Iran CAO Part-66 AMT Theory cheat sheet

Order of operations: brackets, indices, multiplication/division left to right, addition/subtraction left to right; 2+3×4 = 14, not 20.

Scientific notation: a×10^n with 1≤|a|<10; multiply by adding exponents, divide by subtracting, and add exponents after aligning powers when adding numbers.

Powers and roots: a^m×a^n = a^(m+n); (a^m)^n = a^(mn); a^0 = 1; a^(−n) = 1/a^n; √(ab) = √a·√b.

Logarithms: log(ab) = log a + log b; log(a/b) = log a − log b; log(a^n) = n·log a; log_b x = ln x / ln b.

Right triangles: sin θ = opp/hyp, cos θ = adj/hyp, tan θ = opp/adj; Pythagoras c² = a² + b²; sin²θ + cos²θ = 1.

Sine and cosine rules for non-right triangles: a/sin A = b/sin B = c/sin C and a² = b² + c² − 2bc·cos A.

Percentage and ratio: percentage change = (new − old)/old × 100; a ratio a:b splits a total T into aT/(a+b) and bT/(a+b).

Area and volume: circle area πr², circumference 2πr, cylinder volume πr²h, sphere volume (4/3)πr³, cone volume (1/3)πr²h.

Unit conversion factors: 1 inch = 25.4 mm, 1 lb = 0.4536 kg, 1 kgf = 9.81 N, 1 US gal = 3.785 L, 0 °C = 273.15 K.

Newton's second law: F = ma; weight W = mg with g ≈ 9.81 m/s²; 1 N accelerates 1 kg at 1 m/s².

Kinematics with constant acceleration: v = u + at, s = ut + ½at², v² = u² + 2as.

Work, energy and power: W = Fs (force along displacement), KE = ½mv², PE = mgh, P = W/t = Fv.

Moment of a force = force × perpendicular distance; for equilibrium, sum of moments about any point is zero and sum of forces is zero.

Pressure: p = F/A in pascals; hydrostatic pressure p = ρgh; absolute pressure = gauge pressure + atmospheric pressure.

Gas laws: pV = nRT; at constant T, p₁V₁ = p₂V₂; at constant p, V₁/T₁ = V₂/T₂ with T in kelvin.

Heat: Q = mcΔT for sensible heat and Q = mL for latent heat; thermal expansion ΔL = αLΔT.

Density ρ = m/V; relative density compares a substance to water (1000 kg/m³); a body floats when its density is less than the fluid's.

Wave relation v = fλ; speed of sound in air ≈ 343 m/s at 20 °C, increasing about 0.6 m/s per °C rise.

Ohm's law V = IR; power P = VI = I²R = V²/R; energy in kWh = power in kW × time in hours.

Series circuit: R_total = R₁ + R₂ + …; current is common; voltage divides in proportion to resistance.

Parallel circuit: 1/R_total = 1/R₁ + 1/R₂ + …; voltage is common; current divides inversely with resistance.

Kirchhoff's laws: sum of currents at a node is zero; sum of voltages around a closed loop is zero.

Capacitance in farads: C = Q/V; series 1/C = 1/C₁ + 1/C₂; parallel C = C₁ + C₂; energy = ½CV².

Inductance in henries: series L = L₁ + L₂; parallel 1/L = 1/L₁ + 1/L₂; energy = ½LI²; induced emf e = −L(di/dt).

AC quantities: RMS = peak/√2 for a sine wave; frequency f = 1/T; reactance X_C = 1/(2πfC), X_L = 2πfL.

Impedance Z = √(R² + (X_L − X_C)²); at resonance X_L = X_C and Z = R with unity power factor.

Three-phase: line voltage = √3 × phase voltage in star connection; total power P = √3·V_L·I_L·cos φ.

Diode: conducts from anode to cathode when forward biased above ≈0.7 V (silicon) or ≈0.3 V (germanium); blocks reverse current.

Zener diode operates in reverse breakdown to regulate voltage; the series resistor limits current and dissipates the excess.

Bipolar transistor: base-emitter ≈0.7 V to conduct; collector current I_C = β·I_B; operates as switch (cut-off/saturation) or amplifier (active).

MOSFET is voltage-controlled; gate draws negligible steady current; used for high-current switching in power supplies and motor drives.

Operational amplifier: with negative feedback, gain = 1 + R_f/R_in for non-inverting and −R_f/R_in for inverting configuration.

Rectification: half-wave gives one pulse per cycle; full-wave bridge gives two; capacitor smoothing reduces ripple; ripple falls as C or load resistance rises.

Filters: low-pass passes frequencies below cut-off f_c = 1/(2πRC); high-pass passes above it; band-pass combines both.

Logic families: TTL nominal supply 5 V with logic thresholds around 0.8 V (low) and 2.0 V (high); CMOS has high input impedance and wider supply range.

Photodiode and LED: photodiode converts light to current in reverse bias; LED forward-biased emits light at a wavelength set by semiconductor band gap.

Number systems: binary to decimal by summing powers of 2; hexadecimal digit = 4 bits; octal digit = 3 bits.

Two's complement: invert bits and add 1 to negate; an n-bit signed range is −2^(n−1) to 2^(n−1) − 1.

Bus types: ARINC 429 is a one-way, 32-bit word, twisted-pair bus at 12.5 or 100 kbit/s; ARINC 629 and AFDX are bidirectional.

ARINC 429 label identifies the parameter; parity bit provides odd-parity error detection; only one transmitter per wire pair is permitted.

Data conversion: ADC resolution = full-scale range / 2^n; a 10-bit converter over 10 V resolves 10/1024 ≈ 9.8 mV per step.

Display types: CRT uses an electron beam and high voltage; LCD is low-power and uses polarisers; LED and OLED are solid-state emitters.

Electronic flight instrument systems: EADI shows attitude and flight director; EHSI shows heading, course, navigation and weather; symbol generator drives both.

Flight deck data buses: ARINC 429 for legacy line-replaceable units; AFDX (ARINC 664) is switched Ethernet with redundant virtual links.

Built-in test: power-up BIT runs at energisation, continuous BIT monitors in flight, and initiated BIT is commanded by maintenance action.

Aluminium alloys: 2024 (copper, good fatigue strength, low corrosion resistance) and 7075 (zinc, high strength) are clad with pure aluminium as Alclad for corrosion protection.

Steel designation: 4130 chromium-molybdenum steel is common for tube structures; heat treatment raises strength but reduces ductility.

Titanium is used where strength-to-weight and heat resistance matter; it is prone to galling and requires special cutting practice.

Composite: carbon fibre reinforced plastic has high specific strength; moisture absorption and galvanic corrosion with aluminium are key concerns.

Fastener grip length equals the thickness of material plus washer; the thread must not bear inside the shear plane of the joint.

Torque values are set by the manufacturer; a torque wrench must be calibrated and used on the nut unless specified, with prevailing torque for locknuts.

Locking devices: split pins, lockwire (double-twist, 6–8 twists per inch), tab washers, and self-locking nuts; none may be reused beyond stated limits.

Bearings: ball bearings carry radial and some axial load; roller bearings carry high radial load; taper rollers carry combined loads and need preload adjustment.

Corrosion types: galvanic between dissimilar metals, pitting on passive metals, stress corrosion in loaded high-strength alloys, and fretting at mating surfaces.

Maintenance documentation: task cards and worksheets must be signed by the person who performed the task; certification follows only after all steps are complete.

Torque and safety: use calibrated tools within their validity period; record actual torque values; apply lockwire or locking devices after final torque.

Precautions: disconnect electrical power, depressurise hydraulic and pneumatic systems, and fit control locks before work on flight controls.

Foreign object debris control: tool control, inventory checks and engine intake blanks prevent FOD damage.

Inspection methods: visual, borescope, dye penetrant (surface), magnetic particle (ferromagnetic surface/subsurface), eddy current (surface), ultrasonic (internal), radiography (internal).

Corrosion removal: blend out within allowable limits, restore protective finish; any blend beyond limits requires engineering disposition.

Fuel system safety: bonding and grounding before fuelling, no ignition sources, correct fuel grade, and water/sediment drain checks.

Maintenance error management: use checklists, duplicate inspection of critical assemblies, and clear shift handover records to reduce omissions.

Return to service requires a certificate of release to service issued by authorised certifying staff after maintenance and inspection are complete.

Bernoulli's equation for steady incompressible flow: p + ½ρv² + ρgh = constant; higher velocity gives lower static pressure.

Continuity equation: mass flow ρAv is constant along a streamtube; a smaller area gives higher velocity.

Lift L = ½ρV²SC_L; drag D = ½ρV²SC_D; both rise with the square of speed.

Angle of attack is the angle between the chord line and the relative airflow; lift increases with AoA up to the critical angle, then stalls.

Boundary layer: laminar flow has low skin friction; turbulent flow has higher friction but resists separation better.

Induced drag falls with increasing speed and rises with lift coefficient; parasite drag rises with the square of speed.

Centre of pressure moves forward as angle of attack increases on a cambered aerofoil.

Mach effects: at the critical Mach number local airflow reaches Mach 1; shock waves cause drag rise, buffet and possible control reversal.

Stability: static stability is the initial tendency to return to equilibrium; positive longitudinal stability requires the centre of gravity ahead of the neutral point.

Sensory systems: vision dominates flight deck information gathering; the eye's fovea gives detail but poor night sensitivity, so night vision uses off-centre viewing.

Hypoxia symptoms include euphoria, impaired judgement and cyanosis; time of useful consciousness at 35,000 ft is roughly 30–60 seconds.

Hypoxia types: hypoxic (altitude), hypaemic (anaemia), stagnant (G-loading), histotoxic (alcohol, cyanide).

Fatigue and circadian rhythm: alertness is lowest around 03:00–06:00 and 15:00–17:00; duty limits and rest manage risk.

Stress and workload: performance degrades at both very low and very high arousal; task saturation leads to omission of lower-priority tasks.

Human error models: the Swiss cheese model shows latent conditions aligning with active failures; the SHELL model covers software, hardware, environment and liveware.

Communication: readback and standard phraseology reduce error; expectation bias can cause a listener to hear what is expected rather than what was said.

Memory and attention: prospective memory lapses are reduced by checklists and written reminders; complacency rises with routine repetition.

Vision illusions: empty-field myopia, black hole approach and somatogravic illusion can cause misleading attitude perception without visual reference.

ICAO Annex 8 covers airworthiness of aircraft; Annex 1 covers personnel licensing; national authorities issue implementing regulations.

Part-66 aircraft maintenance licence categories are A, B1, B2, B3 and C, with subcategories; ratings are endorsed after meeting experience and examination requirements.

Category A certifies scheduled line maintenance and limited tasks; B1 covers mechanical and avionics simple tasks on aeroplanes; B2 covers avionics; C certifies base maintenance.

Certifying staff may issue a certificate of release to service only within the scope of their licence and the organisation's approval.

Continuing airworthiness: Part-M and Part-CAMO cover maintenance programmes, airworthiness directives, and the airworthiness review certificate.

Airworthiness directives are mandatory; service bulletins are normally advisory unless made mandatory by the authority or operator.

Maintenance records must be retained and traceable; the CRS records the work performed, date, and identity of certifying staff.

Minimum equipment list allows dispatch with specified equipment inoperative under stated conditions; it is approved for the operator.

EASA Part-145 organisations must have a quality system, approved procedures, trained staff and a maintenance data control process.

Primary controls are ailerons, elevators and rudder; secondary controls are flaps, slats, spoilers and trim; flaps increase lift and drag and lower stall speed.

Fly-by-wire replaces mechanical linkage with computers and actuators; normal, alternate and direct law give progressively less protection and different handling.

Hydraulic systems use Skydrol-type phosphate ester fluid; it is toxic and attacks some paints; seals and hoses must be compatible.

Pneumatic system supplies engine bleed air for air conditioning, pressurisation and anti-icing; bleed valves regulate pressure and temperature.

Pressurisation: cabin pressure is controlled by outflow valves; cabin altitude and differential pressure are limited by the pressure schedule.

Electrical power: AC generators via constant-speed drives or variable-frequency generators, with transformer rectifier units supplying DC and batteries as emergency source.

Fuel system: vented tanks, boost pumps, crossfeed and jettison where fitted; fuel quantity and temperature indications are monitored.

Landing gear: oleo struts absorb landing loads; antiskid and auto-brake control wheel speed; gear position and warning systems indicate unsafe states.

Ice protection: thermal anti-ice uses hot air on leading edges; de-icing boots inflate; fluid systems protect propellers and windshields.

Rotor thrust T = ½ρA(ΩR)²C_T; induced velocity in hover v_i = √(T/(2ρA)) for momentum theory.

Dissymmetry of lift in forward flight is equalised by blade flapping and cyclic feathering; retreating blade stalls at high speed or high load.

Translational lift occurs as the rotor leaves its own downwash, improving efficiency typically above about 15–20 kt.

Ground effect reduces induced velocity near the surface and lowers power required; it is lost at a height roughly equal to the rotor diameter.

Autorotation: the rotor is driven by upward airflow; the pilot lowers collective to maintain rotor RPM and flares before touchdown.

Tail rotor counters main rotor torque; loss of tail rotor authority causes yaw; fenestron and NOTAR are alternative anti-torque designs.

Settling with power (vortex ring state) occurs with low airspeed, high rate of descent and power applied; recovery is forward cyclic and reduction of power.

Dynamic rollover risk rises with a pivot point on the ground, lateral drift, and full collective; cyclic must be used to counter roll.

Main rotor components: swashplate transfers cyclic and collective inputs; pitch links, dampers and blade grips require inspection for wear and cracks.