NCAA AME Airframe cheat sheet

Primary structure (wings, fuselage frames, spars, pressure bulkheads) carries flight, ground and pressurization loads; failure is catastrophic, so all repairs require approved data and certified personnel sign-off.

Secondary structure (fairings, cowlings, stringers, floor panels) carries only aerodynamic or minor local loads; damage tolerance limits are looser but still defined by the Structural Repair Manual (SRM).

Limit load is the maximum expected in service; ultimate load is 1.5 × limit load, and structure must withstand ultimate load for 3 seconds without failure (yield allowed).

Safe-life and fail-safe/damage-tolerance are the two design philosophies; damage-tolerant designs use inspectable crack-stopping features (stringers, tear straps) and mandated inspection intervals.

Zinc-rich primers protect aluminium skins by sacrificial action; alclad sheet has a pure aluminium cladding; never mix carbon-fibre composite and aluminium without isolation to prevent galvanic corrosion.

Riveted joint types: lap joints in shear, butt joints with splice plates; rivet pitch typically 4–6D, edge distance at least 2D, and hole clearance matched to rivet diameter class.

Control surface rigging checks: correct cable tension (tensiometer per rigging chart), no binding, correct travel and balance; mass balance weights must be restored after painting or repair.

Hydraulic systems: reservoirs pressurized to prevent pump cavitation, relief valves set below component proof pressure, and system identification by colour-coded fluid and placards.

Corrosion types to recognise: surface/general, galvanic, pitting, intergranular, exfoliation and stress corrosion cracking; exfoliation appears as lifting flakes and requires structural assessment, not just blending.

Corrosion-prone zones: battery compartments, bilge areas, wheel wells, lavatory and galley floors, exhaust-trail areas and faying surfaces under fasteners - inspect per CPCP intervals.

Corrosion Corrosion Prevention and Control Programme (CPCP) baseline tasks must be completed within the specified interval; findings beyond allowable limits escalate to a full structural evaluation.

Composite damage classification: allowable damage limits (ADL) may be blended out; damage beyond limits requires SRM-approved bonded or bolted repair by qualified personnel.

Lightning strike protection on composite structure uses a conductive mesh; after a strike, inspect for delamination by tap test or NDT before return to service.

Fuel system safety: bonding and grounding resistance checks before refuelling, no ignition sources in the zone, and tank entry only under confined-space procedures with purged atmosphere.

Maintenance records must capture work performed, approved data used, parts and serial numbers, and certifying signature; airworthiness directives are mandatory and must be recorded as accomplished.

Weight and balance: empty weight and CG must be re-established after major repair or modification, and the aircraft returned within the certified CG envelope for all loading cases.