Iran CAO Part-66 AMT Theory key terms

A quantity that has both magnitude and direction, such as velocity or force. It is represented by an arrow whose length gives the size and whose orientation gives the direction, and vectors add by geometric or component methods.

The single vector that produces the same overall effect as two or more combined vectors. It is found by resolving each vector into perpendicular components, summing the components, then recombining them.

The turning effect of a force about a point, equal to force multiplied by the perpendicular distance from the point to the force's line of action. Moments are balanced in equilibrium problems such as control surface hinge calculations.

The state in which all forces and moments acting on a body cancel, so it has no linear or angular acceleration. In static aircraft problems this means summed forces and summed moments both equal zero.

Internal force per unit cross-sectional area within a loaded material, expressed in pascals or newtons per square millimetre. Normal stress may be tensile or compressive, while shear stress acts parallel to the surface.

The fractional change in length of a material under load, a dimensionless ratio of extension to original length. Strain is proportional to stress within the elastic range, as described by Hooke's law.

The ratio of tensile stress to tensile strain in the linear elastic region of a material, a measure of stiffness. A higher value means the material deflects less under the same applied stress.

Progressive cracking of a material caused by repeated or fluctuating loads at stress levels below its static strength. It starts at stress raisers such as scratches, rivet holes, or sharp corners and grows until final failure.

The maximum load an aircraft structure is designed to tolerate, normally 1.5 times the limit load. The structure may suffer permanent deformation at ultimate load but must not fail catastrophically.

The greatest load expected in service, which the structure must withstand without permanent deformation or harmful residual effects. It is multiplied by the factor of safety to give the ultimate load.

A multiplier applied to the limit load to obtain the ultimate load, conventionally 1.5 in civil aircraft structural design. It covers uncertainties in loads, material properties, and analysis methods.

The relationship stating that current through a conductor is directly proportional to voltage across it and inversely proportional to resistance, written V equals I times R. It applies to resistive circuits at constant temperature.

Two circuit rules: the sum of currents entering a junction equals the sum leaving it, and the algebraic sum of voltages around any closed loop is zero. They allow analysis of complex series and parallel networks.

The total opposition to alternating current in a circuit, combining resistance with inductive and capacitive reactance as a complex quantity. It determines current magnitude and phase relative to applied voltage.

The cosine of the phase angle between voltage and current in an AC circuit, expressing the fraction of apparent power that does real work. A low value indicates a large reactive component.

A two-terminal semiconductor device that conducts readily in one direction and blocks the other, used for rectification and protection. Its forward voltage drop is about 0.7 volts for silicon.

A three-terminal semiconductor device used for amplification or switching, in which a small control current or voltage governs a larger main current. Bipolar and field-effect types are common in avionics circuits.

A high-gain differential amplifier integrated circuit used with external feedback components to perform amplification, filtering, summing, and comparison functions in analogue avionic signal conditioning.

A circuit arrangement of diodes that converts alternating current into pulsating direct current. Half-wave types use one diode, while full-wave bridge types use four to use both halves of the cycle.

A device that samples a continuously varying voltage and converts each sample into a binary number for processing by digital systems. Resolution is given in bits and accuracy depends on reference stability.

A circuit that converts a binary digital word into a proportional analogue voltage or current, used to drive indicators, actuators, or analogue transmitters from digital computers.

A widely used avionics digital data bus standard that transmits 32-bit words over a twisted shielded pair using bipolar return-to-zero signalling, typically at 12.5 or 100 kilobits per second.

A simple error-detection method in which an extra bit is added so the total number of ones is always odd or even. It detects single-bit errors but cannot correct them.

A shared digital pathway, with defined protocol and physical medium, over which line-replaceable units exchange data. Examples include ARINC 429, ARINC 629, and MIL-STD-1553.

For steady, incompressible, frictionless flow along a streamline, the sum of static pressure, dynamic pressure, and potential energy per unit volume remains constant. It explains lift generation and venturi behaviour.

The angle between the wing chord line and the relative airflow approaching it. Increasing it raises lift up to the critical angle, beyond which the airflow separates and the wing stalls.

Loss of lift caused by separation of airflow from the upper wing surface when the critical angle of attack is exceeded. It depends on angle of attack, not directly on airspeed, and is preceded by buffet.

The point on an aerofoil where the resultant aerodynamic force acts. Its position moves forward as angle of attack increases, which affects pitching moments and control balance.

In forward helicopter flight, the advancing blade meets higher relative airflow than the retreating blade, producing unequal lift. Blade flapping and cyclic pitch changes equalise lift across the disc.

A helicopter condition in which the retreating blade, exposed to low relative airflow at high forward speed or high load, exceeds its critical angle of attack and stalls, causing pitch-up and vibration.

The extra lift a helicopter rotor produces once it moves out of its own downwash into undisturbed air, typically above about 15 to 20 knots. It improves efficiency and reduces power required.

Electrochemical deterioration of a metal through reaction with its environment, appearing as surface pitting, exfoliation, or galvanic attack between dissimilar metals. Inspection and protective treatments limit its progress.

Corrosion caused when two dissimilar metals in electrical contact are exposed to an electrolyte, the more anodic metal dissolving. It is prevented by isolating the metals or choosing compatible pairs.

The rotational equivalent of force, calculated as force multiplied by lever arm, used to specify fastener tightening. Correct torque values ensure joints carry design loads without overstressing or loosening.

The fraction of a repeating period during which a device or signal is active, usually expressed as a percentage. It influences heating in motors and the average value of pulsed electrical signals.

The rate of doing work or transferring energy, measured in watts. In electrical circuits it equals voltage multiplied by current for direct current, or voltage times current times power factor for alternating current.

An unintended action or omission by a person that deviates from intended or required behaviour. In maintenance it is classified as slip, lapse, mistake, or violation and is managed through procedures and error-capturing systems.

A set of twelve human-factor precursors commonly linked to maintenance errors, including fatigue, complacency, pressure, distraction, lack of communication, and lack of knowledge. Recognising them supports mitigation before an error occurs.

A person's accurate perception and understanding of what is happening around them and what is likely to happen next. Loss of it contributes to lapses in inspection, tool control, and task sequencing.

A mandatory instruction issued by a civil aviation authority to correct an unsafe condition in aircraft, engines, or components. Compliance is required within a stated time and is recorded in the aircraft logbooks.

The set of processes ensuring an aircraft remains compliant with its type design and safe throughout its service life. It covers maintenance programmes, modifications, defect control, and record keeping.

A certification, signed by authorised personnel after maintenance, confirming that the work has been completed satisfactorily and the aircraft or component is serviceable for the intended operation.

A document issued by a design or production organisation recommending inspection, modification, or replacement of a product. It is advisory unless made mandatory by an airworthiness directive or operator requirement.