When you are out on the ramp inspecting an engine or completing a logbook entry before departure, accuracy is everything. Using the precise terminology found in the Standard Practices Manual (AMM 70-00-00) ensures that tech records, oncoming shifts, and downstream repair shops know exactly what was observed.
This quick-reference guide breaks down universal engine orientation rules and organizes all standard defect terms into logical, highly scannable categories for training and educational purposes.
1. Ground Rules: Engine Orientation & Layout
Before documenting an engine observation, ensure your spatial and structural references match the universal AMM coordinate system:
- Engine Attitude: Directional and clock references apply to the engine in a horizontal position.
- Primary Viewpoint: Always view the engine from the rear, looking forward (towards the fan).
- The Base (6 O’Clock): The engine accessories section is always considered the absolute bottom.
- Circumferential Numbering: When components or struts are numbered in a circumferential direction, the No. 1 position is at 12 o’clock, or immediately clockwise from 12 o’clock.
- The Clock Rule: All remaining structural positions, struts, or component sequences increase arithmetically in a clockwise direction.
2. Standard Risk Annotations
The manual explicitly defines procedural risk levels using these three classifications:
- ⚠️ WARNING: Warnings call attention to methods, procedures, or limits which, if not precisely followed, pose a particular risk of injury or death to persons.
- 🛑 CAUTION: Cautions call attention to methods and procedures which, if not precisely followed, pose a particular risk of equipment damage.
- 💡 NOTE: Notes call attention to methods which make the job easier, or provide supplementary or explanatory information.
3. The Complete Defect Directory
Category A: Surface Friction, Wear & Material Removal
Use these terms when components are rubbing, scraping, or losing material due to mechanical operational motion.
| Term | Official AMM Definition | Associated Cross-Reference Terms |
| Burnishing | Smoothing of a metal surface by mechanical action, but without a loss of material. Generally found on plain bearing surface. Surface discoloration is sometimes visible around the outer edges. Normal burnishing from operational service is not detrimental if the coverage approximates the carrying load and there is no evidence of burns. | Rub, Wear |
| Chafing | Cross-reference entry. | See “Gall” or “Scratch” |
| Erosion | Gradual wearing away of a surface caused by a fluid (gas or liquid) flowing over the surface. Wear is generally caused by fine particles of foreign material entrained in hot engine gases flowing at a high velocity. | None listed |
| Flaking | Cross-reference entry. | See “Spalling” |
| Fretting | Wearing away by low-amplitude rubbing against another metal (generally associated with press fit or close fitting parts). | Wear, Galling |
| Galling | A defect caused by the movement of 2 surfaces in contact with each other. In most cases, an accumulation of foreign material is deposited on the parent material. | Pickup |
| Gouge | A wide, rough scratch or group of scratches, usually with one or more sharply incised corners, and frequently accompanied by deformation or removal of parent material. | None listed |
| Groove | A long, narrow, continuous depression caused by pressure of a moving surface in contact with the parent material. | If depression is shallow and smooth, see “Wear”; if depression is sharp, see “Scratch”. |
| Rub | A surface depression or displacement caused by two surfaces moving while in contact with each other. | If impression is shallow and smooth, see “Wear”; if impression is sharp, see “Scratch”. |
| Scratch | A long, narrow, sharp-cornered impression caused by the movement of a sharp object across the surface of the parent material. | Abrasion, Chafe, Furrow, Groove, Score |
| Wear | Relatively slow removal of parent material in the process of operation (not always visible to the naked eye). | Abrasion, Attrition, Brinnelled, Chafed, Chattering, Erosion, Fraying, Fretting, Friction, Galling, Glazing, Groove, Interference, Oxidation, Roughness, Rubbed, Scarfed, Scuffed, Uneven, Weak |
Category B: Structural Contours & Shape Alterations
Use these terms when a part has buckled, bent, shifted, or deformed from its original blueprint layout.
- Buckle: A large-scale deformation of the original contour of a part, usually caused by pressure or impact from a foreign object, structural stresses, excessive localized heating, high-pressure differentials, or any combinations of these.
- Associated Terms: Ballooning, Bend, Bulge, Crease, Curl, Dent (not to be confused with small-area defect in heavy material), Depression, Distortion, Elongation, Fold, Indentation, Kink, Protrusion (hollow), Rupture (result of excessive buckling), Uneven, Warpage, Wrinkle.
- Creep: Gradual continuous distortion or plastic flow under constant stress. (Associated terms: None).
- Deformation: Any alteration or change of shape, dimension or configuration resulting from stress or damage.
- Associated Terms: Bend, Creep, Distortion.
- Dent: A completely smooth surface depression caused by pressure or impact from a smooth, rounded foreign object. The parent material is displaced, but none is separated. (Associated terms: Peen).
- Distortion: Any twisting, bending or permanent strain that results in misalignment or change of shape. (Associated terms: Bend, Deformation).
- High spots: Local distortions. (Associated terms: Blister, Buckle, Bubble, Out-of-round).
- High metal: Displaced metal adjacent to a defect such as a scratch, nick or gouge, which is raised above the surrounding. (Associated terms: Burr).
- Oil-canning (Snapping action): Snapping or popping displacement of sheet metal when restrained at its edges like a diaphragm, wall, or bottom of an oil can. (Associated terms: Buckling).
- Pinched: Distortion of one or more surfaces of the parent material, caused by pressure.
- Associated Terms: Bound, Bound (noted duplicate in manual), Compressed, Flattened, Seized, Smashed (without separation into pieces), Squashed, Squeezed.
Category C: Material Breaks, Separations & Cracks
Use these terms when a component’s physical parent material or internal structural bonding is fractured, cut, or split apart.
- Burr: A rough edge or a sharp protrusion on the edge or surface of the parent material. (Associated terms: None).
- Chip: A breaking away of the edge of the parent material, usually caused by heavy impact from a foreign object.
- Associated Terms: Break, Nick (similar to Chip, but no parent material is removed), Notched, Spalling (usually a broken-away flat surface).
- Crack: A parting or discontinuity in the parent material.
- Associated Terms: Break, Cold shut (castings), Crater (castings), Fatigue damage, Fissure, Fracture, Lap (forgings), Rupture, Seam, Separation, Slit, Tear.
- Crazing: A mesh of minute hairline cracks found in glazed or baked-on coated surfaces, generally caused by temperature change or by deformation of parent metal. Cracks do not penetrate into parent metal. (Associated terms: None).
- Discontinuity: An interruption in the normal physical structure or configuration of a part. (Associated terms: Crack, Seam, Cold shut, Lap).
- Fatigue: The progressive fracture of a material under cyclic stress loading. (Associated terms: Crystallization, Fretting, Flaking).
- Nick: A surface impression with sharp corners or bottom, usually caused by pressure or impact from a sharp-edged object. The parent material is displaced, but usually none is separated. (Associated terms: Chip, Dent, Notch).
- Spalling: Cracking off or flaking off of small particles of metal from the surface, usually in thin layers or localized spots. (Associated terms: Flaking, Fretting, Galling).
- Tear: A physical separation by tearing, pulpulling (verbatim text) apart by force, or wrenching of metal. (Associated terms: None).
Category D: Thermal, Chemical & Environmental Damage
Use these terms when extreme localized temperatures, atmospheric exposure, or chemical interaction has broken down the material surface.
- Blister: A raised portion of a surface caused by separation of the outer layers of the parent material or of a coating applied to it. (Associated terms: Bubble, Flaking, Oxide Formation, Peeling, Scale, Slag inclusion (weld))
- Brittle: A change in the elasticity or resilience of the parent material usually caused by aging, extreme cold, chemical action, or cold-working. (Associated terms: Cold worked hard (like an old O-ring))
- Burn: A rapid, destructive, oxidizing action, usually caused by higher temperatures than the parent material can withstand. Change in color appearance often indicates this condition.
- Associated Terms: Burn-out (missing piece), Erosion, Corrosion, Guttered, Heat-check, Heat deterioration, Hole (burn), Hot spot, Overheated, Oxidiation (verbatim text).
- Corrosion: A mass of small pits which cumulatively create a large, shallow cavity (usually rough in the surface of the parent material). (Associated terms: Pit)
- Pit: A minute depression or cavity having no sharp, high-stress corners in the surface of the material. Pits are usually caused by chemical reaction (rusting, chemical corrosion). (Associated terms: Corrosion, Crater, Electrolytic cavity, Inclusion, Perforation, Pinholes, Pock-marked)
- Porosity: Areas containing numerous pits or pinholes. (Associated terms: Pit, Pinholes)
- Scale: A layer of metallic oxides formed by chemical action of oxygen on the exposed surface of the metal, usually while hot. (Associated terms: Burn)
- Varnish film: A hard surface-film of partially carbonized hydrocarbon, such as oil, which is built up when the part is heated to or above the breakdown-point of the fluid. (Associated terms: Banded, Discolored, Oxidized, Stained)
Category E: Mechanical Assembly & System Integrity
Use these terms during dynamic engine troubleshooting, fitment evaluation, and systemic component checking.
- Deviation: Any condition that causes a part to differ from the manufacturer’s blueprint. (Associated terms: Damage, Defect, Flaw, Imperfection, Irregularity)
- Imbalance: The state of being out-of-balance. Unequal distribution of weight about the axis of rotation, which usually results in vibration. (Associated terms: None).
- Inclusion: Foreign material embedded in metal during solidification, or formed by subsequent reaction of the solid metal. (Associated terms: None).
- Indication: The visible evidence that a material defect exists, even though the defect itself may not be visible to the naked eye. (Associated terms: None).
- Looseness: Abnormal movement of a part, or insufficient securing of a part.
- Associated Terms: Backed out, Excessive play, Excessive back-lash, Insufficient torque, Shaky, Sloppy, Unbottomed, Unpinned, Unwired.
- Misalignment: A mismatching or malformation of any part which either prevents perfect assembly or results in faulty operation and/or ultimate failure. (Associated terms: Eccentric, Out-of-round, Out-of-square, Mismatched, Unmatched)
- Noise: An abnormal sound involving moving parts, usually an increase in volume or a change of pitch.
- Associated Terms: Bumps (sound), Chatters, Clicks, Grates (usually gears), Grinds, Hums, Rattles, Rubs, Scrapes (sound), Screeches, Thumps, Whistles.
- Obstruction: Prevention of free flow of a fluid (air, oil, fuel, water) because of foreign material in the flowpath or malformation of the part. (Associated terms: Clogged, Contaminated, Plugged, Restricted)
- Pickup: Transfer of one material into or onto the surface of another in contact with it, usually as a result of friction-heating. (Associated terms: Burr, Gall, Imbedment, Inclusion, Pile-up, Protrusion, Metallization)
- Seizure: A welding or binding of faces which prevent further movement. (Associated terms: Bound up, Frozen, Tight, Wedged, Welded (without external heating))
- Shingling: A condition when one fan blade mid-span shroud moves over the other (usually when something hits the fan). It is called shingled when fan blade mid-span shroud stays overlapped on the other. The condition can also occur to the blade tip shrouds on the LPT rotor (Stg. 3 and 4). The condition on the LPT is usually caused by a loss of pre-twist, too much radial movement, etc. (Associated terms: Wedged, Bound up, Shingled)
- Unbalance: The act of putting a balanced component out of balance. Usually “imbalance” is meant. (Associated terms: None).
4. Universal Measurement & Baseline Terms
The manual includes two specific definitions that act as structural baselines for evaluating component damage limits:
- No apparent Depth: Term used to describe surface defects that can be seen but not felt with fingernail or scriberpoint.
- Parent Metal: All material in a single part except the weld, braze filler, or heat-affected zone (within 1/8 inch (3.175 mm) of the fusion line).
⚠️ Educational Use Only: This guide (optimized for the Airbus A320neo / CFM LEAP-1A) is for general educational and quick-reference purposes only. It is designed to help aviation students and technicians familiarize themselves with standard industry definitions and engineering concepts. Never use this web reference as a substitute for live, approved technical data. Always consult the current, legally effective Aircraft Maintenance Manual (AMM) and specific task revisions for the exact tail number you are working on before performing or signing off on any aircraft maintenance actions.
