Free Module 6 Cheat Sheet 2026: Exam Quick Reference

Ferrous and Non-Ferrous (6.1-6.2)

20%of exam

Steel Codes Steel Heat Treatment Aluminium Alloys Aluminium Tempers Other Metals Metal Testing NDT Method Picker Material Identification Picker

Composites and Non-Metallic (6.3)

22.5%of exam

Fibres and Resins Core and Sandwich Composite Damage Wood and Fabric Plastics and Sealants

Corrosion (6.4)

10%of exam

Corrosion Types Corrosion Control Detection Methods Corrosion Type Picker

Fasteners (6.5)

18.75%of exam

Threads and Bolts Nuts and Locking Solid Rivets Blind and Special Fasteners Locking Device Picker

Pipes, Springs, Bearings (6.6-6.8)

10%of exam

Rigid Pipes Hoses and Fittings Springs Bearing Types Bearing Defects Tube and Hose Picker

Transmissions and Cables (6.9-6.11)

18.75%of exam

Gears and Drives Control Cables Cable Terminals EWIS Wiring Connectors and Bonding

Quick Facts

Module: 6 Materials and Hardware
B1 and B3: 80 questions, 100 minutes
B2 and B2L: 60 questions, 75 minutes
Category A: 52 questions, 65 minutes
Pass mark: 75%, no penalty marking
Format: 3-option multiple choice
Pace: About 75 seconds each
Essays: None in Module 6
Retake: 90 days, 30 retrained
Attempts: Three per 12 months
Validity: 10 years for licence
Syllabus: Applicable 12 June 2024

Temper Codes

T3 cold work, T6 oven, T73 overaged

T3: cold workedT4: naturally agedT6: artificially agedT73: resists stress corrosion

Ferrous vs Non-Ferrous

Ferrous

Iron based
Usually magnetic
Red-brown rust

Non-ferrous

No iron
Non-magnetic
White powder product

Magnet is the first test

NDT Method Picker

Crack in steel part→Magnetic particle(Ferrous only)
Crack in aluminium→Dye penetrant(Surface breaking)
Corrosion in lap joint→Eddy current(Low frequency)
Thickness left after blend→Ultrasonic(Thickness gauge)
Hidden internal structure→Radiography(Sealed areas)
Suspect composite disbond→Tap test(Dull sound)
Water inside honeycomb→Radiography(Shows trapped water)
Enclosed bay access→Borescope(Visual aid)

Steel Codes

SAE 4130: Chrome-moly, weldable thin tubing
SAE 4340: Nickel-chrome-moly, deep hardening
First digit: Main alloying element class
Last two digits: Carbon in hundredths percent
300 series: Austenitic, non-magnetic, not hardenable
321 and 347: Stabilised against weld decay
400 series: Martensitic or ferritic, magnetic
PH grades: Precipitation hardening stainless steels
Ferrite: Body-centred cubic, low temperature
Austenite: Face-centred cubic, above 912 deg C
Martensite: Hard strained quench structure

T3 vs T6

T3

Cold worked
Naturally aged
Sheet and rivets

T6

No cold work
Artificially aged
Higher yield strength

Room ageing vs oven ageing

Material Identification Picker

Magnet sticks strongly→Carbon or alloy steel(Ferromagnetic)
Stainless but non-magnetic→300 series(Austenitic)
Lightest metal, very reactive→Magnesium(Class D fire)
Light, grey, very strong→Titanium(Avoid cadmium)
White powdery corrosion→Aluminium alloy(Oxide product)
Red-brown scale→Steel(Iron oxide)
Gold coloured weave→Aramid(Absorbs moisture)
Black stiff fibres→Carbon(Galvanic risk)

Steel Heat Treatment

Annealing: Furnace cool, softest result
Normalising: Air cool, finer grain
Hardening: Quench to form martensite
Tempering: Reheat, restores some toughness
Eutectoid point: 727 deg C, 0.77% carbon
Carburising: Case hardens low-carbon steel
Nitriding: 500-550 deg C, no quench
Case hardening: Hard skin, tough core
Hydrogen bake: 190-205 deg C after plating
Stress relief: Removes residual working stress

Annealing vs Normalising

Annealing

Furnace cool
Softest, most ductile
Coarse pearlite

Normalising

Still air cool
Tougher and stronger
Finer pearlite

Furnace cool vs air cool

Aluminium Alloys

1xxx: Commercially pure aluminium
2xxx: Copper alloyed, such as 2024
5xxx: Magnesium, good corrosion resistance
6xxx: Magnesium and silicon, 6061
7xxx: Zinc alloyed, such as 7075
2024-T3: Tough, lower wing skins
7075-T6: Strongest, upper wing skins
Alclad: Pure aluminium sacrificial cladding
Clad layer: About 5% each side
Cast codes: Three digits plus decimal
Fusion welding: Not for 2024 or 7075

Aluminium Tempers

F: As fabricated, no control
O: Annealed, softest condition
H: Strain hardened, not heat treated
W: Unstable after solution treatment
T3: Solution, cold worked, naturally aged
T4: Solution treated, naturally aged
T6: Solution treated, artificially aged
T73: Overaged, resists stress corrosion
Quench delay: Risks intergranular corrosion
Natural ageing: Room temperature, over days

Other Metals

Titanium: Strong, light, corrosion resistant
Ti-6Al-4V: Common alpha-beta titanium alloy
Titanium enemies: Chlorinated solvents, cadmium contact
Magnesium: Lightest structural metal, flammable
Magnesium fire: Class D powder only
Inconel: Nickel superalloy, hot sections
Beryllium copper: Non-sparking hand tools
Monel: Nickel-copper, corrosion resistant
Copper: High conductivity, bus bars

Metal Testing

Tensile test: Proof stress, tensile strength, elongation
Brinell: 10 mm ball, 3000 kgf
Rockwell C: Diamond cone, 150 kgf
Vickers: Diamond pyramid indenter
Charpy: Impact energy at notch
Ductile-brittle transition: Steel goes brittle cold
Fatigue limit: Steel has endurance limit
Aluminium fatigue: No true endurance limit
Creep: Slow strain under sustained load
Elastic modulus: Stiffness, about 205 GPa steel

B1 Question Shares

Composites 18, metals 16, fasteners 15

6.3 composites: 186.1-6.2 metals: 166.5 fasteners: 156.9-6.11 drives: 156.4 corrosion: 86.6-6.8 hardware: 8

Thermoset vs Thermoplastic

Thermoset

Cures once
Frozen prepreg storage
Chars if overheated

Thermoplastic

Remelts and reshapes
Ambient storage
Softens with heat

One cure vs re-melt

Fibres and Resins

Carbon fibre: Stiff, conductive, galvanically noble
Glass fibre: Cheaper, insulating, lower stiffness
Aramid fibre: Tough, absorbs water, fuzzes
Boron fibre: Very stiff, hard to cut
Thermoset: Cures once, cannot remelt
Thermoplastic: Remelts and reshapes repeatedly
Matrix job: Transfers shear, protects fibres
Prepreg storage: Frozen at minus 18 deg C
Isolation ply: Glass between carbon and aluminium

Core and Sandwich

Nomex core: Aramid paper honeycomb
Aluminium core: 5052 or 5056 honeycomb
Foam core: Closed cell, easily machined
Balsa core: End-grain wood core
Sandwich action: Skins bend, core shears
Ribbon direction: Cell orientation of core
Water ingress: Adds weight, freezes, disbonds
Potting compound: Fills core at fastenings

Composite Damage

Delamination: Plies separated inside laminate
Disbond: Skin separated from core
BVID: Barely visible impact damage
Resin starvation: Too little resin, dry fibres
Coin tap: Dull note means defect
Scarf ratio: Typically 30:1 to 60:1
Stepped repair: Ply by ply landings
Vacuum bag: About 1 bar consolidation
Hot bonder: Controlled cure with thermocouples
Lightning mesh: Copper or aluminium foil

Wood and Fabric

Sitka spruce: Reference aircraft structural wood
Grain slope: 1 in 15 limit
Moisture content: 8 to 12 percent
Plywood scarf: 1 in 12 steepest
Decay: Any rot means rejection
Compression failure: Buckled fibres across grain
Plywood web: Never replace with solid wood
Fabric limit: 70% of required new strength
Grade A cotton: 80 lb new, 56 minimum
Aluminium dope: Blocks ultraviolet from fabric
Rib stitching: Holds fabric to ribs

Plastics and Sealants

Acrylic: Clear canopies, crazes easily
Polycarbonate: High impact, scratches easily
Transparency cleaning: No alcohol or esters
Thermoplastic: Softens and reforms with heat
Thermosetting plastic: Chars, cannot be reformed
Polysulfide: Two-part fuel tank sealant
Faying seal: Sealant between mating surfaces
Fillet seal: Bead along joint edge
Application life: Working time after mixing

Corrosion Cell

Anode, cathode, electrolyte, path

Break one and it stopsAnode corrodesElectrolyte carries currentPath completes circuit

Galvanic vs Stress Corrosion

Galvanic

Two dissimilar metals
Electrolyte bridge
Anode corrodes away

Stress corrosion

One susceptible alloy
Sustained tensile stress
Brittle branching cracks

Two metals vs one stressed

Corrosion Type Picker

Two dissimilar metals touching→Galvanic(Needs electrolyte)
Layers lifting apart→Exfoliation(Rolled sections)
Cracks under steady tension→Stress corrosion(Susceptible alloy)
Black powder at joint→Fretting(Micro-movement)
Worm tracks under paint→Filiform(High humidity)
Deep local holes→Pitting(Chloride attack)
Attack along grain boundaries→Intergranular(Quench delay)
Sludge in fuel tank→Microbial(Water present)
Trapped moisture in gap→Crevice(Oxygen cell)
Uniform dull etched surface→Surface corrosion(General attack)

Corrosion Types

Surface: General uniform oxide attack
Pitting: Deep local holes, chlorides
Galvanic: Dissimilar metals plus electrolyte
Intergranular: Attack along grain boundaries
Exfoliation: Layers lift in rolled sections
Stress corrosion: Tension plus corrosive environment
Fretting: Micro-movement between clamped parts
Filiform: Worm tracks under paint
Crevice: Trapped moisture, oxygen difference
Microbial: Fuel tank fungus acids
Area effect: Big cathode, small anode

Intergranular vs Exfoliation

Intergranular

Grain boundary attack
Often invisible outside
Heat treatment fault

Exfoliation

Layers lift and flake
Rolled or extruded parts
Visible swelling

Same attack, visible layering

Corrosion Control

Four requirements: Anode, cathode, electrolyte, path
Anodising: Electrolytic thickened oxide film
Alodine: Chromate conversion, self-healing
Cadmium plate: Sacrificial coating on steel
Epoxy primer: Inhibiting pigment under topcoat
CIC: Penetrating water-displacing compound
Banned on aluminium: Steel wool and steel brushes
Blend out: Smooth taper within manual limits
Drain holes: Keep clear of sealant
Humidity threshold: Attack rises above 60%

Detection Methods

Visual: First and primary method
Eddy current: Second layer lap joint
Ultrasonic: Remaining thickness measurement
Radiography: Sealed or hidden structure
Borescope: Enclosed bays and ducts
Blistering: Paint lifted by product
White powder: Aluminium corrosion product
Red-brown scale: Iron oxide on steel
Black powder: Fretting on aluminium joints

Rivet Head Marks

A plain, AD dimple, D dot, DD dash

A: 1100AD: 2117D: 2017DD: 2024B: 5056 cross

AN vs MS

AN

Air Force-Navy standard
Older hardware series
Common general bolts

MS

Military Standard
Newer replacement series
Tighter definition

Older AN, newer MS

Locking Device Picker

Drilled bolt, tension joint→Castellated nut(Cotter pin)
Hot zone near exhaust→All-metal stiffnut(No nylon)
Cool accessible joint→Nylon insert nut(Under 121 deg C)
No access behind panel→Anchor nut(Riveted plate)
Group of drilled fittings→Safety wire(Pull to tighten)
Turnbuckle needs locking→Clip or safety wire(Clip single use)
Shaft end retention→Circlip(No clamp load)
Quick panel removal→Turnlock fastener(Non-structural only)
Permanent high clamp load→Lockbolt(Swaged collar)

Threads and Bolts

UNC: Coarse, soft metals and castings
UNF: Fine, aircraft structural fasteners
Class 3: Tight fit for structure
Pitch: Distance between adjacent threads
Lead: Axial advance per turn
Pitch diameter: Where tooth equals groove
AN bolt diameter: Digit equals 16ths inch
AN bolt dash: Inches then eighths length
Grip length: Match clamped material thickness
Alloy steel head: Raised cross or asterisk
Stainless bolt head: Single raised dash
Aluminium bolt head: Two raised dashes
Close tolerance: Raised triangle, reamed hole
Stud: Coarse into casting, fine outside

Thread Choice

Coarse into soft, fine into steel

UNC: castingsUNF: structureClass 3: tight fit

Castellated vs Self-Locking

Castellated

Cotter pin fitted
Positive mechanical lock
Needs drilled bolt

Self-locking

Prevailing torque
No drilling needed
Limited reuse

Positive lock vs friction

Nuts and Locking

Castellated nut: Cotter pin through drilled bolt
Never slacken: Tighten to align holes
Nylon insert nut: Not above 121 deg C
All-metal stiffnut: For high temperature joints
Thread showing: At least one past nut
Anchor nut: Riveted plate, blind access
Shear nut: Thin nut, shear loads
Safety wire size: 0.032 inch usual minimum
Wire twists: Tight, even, per the manual
Wire direction: Pull toward tightening rotation
Tab washer: Bent against nut flat
Torque rule: Turn the nut, not bolt
Torque adapter: Reduce the wrench setting
Self-tapping screw: Never structural on aircraft

Solid Rivets

A = 1100: Plain head, non-structural
AD = 2117: Dimple head, field standard
D = 2017: Raised dot, higher strength
DD = 2024: Double dash, icebox rivet
B = 5056: Raised cross, for magnesium
M = Monel: Two dimples, stainless structure
Icebox storage: Below minus 18 deg C
Drive window: Minutes after leaving freezer
Shop head: 1.5D wide, 0.5D high
Protrusion: 1.5D of shank before driving
Edge distance: 2D minimum from edge
Rivet pitch: 3D minimum along row
Rivet number: 32nds diameter, 16ths length
MS20470: Universal head solid rivet
Dimple or countersink: Thin sheet must dimple

Bearing Damage

True is a hit, false is a shake

True: shock loadFalse: vibration in transitSpalling: fatigue flakesFluting: electrical arcing

37 vs 45 Degree Flare

37 degree

Aircraft AN standard
Sleeve and nut
Fuel and hydraulics

45 degree

Automotive commercial
Not for aircraft
Crushes AN flare

Never mix flare angles

Tube and Hose Picker

Low pressure fuel line→5052-O aluminium(Soft tube)
High pressure hydraulics→Stainless steel tube(Fire zones too)
Weight critical, high pressure→Titanium tube(3Al-2.5V)
Relative movement between parts→Flexible hose(Allow slack)
Skydrol system hose→Butyl or PTFE(Never Buna-N)
Fuel or oil hose→Buna-N or PTFE(Never butyl)
Soft tube, small diameter→Double flare(37 degrees)
Flare not permitted→Flareless fitting(Bite ferrule)

Rigid Pipes

Tube size: Outside diameter in 16ths
Wall thickness: Quoted in thousandths inch
5052-O: Low pressure fuel lines
6061-T6: Higher strength aluminium lines
Stainless tube: High pressure and fire zones
Titanium tube: Weight critical high pressure
Bend radius: About three times diameter
Flattening limit: Keep 75% of diameter
Never straight: Add bends to absorb flex
Cushioned clamp: Supports line, bonds structure

Brinelling vs Spalling

Brinelling

Indentations in raceway
Shock or press load
Grinding marks remain

Spalling

Metal flakes away
Subsurface fatigue
Gets worse quickly

Dents vs flaking

Hoses and Fittings

AN flare: 37 degree flare angle
Automotive flare: 45 degrees, never mixed
Double flare: Soft tube, 3/8 and smaller
Flareless fitting: Ferrule bites tube wall
Three-piece union: Nut, sleeve and union
Sleeve job: Protects flare from twisting
Lay line: Straight means no twist
Hose slack: 5 to 8 percent
Buna-N: Fuel and oil, not Skydrol
Butyl: Skydrol only, not petroleum
PTFE: Suits all aircraft fluids
Fuel line marking: Red band with stars
Oxygen line marking: Green band with rectangles

Springs

Compression spring: Resists being pushed shorter
Extension spring: Resists being pulled longer
Torsion spring: Resists twist about axis
Leaf spring: Bending strip, high load
Belleville washer: Coned disc, very stiff
Series stack: More deflection, same load
Parallel stack: More load, same deflection
Spring rate: Load per unit deflection
Spring index: Mean diameter over wire
Free length: Checked for permanent set
Shot peening: Compressive skin, longer life
Never stretch: A sagged spring is scrap

Bearing Types

Plain bearing: Sliding contact, high shock
Bushing: Renewable plain bearing liner
Sintered bronze: Oil impregnated, never degrease
Ball bearing: Point contact, high speed
Roller bearing: Line contact, heavy radial
Needle roller: Compact, high radial capacity
Taper roller: Combined radial and thrust
Angular contact: Thrust from one direction
Spherical bearing: Self-aligning rod ends
Cage: Keeps elements evenly spaced
Hydrodynamic film: Oil wedge lifts journal

Bearing Defects

True brinelling: Static shock load indentations
False brinelling: Vibration while not turning
Spalling: Fatigue flaking of raceway
Fluting: Electrical arcing washboard marks
Overheating: Discoloured rings and elements
Contamination: Scratches and dull raceways
Grease fill: 30 to 50 percent
Press rule: Press only the fitted ring
Never spin dry: Compressed air wrecks bearings

Cable Codes

7x19 flies, 7x7 guides, 1x19 stays

7x19: primary controls7x7: secondary runs1x19: rigid ties1/8 in minimum

7x7 vs 7x19

7x7

49 wires total
Less flexible
Secondary and trim runs

7x19

133 wires total
Extra flexible
Primary controls over pulleys

More wires, more flexible

Gears and Drives

Spur gear: Parallel shafts, no thrust
Helical gear: Smoother, creates axial thrust
Double helical: Cancels the axial thrust
Bevel gear: Drives intersecting shafts
Worm drive: High reduction, often self-locking
Rack and pinion: Rotary into linear motion
Epicyclic gear: Sun, planets, ring, carrier
Gear ratio: Driven teeth over driving
Idler gear: Reverses direction, same ratio
Compound train: Multiply the stage ratios
Backlash: Clearance between mating teeth
Pressure angle: Usually 20 degree involute
Tooth contact: Centred oval marking pattern
Chain stretch: Pin and bushing wear
Timing belt: Toothed, positive no-slip drive

Swaged vs Nicopress

Swaged terminal

Machine swaged fitting
Full cable strength
Gauge checked

Nicopress sleeve

Hand tool compression
Field repair method
Sleeve and thimble

Shop terminal vs field loop

Control Cables

7x7: Seven strands of seven
7x19: Extra flexible, primary controls
1x19: Non-flexible, straight tie rods
Galvanised cable: Better bending fatigue life
Stainless cable: Better corrosion, lower fatigue
Minimum size: 1/8 in, primary controls
Measure across: Strand crowns, not valleys
Pre-stretch: Removes constructional stretch first
Proof load: 60% of breaking strength
Reject cable: Popped core or loose strands
Critical fatigue area: One broken wire rejects
Fairlead limit: 3 degrees maximum deflection
Tension regulator: Holds tension despite temperature

Cable Terminals

MS20668: Swaged eye end fitting
MS20667: Swaged fork end fitting
MS20664: Single shank ball end
Go/No-Go gauge: Checks swaged shank size
Witness mark: Paint shows terminal slip
Nicopress sleeve: Field swaged compression sleeve
Turnbuckle threads: Maximum three exposed each end
Left-hand end: Grooved or knurled terminal
Turnbuckle wire: Four wraps around the shank
Locking clip: Single use, never reused
Tensiometer: Riser plus temperature chart
Pulley guard: Stops cable leaving groove

EWIS Wiring

Stranded only: Solid airframe wire banned
AWG: Bigger number, smaller wire
Tin plating: Up to 150 deg C
Silver plating: Up to 200 deg C
Nickel plating: Up to 260 deg C
Red plague: Silver plated copper corrosion
Kapton: Arc tracking risk, legacy
ETFE: Modern non-arc-tracking insulation
Bundle bend radius: 10 times bundle diameter
Coax bend radius: 6 times outside diameter
Route wires: Above fuel and hydraulic lines
Drip loop: Before connectors and bulkheads
Cable tie: Cut flush with proper tool
Voltage drop: Sizes long continuous runs

Connectors and Bonding

MIL-DTL-38999: Standard circular aircraft connector
Scoop proof: Shell reaches pins first
Polarising keys: Prevent cross-mating connectors
Crimp: Gas-tight, vibration resistant joint
Solder: Brittle joint, wicking risk
M22520: Ratcheting calibrated crimp tool
Red tool: Inserts size 20 contacts
White tool: Extracts size 20 contacts
Coax 50 ohm: Aircraft radio transmission line
Coax 75 ohm: Video, not aircraft radio
Bond resistance: Typically under 0.003 ohm
Screen earthing: One end only, short
Ignition screen: Suppresses interference and flashover

Common Traps

Tempering vs annealing

Tempering follows a quench ≠ Annealing softens from scratch

Galvanic vs intergranular

Galvanic needs two metals ≠ Intergranular follows heat treatment

Hardness vs strength

Hardness resists indentation ≠ Strength resists breaking load

Rivet AD vs DD

AD is 2117 dimple ≠ DD is 2024 icebox

Flare angle mix

Aircraft flares 37 degrees ≠ Automotive flares 45 degrees

Idler gear myth

Idler reverses direction ≠ Idler keeps the ratio

MPI on light alloy

Magnetic particle needs iron ≠ Aluminium needs eddy current

Turnbuckle threads

Three threads may show ≠ More means weak engagement

Nylon nut heat

Nylon fails above 121 deg C ≠ All-metal nut for heat

Skydrol hose liner

Butyl suits Skydrol ≠ Buna-N swells in Skydrol

Stop-drilling is not repair

Stop-drill halts the crack ≠ Reinforcement restores the strength

Last Minute

1.B1: 80 questions in 100 minutes
2.Pass 75%, no penalty marking
3.Composites 22.5% is the heaviest band
4.T3 cold worked; T6 oven aged
5.AD 2117 dimple; DD 2024 icebox
6.Shop head 1.5D wide, 0.5D high
7.Edge distance 2D; rivet pitch 3D
8.Galvanic needs two metals plus electrolyte
9.Stress corrosion needs sustained tension
10.Magnetic particle works on steel only
11.Aircraft flare angle is 37 degrees
12.7x19 cable for primary controls
13.Turnbuckle: three threads maximum showing
14.Nylon nut limit 121 deg C
15.Gear ratio is driven over driving
16.Wire bundle bend: 10 times diameter
17.Press only on the fitted ring
18.Never stretch a sagged spring

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