Aviation Maintenance Terms
Blade
One arm of a propeller from the hub to tip.
Blade angle
An angle between the chord line of a propeller blade section and a plane perpendicular to the axis of propeller rotation.
Blade station
See Stations.
Blade track
The path established by the tip of each blade as it passes a fixed point in rotation.
Chord
The distance from the blade leading edge to the trailing edge.
Chord line
A straight line drawn between the leading and trailing edges of the blade.
Corrosion
Deterioration of a metal because of reaction with its environment. For further references see AC 43-4, Corrosion Control for Aircraft.
Corrosion, intergranular
Intergranular corrosion occurs in the grain boundaries of some alloys of aluminum. The presence of intergranular corrosion may be the result of fatigue, stress, or the continued presence of moisture such as under a decal, or in a fastener hole. Sometimes called exfoliation corrosion, when it occurs in forgings, extrusions or rolled sheets.
Corrosion, pitting
Visible cavities extending inward from the metal surface due to chemical or electro-chemical action.
Corrosion, surface
Surface loss of metal due to chemical or electro-chemical action. On polished surfaces begins as a dulling of surface, soon becoming frosted, followed by widespread pitting.
Crack
A physical opening or fissure within the body of a material. May be either internal within the material or at the surface (surface breaking). On a propeller, cracks can be started by cuts, nicks, or corrosion.
Cut
A deep, long, narrow fissure usually caused by a sharp object.
Debond/Disbond
An adhesive or cohesive failure or separation along a bonded interface between two or more surfaces.
Delamination
Separation between adjacent layers of a laminate.
Dent
A depression in the blade as the result of impact from a blunt object.
Depression
Concave surface deformation.
Diameter, propeller
The diameter of the circle circumscribed by the blade tips.
Erosion
Surface removal of material by mechanical action of grit, sand, water, etc., usually present on the leading edge close to the tip.
Face surface
Flat, or very slightly curved, side of the propeller blade against which the relatively higher pressure acts to produce thrust when the propeller is rotated.
Gouge
A deep groove on a blade formed by a heavy pressure contact with a solid object.
Horizontal balance
The blade balance process that locates the center of blade mass along the radial direction to reduce unbalance of an assembled propeller.
Hub
Center section of the propeller that carries the blades and is attached to the engine shaft.
Impact damage
Damage (visible or not) resulting from a blade striking or being struck, while in flight or on the ground, by an object such as a snow bank, runway light, maintenance stand, birds, etc.
Inclusion
Material foreign to base metal but contained in it.
Leading edge
The edge of the blade that leads the direction of rotation and first encounters the air.
Lightning strikes
Damage to blades caused by lightning usually manifested by localized burning, discoloration, melted metal, and/or pits.
Nick
A sharp notch-like displacement of metal usually found on leading and trailing edges.
Overhaul
Complete teardown and reassembly associated with major repair or maintenance. The terms overhaul and reconditioning are synonymous for fixed pitch propellers.
Pitch
The theoretical distance that the propeller blade reference station would move forward if it were moving along a helix with an angle equal to the blade section angle.
Pitting
Small irregularly shaped cavities from which material has been removed by erosion or corrosion. Corrosive pitting is usually accompanied by a deposit such as rust, a corrosion byproduct, formed by a corrosive agent on the base metal.
Propeller
A device for propelling an aircraft that has blades on an engine-driven shaft and that, when rotated, produces by its action on the air, a thrust approximately perpendicular to its plane of rotation. It includes associated control components normally supplied by its manufacturer.
Propeller, Constant speed
A propeller in which a governor is used to automatically provide constant revolutions per minute as the pilot selects the propeller pitch setting.
Propeller, Controllable pitch
A propeller with blades that may be altered continuously to any desired angle during flight.
Propeller, Fixed-Pitch
A one-piece propeller with fixed blade angles.
Propeller, Full feathering
A propeller with blades that can be rotated to a high positive blade angle to stop rotation (windmilling). This feature is common on multi-engine aircraft, because it allows an engine to be shut down and rotation stopped to reduce drag and asymmetric control forces.
Propeller, reversing
A propeller in which blades can be rotated to a “negative” blade angle where they will provide a rearward thrust to slow down, stop, or move the aircraft backward.
Reconditioning
The repair of major or minor blade damage caused by erosion or striking small objects during normal operation. Reconditioning consists of penetrant inspection, refinishing, and re-balancing. It is accomplished on an irregular basis as necessary and required.
Repair
The correction, on an irregular basis as necessary, of minor or major damage caused by a physical mishap. The amount, degree, and extent of damage determine whether or not the propeller can be repaired as a minor repair in the field by a mechanic.
Score
Groove-like indentations from rubbing by a hard, rough surface. See gouge.
Shank
The portion of the blade from the butt face to the first blade station.
Stations
Locations perpendicular to the blade center line at which dimensions are checked.
Tip
The portion of the blade outermost from the axis of propeller rotation.
Tracking
See blade track.
Trailing edge
The rear edge of the blade where the air leaves the blade.
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