EASA Module 7 key terms

Any loose object, debris or tool left in or around an aircraft that could damage equipment, jam controls or be drawn into an engine. Preventing FOD is a continuous housekeeping duty for everyone working on the aircraft.

Items worn or used by a person to reduce the risk of injury, such as eye protection, gloves, hearing protection and breathing masks. The selection depends on the hazards identified for the task.

Document supplied with a hazardous substance that describes its hazards, safe handling, first aid, storage and disposal requirements. It must be available to anyone who uses or stores the product.

Procedure for isolating an energy source, such as electrical power or hydraulic pressure, before work starts. The isolator is locked and tagged so that only the person who applied it can restore the supply.

A turning or twisting moment applied to a fastener, measured in newton metres or pound-inches. Correct torque produces the clamping load the joint designer intended without over-stressing the bolt or surrounding structure.

Stainless steel wire threaded through drilled heads of adjacent fasteners and twisted so they cannot rotate loose. It is installed so that any tendency of a fastener to loosen tightens the wire.

Precision instrument with a calibrated screw that measures outside dimensions to hundredths or thousandths of a millimetre. The reading is taken from the barrel and thimble scales after the spindle touches the part.

Measuring tool with fixed and sliding jaws plus a vernier scale, used for external, internal and depth measurements. It typically reads to about 0.02 mm and must be checked against zero before use.

Instrument with a spring-loaded plunger and a dial that shows small movements or deflections. It is used to check run-out, alignment, backlash and flatness, often mounted on a magnetic stand.

Wrench that indicates or limits the torque applied to a fastener. It must be calibrated at defined intervals, set to the specified value before use, and wound back to zero for storage.

Drawing method that shows a three-dimensional object as separate views, usually front, top and side, each seen at right angles. It is the standard way of defining aircraft parts on engineering drawings.

Area of an engineering drawing that gives the drawing number, part name, revision status, scale, sheet number and approval signatures. It identifies which version of the drawing is current.

List on or with a drawing giving every part, material and standard hardware needed to build or repair the assembly, with part numbers and quantities. It is used for ordering and for checking completeness.

Industry standard that divides an aircraft into numbered chapters by system, such as chapter 24 for electrical power. Maintenance manuals, parts catalogues and task cards are organised using these chapter numbers.

Permitted total variation in a dimension, being the difference between the upper and lower limits. Parts made within tolerance will assemble and function as intended, so tolerance is not the same as a wear limit.

A fit in which the shaft is always smaller than the hole, leaving a gap between the parts. It allows relative movement or easy assembly, and the size of the gap depends on the selected tolerance grades.

A fit in which the shaft is larger than the hole, so assembly requires force, heating the part with the hole or cooling the shaft. The resulting grip transmits load and resists vibration and rotation.

Electrical Wiring Interconnection System: the complete set of wires, connectors, terminals, splices, shielding and associated hardware in an aircraft. It is treated as a system in its own right with specific inspection and maintenance requirements.

Electrical connection made between metallic structure and equipment, or between structural parts, to provide a low-resistance path for current. It protects against lightning, static and fault currents and prevents sparking.

Method of attaching a terminal or splice to a wire by mechanically deforming it with a crimping tool. A correct crimp uses the specified tool and die and is checked by pull test and inspection.

Number that identifies the cross-sectional area of an electrical wire, commonly given in the American Wire Gauge system. The larger the gauge number, the smaller the wire and the lower its current capacity.

Practice of routing power, signal and sensitive wiring separately, using physical spacing or barriers, so that electromagnetic interference and fault damage cannot pass from one circuit to another.

Distance between the centres of adjacent rivets in a row. It is specified by the designer, usually as a multiple of rivet diameter, and affects the strength and fatigue life of the joint.

Adjustable barrel fitted in a control cable run, with right- and left-hand threaded ends, used to set cable tension and rigging. After adjustment it is secured by lockwire or check nuts.

Permanent method of attaching a terminal to a cable or a fitting to a hose by pressing or rolling the metal onto it with a die. The completed swage is inspected and proof-loaded to confirm it holds.

Axial or radial load deliberately applied to a bearing assembly to remove internal clearance and keep the rolling elements loaded. Correct preload prevents skidding and vibration; too much causes overheating.

Forming a cone on the end of a rigid tube so that a mating sleeve and nut can clamp it against a fitting seat. The flare angle and surface finish must be correct to seal under pressure.

Joining process in which a filler metal melts above 450 degrees Celsius but below the melting point of the parent metals and is drawn into the joint by capillary action. The parts themselves do not melt.

Joining process using a filler metal that melts below 450 degrees Celsius, used mainly for electrical connections. The joint relies on clean, fluxed surfaces and good wetting rather than on melting the base metal.

Heat treatment in which metal is heated and then cooled slowly to soften it, relieve internal stress and restore ductility. It is often required after welding or cold working before further forming.

Non-destructive method for finding surface cracks in non-porous materials. Penetrant is applied, excess is removed, and developer draws penetrant out of defects so they appear as visible indications.

Point at which the whole weight of the aircraft is considered to act. Its position must remain within the certified forward and aft limits for the aircraft to be controllable and structurally loaded as designed.

Product of a weight and its distance from a reference point called the datum, used in weight and balance calculations. Summing moments and dividing by total weight gives the centre of gravity position.

Raising the aircraft on purpose-made jacks at the specified jacking points, following the maintenance manual. The aircraft must be on level ground, chocked, and correctly supported before work underneath begins.

Securing an aircraft on the ground against wind using tie-downs at the specified points, with controls locked and covers fitted as instructed. The procedure protects the aircraft from unwanted movement and damage.

Mandatory requirement issued by the airworthiness authority to correct an unsafe condition in a type-certificated product. It must be complied with within the stated time and the action recorded in the aircraft documents.

Document from the manufacturer giving a recommended inspection, modification or maintenance action, which is usually not mandatory on its own. It becomes mandatory when an airworthiness directive refers to it.

Independent second inspection of a critical task, such as a flight control connection or assembly, carried out by an authorised person other than the one who did the work, and recorded as such.

Setting of control surfaces, linkages and systems to the specified travels, clearances and tensions so the aircraft responds correctly. It follows defined checks and is usually confirmed by a duplicate inspection.

Check that a system or component operates as intended through its full range after maintenance, following the maintenance manual procedures, without necessarily measuring its performance in detail.