Iran CAO Part-66 AMT Theory common mistakes
Iran CAO Part-66 AMT Theory · Understand the traps and how to avoid them.
When computing a wire's resistance or a resistor network, the candidate adds resistances in parallel and applies the reciprocal rule to series circuits, then carries the wrong value into a voltage-drop or power check.
Under time pressure the formulas are recalled as a pair without a physical anchor; the candidate remembers 'reciprocals' but not which configuration they belong to, and never sanity-checks that a parallel combination must be smaller than the smallest branch.
What to do instead
Before calculating, sketch the current paths and state aloud whether the same current flows through each element (series, add) or the same voltage sits across them (parallel, reciprocal add). Always finish with the bounding check: series result must exceed the largest element, parallel result must be below the smallest. Practise five mixed networks per session until the check is automatic.
The candidate treats an AC magnitude as a phasor sum, adding scalar RMS values of voltages across a resistor and a capacitor or inductor as if they were in phase, instead of combining them vectorially.
DC habits dominate early study; the candidate has memorised 'V = V1 + V2' from series DC circuits and has not internalised that reactive elements shift phase by 90 degrees, so the arithmetic feels correct.
What to do instead
For every AC series circuit, draw the phasor triangle first and use Vtotal = sqrt(VR^2 + (VL - VC)^2). Check that the total always lies between the largest component and the arithmetic sum. Work three RLC examples with numbers until the triangle, not the formula, drives the answer.
In basic aerodynamics items the candidate confuses angle of attack with pitch attitude or climb angle, and then mispredicts how lift, stall speed and load factor change in a turn or with flap extension.
Everyday language treats 'nose up' and 'high angle of attack' as synonyms; the candidate answers from intuition about aircraft attitude rather than from the relationship between chord line and relative airflow.
What to do instead
Redraw the chord line and relative airflow for each scenario before answering, and state the angle between them explicitly. For turn and flap questions, write the load-factor or CL term into the lift equation and see which quantity must change to hold altitude. Drill the distinction with three contrasting cases: level cruise, climbing at constant angle of attack, and a level turn.
In helicopter items the candidate applies fixed-wing stall and lift reasoning, treating translational lift, dissymmetry of lift and retreating-blade stall as if they followed aeroplane rules, and picks answers that ignore rotor RPM and inflow changes.
Most study material and prior intuition is aeroplane-based; rotorcraft-specific effects are taught late and in fewer hours, so the candidate defaults to the familiar fixed-wing model.
What to do instead
Build a one-page rotor map: forward flight gives advancing blade high dynamic pressure and retreating blade low, corrected by flapping and blade pitch; translational lift appears as the rotor leaves its own downwash; retreating-blade stall appears at high speed or high load with low RPM. For each question, identify airspeed, RPM and load factor first, then reason from that map.
The candidate answers human-factors questions with moral judgements ('the mechanic was careless') or with the single most obvious cause, rather than identifying the systemic and psychological factors in the scenario such as fatigue, complacency, pressure, or inadequate lighting and supervision.
The exam presents short vignettes and the candidate reads them as blame stories; the SHELL and dirty-dozen vocabulary has been memorised as a list but not practised as an analytical lens.
What to do instead
Answer in two steps: name the specific human-factor category the scenario illustrates, then name the organisational or environmental contributor. Reject any option that assigns fault without a mechanism. Practise by rewriting each vignette into a one-line 'factor leads to error leads to outcome' chain before looking at the options.
On aviation-legislation items the candidate mixes up who may certify a maintenance release, what an approved organisation versus a certifying staff authorisation permits, and which findings must be reported and to whom, answering from general impressions of 'the authority approves everything'.
The regulation text is dense and cross-referenced, and candidates study it as prose rather than as a set of actor-permission pairs; similar-sounding terms such as approval, authorisation and certification blur together.
What to do instead
Build a two-column table of actors (authority, approved maintenance organisation, certifying staff, pilot-owner) against actions (issue maintenance release, approve modification, extend interval, report occurrence), and fill it from the regulation text once. Rehearse by covering one column and reciting the other. Treat every question as 'which actor, which action, which document'.
When reading a torque wrench, micrometer, vernier calliper or feeler gauge item, the candidate reports the value without applying the instrument's resolution, zero error or unit conversion, and rounds to the nearest convenient number.
Workshop habit is to read to the nearest mark and move on; exam items deliberately place the reading between graduations or supply a zero offset, and candidates rush the arithmetic under time pressure.
What to do instead
Use a fixed reading routine: note the unit and resolution, read the main scale, add the fractional scale, subtract any zero error, then convert. Write the resolution beside the answer and check the answer is a whole number of resolutions. Time yourself on ten readings per session until the routine takes under a minute.
In digital-techniques and instrument-system items the candidate confuses the function of a logic gate or flip-flop with a bus or memory element, or misidentifies which ARINC or data-bus characteristic is being described, choosing a plausible-sounding but wrong layer of the system.
The domain spans logic, numbering systems, data buses and displays, and candidates memorise symbols without the underlying behaviour, so similar terms such as latch, register, multiplexer and transceiver collapse into one another.
What to do instead
Learn each device by its truth table and its role in a signal chain, not by its symbol. For bus questions, separate physical layer, protocol and message content, and state which one the question targets. Draw a simple chain from sensor through converter, bus and display, and place each term on it.
On materials and hardware items the candidate selects a fastener, lockwire practice or composite repair method by appearance or by what is common on the hangar floor, ignoring grip length, thread specification, material compatibility or the approved data requirement.
Familiarity with a few hardware types leads to pattern-matching; candidates answer 'what looks right' rather than checking the specification, and they underweight that any repair must follow approved or acceptable data.
What to do instead
For every hardware question, run three checks: correct specification (part number or standard), correct physical fit (grip length, diameter, thread), and correct approval basis (approved data or acceptable means of compliance). Where the question describes a repair, eliminate any option that lacks a data reference. Practise by classifying twenty fasteners by specification before answering anything about them.
In maintenance-practice and structures-and-systems items the candidate confuses scheduled and unscheduled maintenance concepts, or misreads a system schematic so that a component is placed in the wrong subsystem, for example mixing hydraulic, pneumatic and electrical supply paths or misidentifying which control surface a system moves.
System knowledge is often learned as isolated component lists rather than as connected flows; under exam pressure the candidate recalls a component's name but not its position in the chain, and maintenance terminology such as check, inspection and test is treated loosely.
What to do instead
For each major system, draw the flow from source through control to actuator and back, labelling the energy medium and the indication the flight deck would show. For maintenance-practice questions, define the term in the option before judging it. Redraw one system per study session from memory and compare with the reference, correcting only the gaps.