Part-66 Module 6 questions are about the stuff aircraft are built from: the steels, aluminium alloys and composites in the structure, the corrosion that attacks them, and the hardware that holds everything together. For B1 candidates it is one of the longest papers in the first ten modules. This guide gives the paper size for every category under EASA and UK CAA rules, walks through all eleven sub-modules with the details examiners test, and sets out a study plan.
Part-66 Prep is an independent study aid, not EASA, the UK CAA or a Part-147 organisation. The syllabus is Appendix I and the paper sizes are in Appendix II to Part-66, in Regulation (EU) No 1321/2014 as amended by Regulation (EU) 2023/989 for the EU, and in UK Part-66 for the UK. The Part-66 modules guide shows where Module 6 fits.
Part-66 Module 6 exam size by category
| Category | EASA questions / minutes | UK CAA questions / minutes | Correct answers needed (75%) |
|---|---|---|---|
| A (A1 to A4) | 52 / 65 | 52 / 65 | 39 |
| B1.1, B1.2, B1.3 | 80 / 100 | 72 / 90 | 60 (EASA) / 54 (UK) |
| B2 and B2L | 60 / 75 | 60 / 75 | 45 |
| B3 | 80 / 100 | 60 / 75 | 60 (EASA) / 45 (UK) |
There are no essays in Module 6. Under EASA rules a paper over 90 minutes may be split into two partial exams, each with a number of questions that is a multiple of four and each passed at 75%, so a B1 or B3 candidate may meet Module 6 as two 40-question sittings. Ask your exam centre how it runs the paper. UK Part-66 has no general partial-exam rule.
Key fact: The UK B3 paper is 20 questions shorter than the EASA one, the largest gap in Module 6. The content is the same; the UK simply samples fewer questions from it.
Depth by category
Module 6 is a B1 module at heart. B1 and B3 sit most topics at level 2, and corrosion types at level 3, the deepest knowledge level the syllabus uses. B2 sits most topics at level 1 or 2 and skips some B1 material entirely: defect detection in composites, wooden structures and fabric covering. Category A sits a lighter version and does not sit springs, materials testing or repair procedures.
| Sub-module | A | B1 / B3 | B2 / B2L |
|---|---|---|---|
| 6.1 Ferrous materials (alloy steels; testing; repair and inspection) | 1 / — / — | 2 / 1 / 2 | 1 / 1 / 1 |
| 6.2 Non-ferrous materials (same three parts) | 1 / — / — | 2 / 1 / 2 | 1 / 1 / 1 |
| 6.3.1 Composites and non-metallics (characteristics; defects; repair) | 1 / 1 / — | 2 / 2 / 2 | 2 / — / 1 |
| 6.3.2 Wooden structures | 1 | 1 | — |
| 6.3.3 Fabric covering | — | 1 | — |
| 6.4 Corrosion (chemistry; types) | 1 / 2 | 1 / 3 | 1 / 2 |
| 6.5 Fasteners (threads, bolts, locking devices; rivets) | 2 / 1 | 2 / 2 | 2 / 1 |
| 6.6 Pipes and unions | 2 | 2 | 2 / 1 |
| 6.7 Springs | — | 2 | 1 |
| 6.8 Bearings | 1 | 2 | 2 |
| 6.9 Transmissions | 1 | 2 | 2 |
| 6.10 Control cables | 1 | 2 | 1 |
| 6.11 Electrical cables and connectors | 1 | 2 | 2 |
Practise the paper for your category: B1.1 Module 6 paper 1, B2 Module 6 paper 1, or the hubs for category A and B3.
Module 6 sub-modules: what examiners test
6.1 Ferrous materials
Alloy steels used in aircraft, their properties and identification, heat treatment (hardening, tempering, annealing, normalising, case hardening), testing for hardness, tensile strength, fatigue strength and impact resistance, and repair and inspection.
What examiners like: what each heat treatment does, which alloying element gives which property (chromium for corrosion resistance, nickel for toughness, molybdenum for strength at temperature), and which hardness test uses which indenter. Trap: annealing softens and relieves stress; tempering follows hardening to reduce brittleness. Our free ferrous materials note has a heat-treatment table.
6.2 Non-ferrous materials
Aluminium, titanium, magnesium, copper and nickel alloys, their identification and heat treatment, testing, and repair and inspection.
What examiners like: the aluminium alloy series by main alloying element (2xxx copper, 7xxx zinc and so on), what solution treatment and age hardening achieve, why clad aluminium has a pure aluminium surface layer, and the temper designations. Trap: magnesium alloys are light but highly reactive and a fire risk when machined. See the non-ferrous materials note.
6.3 Composite and non-metallic materials
Fibre-reinforced composites (glass, carbon, aramid), matrices, sandwich and honeycomb structures, sealants and bonding agents, defect detection, repair principles, and for B1 and A also wooden structures and fabric covering.
What examiners like: the difference between a thermoset and a thermoplastic, what delamination and disbond mean, tap testing as a basic inspection, and why carbon fibre must be isolated from aluminium. Trap: the "galvanic" link between carbon composites and aluminium turns up in corrosion questions as well as composite ones. Read the composites and non-metallics note.
6.4 Corrosion
The chemistry of corrosion, formation by galvanic action, microbiological contamination and mechanical stress, and the types: surface, pitting, intergranular, exfoliation, stress corrosion cracking, fretting, filiform, crevice and microbiological. B1 and B3 sit the types at level 3, so expect detailed identification questions.
What examiners like: the galvanic series (which metal becomes the anode and corrodes), what each corrosion type looks like and where it is found, why stress corrosion needs both tensile stress and a corrosive environment, and microbial growth in fuel tanks. Drill it with the corrosion topic and the corrosion note.
Exam tip: In galvanic questions, the more anodic (less noble) metal corrodes. Magnesium and zinc are near the anodic end; stainless steel, titanium and carbon are near the cathodic end. If the options include "the more noble metal corrodes", it is the trap.
6.5 Fasteners
Screw threads (nomenclature, forms, dimensions, tolerances, measuring), bolts, studs and screws, nuts, self-tapping screws and dowels, locking devices (tab washers, spring washers, locking plates, split pins, palnuts, wire locking, quick-release fasteners, keys, circlips, cotter pins), and aircraft rivets, solid and blind, with their identification and heat treatment.
What examiners like: thread terms (pitch, major and minor diameter), bolt head markings and grip length, which locking method is self-locking and which is positive, the direction of wire locking (it must pull in the tightening direction), and rivet head and material codes. Trap: a self-locking nut is not to be used where the bolt rotates. Use the fasteners drill and the fasteners note.
6.6 Pipes and unions
Rigid and flexible pipes and their connectors, and the standard unions used for hydraulic, fuel, oil, pneumatic and air systems.
What examiners like: flared versus flareless fittings, identification bands and colour codes on pipes, minimum bend radius for flexible hoses, and why a hose must not be installed twisted (the lay line shows it). Category A sits this at level 2, the same as B1.
6.7 Springs, 6.8 Bearings and 6.9 Transmissions
Spring types, materials and uses; bearing purpose, loads, materials and types (ball, roller, needle, plain, tapered); then gear types and ratios, idler gears, mesh patterns, belts, pulleys, chains and sprockets.
What examiners like: which bearing takes radial load, which takes thrust, and which takes both; brinelling and false brinelling; calculating a gear ratio and the effect of an idler gear (it changes direction, not ratio). Trap: in a two-gear train, the driven gear turns the opposite way; add an idler and it turns the same way. The pipes, springs and bearings note covers 6.6 to 6.8.
6.10 Control cables
Cable types, end fittings, turnbuckles and compensation devices, pulleys and cable system components, Bowden cables and flexible control systems.
What examiners like: why a cable tension regulator is needed (temperature changes the airframe and cable differently), how to check a turnbuckle is in safety, and common cable faults at pulleys and fairleads. Read the transmissions and control cables note.
6.11 Electrical cables and connectors
Cable types and construction, high-tension and coaxial cables, crimping, connector types, pins, plugs, sockets, insulators, ratings, coupling and identification codes.
What examiners like: the parts of a coaxial cable, why crimping is preferred to soldering in aircraft wiring, and connector identification. Installation, testing and inspection practice belongs to Module 7 EWIS, so keep the line between "what it is" (Module 6) and "how you install it" (Module 7). See the electrical cables and connectors note.
Module 6 and Module 7: study them together
The syllabus puts material identification in Module 6 and practical work in Module 7 maintenance practices. Springs, bearings, transmissions, control cables, pipes and rivets appear in both: Module 6 asks what they are, Module 7 asks how to inspect, fit and repair them. Studying the two back to back means you learn each component once, from both angles. Module 6 also feeds the airframe structures parts of Module 11, where the same alloys and corrosion protection appear on a real airframe. For B1 candidates, the Part-66 B1 licence guide shows where the module sits in the full set.
The physics behind stress, strain and elasticity comes from Module 2, so if you have not yet sat it, read its statics section before the testing parts of 6.1 and 6.2.
How to prepare for Module 6
Build tables, not paragraphs
Module 6 is mostly identification and comparison. Make your own tables: alloy series against main element and use; heat treatments against purpose; corrosion types against appearance, cause and typical location; locking devices against positive or friction locking; bearing types against load direction. Tables like these are faster to revise than notes and match how examiners frame the questions.
Weight your time by the size of each sub-module. In our bank, composites and non-metallics, fasteners and electrical cables and connectors have the most questions, followed by the non-ferrous and ferrous metals and corrosion. Springs, pipes, bearings and transmissions are smaller, but they are quick to learn, so do not skip them: on an 80-question paper, a handful of easy questions can be the difference between 58 and 60 correct.
Use your hangar time
If you work in maintenance, look at the hardware you handle with Module 6 in mind: read the part numbers on bolts and rivets, check pipe identification bands, look at how a turnbuckle is locked. Exam questions about identification become memory rather than theory.
Free and Pro practice
- Free Module 6 quick practice: 20 questions with explanations, no account.
- B1.1 Module 6 paper 1: a full timed paper at 80 questions (EASA) or 72 (UK), free. Choose the rules on the start screen.
- Printable Module 6 sheet: 50 questions with answers to print or save as PDF. EASA and the CAA do not publish past papers; these are exam-style questions written for the app.
- Pro on the pricing page adds papers 2 to 10, sub-module drills and all study notes for every category, with no pass guarantee.
Booking and retakes
Sit Module 6 at a Part-147 organisation or with the CAA in the UK; the CAA engineer licensing pages explain the process. After a fail you wait 90 days, or 30 days after tailored Part-147 retraining. EASA allows three attempts in any 12 months; the UK allows three consecutive attempts, then a one-year wait. A pass counts for 10 years towards a licence application.
For free background reading, the FAA Aviation Maintenance Technician Handbooks cover materials, hardware and corrosion in depth. They use US specifications and terminology, so check identification systems against your course notes.
Your study plan
- Take the B1.1 diagnostic or the one for your category to see where Module 6 stands.
- Do the free Module 6 quick practice and note your weak sub-modules.
- Read the free ferrous materials note, then build your corrosion and fasteners tables.
- Sit Module 6 paper 1 timed, on the EASA or UK setting that matches your exam.
- Drill corrosion and fasteners until both score above 85%.
- Book the exam when you reach 85% on three different full papers.
20 free Part-66 Module 6 Materials and hardware practice questions with answers
Try each one, then open the answer. For the timed experience use the free exam-style paper or the printable version.
1. Pulse-echo ultrasonic inspection of a composite has the advantage that it:
- A. needs no couplant
- B. works only on sandwich panels
- C. needs access to one side only
Show answer
C. needs access to one side only
In pulse-echo inspection a single transducer sends a pulse and receives echoes from the back wall and any defect. Only one side needs access, and the echo timing shows the depth of the defect.
2. On a wing, in which direction should the major axis of an elliptical corrosion dish-out run?
- A. Spanwise
- B. Chordwise
- C. Diagonally at 45°
Show answer
A. Spanwise
Dish-outs are elliptical with the major axis spanwise on wings and horizontal stabilisers, longitudinally on fuselages, and vertically on vertical stabilisers.
3. In AN bolt numbering, the length code '12' means:
- A. 12/16 in (0.75 in)
- B. 1 2/8 in (1.25 in)
- C. 12/8 in (1.5 in)
Show answer
B. 1 2/8 in (1.25 in)
The length code's first digit is whole inches and the last digit is eighths of an inch. '12' is therefore 1 and 2/8 in, which is 1 1/4 in.
4. How is moisture kept from entering the rear of an environment-resistant connector?
- A. Fill the rear with general-purpose grease
- B. Match wire outside diameter to the grommet sealing range
- C. Wrap the backshell with adhesive tape
Show answer
B. Match wire outside diameter to the grommet sealing range
Moisture entry through the rear is prevented by matching the wire outside diameter to the rear grommet's sealing range and terminating only one wire per crimp contact. Unused cavities get sealing plugs.
5. A rack and pinion converts:
- A. linear motion into faster rotary motion only
- B. high torque into high voltage
- C. rotary motion into linear motion
Show answer
C. rotary motion into linear motion
The pinion is a small gear meshing with a toothed bar (rack). Turning the pinion moves the rack in a straight line, as used in some steering and actuator mechanisms.
6. A dark powder is seen leaking from around rivets in a joint that flexes in flight ('smoking rivets'). The likely cause is:
- A. filiform corrosion under the paint
- B. microbial contamination of the joint
- C. fretting corrosion from small relative movement
Show answer
C. fretting corrosion from small relative movement
Fretting corrosion is caused by slight repeated movement between tight surfaces. The wear debris oxidises and forms dark powder that streaks from the joint. Loose rivets must be investigated and replaced.
7. Metal tubing size is specified by:
- A. outside diameter and wall thickness
- B. inside diameter of the bore only
- C. mass per metre of tube length
Show answer
A. outside diameter and wall thickness
Rigid tubing is sized by outside diameter (in 1/16 in steps) and wall thickness. Both must be known to select a replacement, because the same OD is made in different wall thicknesses.
8. The Charpy and Izod tests measure a material's:
- A. static hardness, as depth of indentation
- B. impact toughness, as energy absorbed by a notched specimen
- C. fatigue strength, as cycles to failure
Show answer
B. impact toughness, as energy absorbed by a notched specimen
Charpy and Izod tests break a notched specimen with a swinging pendulum and record the energy absorbed in joules. This measures toughness under sudden loading and shows whether the steel is brittle, for example at low temperature.
9. Cast aluminium bronze is used for bearings and pump parts because it:
- A. is lighter than magnesium and titanium alloys
- B. has strength and ductility and resists corrosion and fatigue
- C. lubricates itself with embedded graphite flakes
Show answer
B. has strength and ductility and resists corrosion and fatigue
Cast aluminium bronze (about 89 % copper, 9 % aluminium) has high strength with ductility and resists corrosion, shock and fatigue, so it is used in bearings and pump parts.
10. A spring that is loaded beyond its elastic limit will:
- A. take a permanent set and not return to its free length
- B. become stiffer and return to a longer free length
- C. always fracture immediately
Show answer
A. take a permanent set and not return to its free length
Past the elastic limit the material yields; the spring keeps a permanent deformation (set) and its preload and rate are no longer as designed.
11. What component is used where a control cable changes direction significantly?
- A. A pulley
- B. A fairlead
- C. A pressure seal
Show answer
A. A pulley
Pulleys guide cables round changes of direction with minimum friction. Fairleads and rub strips guide cables in nearly straight runs, and pressure seals seal cables passing through pressure bulkheads.
12. Aramid (Kevlar-type) fibre composites are characterised by:
- A. high stiffness and good electrical conductivity
- B. high tensile strength but poor compressive strength
- C. high compressive strength and brittleness
Show answer
B. high tensile strength but poor compressive strength
Aramid fibres are yellow, light and very tough in tension, so they resist impact and vibration well. Their compressive strength is poor, they absorb moisture and they are hard to cut and drill.
13. In the four-digit wrought aluminium alloy system, the 2xxx series has which main alloying element?
- A. Copper
- B. Zinc
- C. Magnesium
Show answer
A. Copper
The first digit identifies the main alloying element: 2xxx copper, 3xxx manganese, 4xxx silicon, 5xxx magnesium, 6xxx magnesium and silicon, 7xxx zinc. 2024 is the best-known 2xxx alloy.
14. Aluminium alloy nuts are NOT used on seaplanes with steel bolts because:
- A. they cannot carry any shear loads
- B. of the higher dissimilar-metal corrosion risk
- C. they are heavier than steel nuts
Show answer
B. of the higher dissimilar-metal corrosion risk
Aluminium nuts on cadmium-plated steel bolts are allowed in shear on landplanes but not on seaplanes, where salt water greatly increases dissimilar-metal corrosion.
15. The voltage drop in the main power wires from the generator or battery to the bus should not exceed:
- A. 10 % of the regulated voltage
- B. 2 % of the regulated voltage
- C. 0.2 % of the regulated voltage
Show answer
B. 2 % of the regulated voltage
With the generator carrying rated current, or the battery at the 5-minute rate, the drop in the main power wires to the bus should not exceed 2 % of the regulated voltage. Separate limits apply between the bus and the equipment.
16. In some planetary reduction gears, the bell gear is on the propeller shaft and the pinion cage is held fixed. What is the result?
- A. Propeller turns with the crankshaft, same speed
- B. Propeller turns opposite to the crankshaft, reduced speed
- C. Propeller is locked stationary
Show answer
B. Propeller turns opposite to the crankshaft, reduced speed
With the sun gear driving, the cage stationary and the bell gear mounted on the propeller shaft, the propeller turns at reduced speed but in the opposite direction to the crankshaft.
17. Fatigue corrosion failure occurs in two stages. What happens in the second stage?
- A. The pits fill with oxide and stop growing
- B. Cracks grow by fatigue even if corrosion stops
- C. The part heals once dried and painted
Show answer
B. Cracks grow by fatigue even if corrosion stops
In the first stage corrosion and cyclic stress together cause pitting and cracks. The second stage is essentially fatigue, with the crack propagating from the pits even if the corrosive environment is removed; failure can occur far below the uncorroded fatigue limit.
18. A bulkhead union fitting is used to:
- A. join two hoses without any clamps
- B. reduce the pressure in the line
- C. carry a line through a bulkhead
Show answer
C. carry a line through a bulkhead
Bulkhead fittings have a longer threaded body with a locknut, so they can be secured through a bulkhead while lines connect to each side.
19. Why are austenitic stainless steels such as 18-8 NOT hardened by heat treatment?
- A. They do not form martensite on quenching
- B. They melt below the hardening temperature
- C. They contain too much carbon
Show answer
A. They do not form martensite on quenching
Austenitic stainless steels keep an austenitic structure when cooled, so quenching does not form martensite. They are strengthened by cold working instead.
20. A cylindrical roller bearing compared with a ball bearing of the same size can carry:
- A. a greater thrust load
- B. a greater radial load
- C. more shaft misalignment
Show answer
B. a greater radial load
Rollers make line contact with the races instead of point contact, so a roller bearing carries more radial load. Standard cylindrical roller bearings carry little thrust and need good alignment.
Frequently asked questions
+How many questions are in Part-66 Module 6?
Under EASA rules: 80 questions in 100 minutes for B1 and B3, 60 in 75 minutes for B2 and B2L, and 52 in 65 minutes for category A. Under UK CAA rules B1 drops to 72 questions and B3 to 60; A, B2 and B2L are the same as EASA.
+What is in Module 6 materials and hardware?
Eleven sub-modules: ferrous and non-ferrous metals, composites and non-metallics including wood and fabric, corrosion, fasteners, pipes and unions, springs, bearings, transmissions, control cables, and electrical cables and connectors.
+Is Module 6 hard?
It is long rather than conceptually difficult. For B1 it is one of the longest papers in Modules 1 to 10, and it asks a lot of identification detail: alloy designations, rivet codes, corrosion types and locking methods. People with hangar experience usually find much of it familiar.
+Which Module 6 topics are most examined?
Neither authority publishes topic statistics. In our bank, composites and fasteners have the most questions, and corrosion types are the only level 3 topic in the module for B1 and B3. Expect several questions on composites, galvanic and stress corrosion, thread forms, bolts and locking devices.
+Is Module 6 shorter under UK CAA rules?
For B1 and B3, yes. The UK B1 paper is 72 questions instead of 80, and the UK B3 paper is 60 instead of 80. Category A, B2 and B2L papers are the same size in both systems, and the topics are the same.
+How is Module 6 different from Module 7?
Module 6 is about what parts are made of and how they are identified: materials, fastener types, pipe types, bearings and cables. Module 7 is about working with them: tools, riveting practice, torque, inspection, wiring practices and procedures. They overlap, so studying them back to back saves time.
+How long should I study for Module 6?
There is no official figure. Because the B1 paper is long and detail-heavy, most candidates need longer than for Modules 8, 9 or 10. Book when you score 85% or more on three different full papers at your category's size.
Study offline on your phone too
The Part-66 Prep: EASA & UK CAA app has the same questions plus a module board, essay coach, units drill and an attempt tracker for resit dates.
Keep reading
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