Materials and Hardware
Core concepts
Know aircraft ferrous and non-ferrous materials: aluminium alloys (2024, 7075), titanium, magnesium, steels, and composites (fibre types, lay-up, honeycomb). Understand heat treatment, corrosion types (galvanic, stress, exfoliation, fretting) and prevention. Hardware includes rivets (solid, blind, Hi-Lok), bolts (AN, MS, close-tolerance), nuts, washers, screws, locking devices, bearings, springs, pipes and unions, and cables and control fittings. You must recognise identification markings and know where each fastener type is permitted.
Traps to watch
- AN versus MS bolt identification: head markings and dash numbers indicate diameter and length; length is measured differently for hex-head and countersunk bolts.
- Grip length: bolt length must suit the material stack; too short or too long is a defect.
- Dissimilar metals: joining aluminium to steel or cadmium-plated parts invites galvanic corrosion; use isolation.
- Hi-Lok and blind rivets: know which are structural and which are non-structural, and where each may be used.
- Composite damage: impact damage may be internal; barely visible damage can still be significant.
Worked example
A bolt dash number such as AN3-5 indicates a 3/16 in nominal diameter series (AN3 = 3/16 in) with a length code of 5 eighths of an inch. Always confirm against the parts catalogue rather than assuming; the dash number encodes diameter series and length, not the thread pitch.
Rule of thumb
Before answering any hardware question, ask: what material, what load path (shear or tension), and what locking method? These three filters eliminate most wrong options.