is...') and confirm it makes sense before moving on.
Solves weight-and-balance items by averaging the arms of the loaded items instead of multiplying each weight by its arm and summing moments.
CG problems superficially resemble averaging problems, and under time pressure the moment column feels like extra work, so it gets dropped.
What to do instead
Always lay out three columns: weight, arm, and moment (weight x arm). Sum weight and sum moment separately, then CG = total moment / total weight. Sanity-check that the result falls between the smallest and largest arm in the table.
Applies the 100-hour inspection rule to an aircraft described as privately operated, or applies the annual rule to an aircraft carrying persons for hire, without checking which trigger condition the stem actually describes.
Both intervals involve the same paperwork and both are described with similar wording, so the number is recalled but the condition that activates it is not.
What to do instead
Memorise inspection requirements as a table of triggers rather than isolated numbers: annual applies to all aircraft; 100-hour is tied to specific operations such as carrying persons for hire or giving flight instruction for hire; progressive programs are an approved alternative. Match the stem to the trigger first, then the interval.
Substitutes milliamps, kilo-ohms, or microfarads straight into Ohm's law and power formulas without converting to base units, producing an answer off by a factor of 1,000 or more.
Distractor options are usually scaled the same way as the givens, so the wrong arithmetic still looks like a plausible choice; prefixes get read as decoration rather than as multipliers.
What to do instead
Write every quantity in base units (A, V, ohms, W) before substituting, then convert the result back into the units the options use. Keep a prefix reference in memory: micro = 10^-6, milli = 10^-3, kilo = 10^3, mega = 10^6.
Selects 7075-T6 when the item asks which aluminium alloy has the best corrosion resistance, or picks 2024 for a part that must be formed easily, basing the choice on strength alone.
7075 is remembered as 'the strong one' and 2024 as 'aircraft aluminium', so the property actually being asked about gets silently replaced by a strength ranking.
What to do instead
Learn the alloys as trade-offs, not superlatives: 2024 has high strength but poor corrosion resistance and is normally used clad; 7075 has the highest strength and the poorest corrosion resistance and is not weldable; 6061 has good corrosion resistance and is easily formed and welded. Answer the property named in the stem.
Mislabels intergranular corrosion as exfoliation (or the reverse) and then selects the wrong inspection or removal action for the location described in the stem.
Both attack the grain boundaries of aluminium and both are described with words like lifting, flaking, and powdery, so the distinguishing visual and location cues get glossed over.
What to do instead
Anchor each type to a picture and a place: intergranular attacks along grain boundaries in thick sections and often looks like grey powder or a sugary surface; exfoliation is the severe layered form where material lifts and flakes away from the surface; galvanic occurs where dissimilar metals touch. Identify the type from the description first, then match the treatment to the depth of attack.
Treats a system relief valve and a pressure regulator as interchangeable components, or assumes the pump itself sets system pressure.
Both are valves that control pressure, and both appear in the same chapter of any study guide, so the functional difference is blurred.
What to do instead
Ask what the component must do. Preventing damage at an overpressure limit is a relief valve; holding a regulated operating pressure during normal flow is a regulator or unloading valve. Remember that a constant-displacement pump delivers volume, and pressure is created by the restriction downstream of it.
States that leaning the mixture always raises exhaust gas temperature, or treats peak EGT as the correct setting at every power level.
The phrase 'lean to peak EGT' is memorised as a rule without the shape of the curve that produces it, so the rich side and the lean side of peak are treated as the same.
What to do instead
Sketch the EGT versus fuel flow curve every time: leaning from full rich raises EGT, peak is a single point, and leaning further past peak lowers EGT. Then apply the accepted targets: approximately 100 degrees F rich of peak for best power, and at or lean of peak for best economy only within the engine manufacturer's limits.
Judges a magneto check only by whether the RPM drop falls inside a memorised range, without recording which magneto was selected, the drop on each, and the difference between them.
The published limits are remembered as one number, so the diagnostic content of the check, the drop pattern, is discarded.
What to do instead
For every magneto check note three things: which magneto is selected, the RPM drop on that magneto, and the differential between the two. Use the airframe or engine manufacturer's limits for both figures, then read the pattern: an excessive drop points to an ignition fault on the selected magneto, while no drop or rough running when selecting one magneto points to a grounding or switch problem.
Uses N1 and N2 interchangeably, or treats EGT on a turbine engine as a control input the way mixture is on a reciprocating engine.
Both tachometers read in percent RPM and sit side by side on the same panel, and the pilot's power lever feels analogous to a throttle, so the roles of the two spools and of EGT get conflated.
What to do instead
For each engine type, state which spool sets power and which is the limiting indicator: on most turbofans N1 is the power reference and N2 is the high-pressure spool; on turboprops the gas generator speed (Ng) is usually the reference. EGT is monitored against limits, never leaned to a target. Apply the same parameter logic to start malfunctions: a hung start is RPM stalling below idle, a hot start is EGT exceeding its limit.