Module 11C.1–11C.3 — B3 light aeroplanes: aerodynamic devices and airframe structures

Module 11C / B3 at a glance

The B3 licence covers piston-engine non-pressurised aeroplanes of 2 000 kg MTOM and below (66.A.3(e)). Under Reg. (EU) 2023/989 B3 candidates sit the single Module 11 at the B3 levels: 60 questions / 75 minutes (UK retained Module 11C: also 60 questions). The B3 rating is endorsed with limitations — wooden structure, metal tubing covered with fabric, metal structure, composite structure — unless experience in each is shown (66.A.45(g)). So B3 study must cover all four structure types.

Not in the B3 syllabus: pressurisation, air conditioning and air supply (11.4(a)–(d)); door safety devices/cargo loading (11.3.1(c)); cabin and cargo layout (11.7(b)); fixed fire detection/extinguishing (11.8(a)); actuation/fly-by-wire (11.9(b)(c)); special fuel systems; anti-icing and rain repellent; air–ground sensing; 11.18–11.21.

Sub-module	B3 level
11.1 Theory of flight (a)(b)	1
11.2 Airframe structures — general concepts, strength, construction	2
11.3 Fuselage, wings, stabilisers, control surfaces, nacelles	1

11.1 Theory of flight — controls and devices (level 1)

• Roll: ailerons (differential or Frise to reduce adverse yaw); flaperons on some designs.
• Pitch: elevator on a fixed tailplane or an all-moving stabilator with anti-servo tab; canards on a few designs.
• Yaw: rudder; ruddervators on V-tails.
• High-lift: plain, slotted or Fowler flaps; fixed leading-edge slots on STOL types.
• Drag devices: airbrakes/spoilers on motor-gliders and some light aircraft.
• Tabs: trim tab, balance and anti-balance tabs, servo and spring tabs (larger types), ground-adjustable (fixed) tabs — bent to correct a wing-heavy or yawing aircraft.
• Balance: mass balance (prevents flutter) and aerodynamic (horn) balance (reduces forces).
• Other devices: stall strips (root stalls first), vortex generators, wing fences (rare), wing-tip shapes and winglets.

11.2(a) General concepts (level 2)

• Station identification: fuselage stations, water lines, butt lines, wing stations from datum; zones for access panels.
• Electrical bonding: bonding straps across engine shock mounts (the engine would otherwise have no earth return — starter current would flow through control cables), control surfaces and fuel components; low resistance checks.
• Lightning strike protection: metal skins conduct; composite and wooden aircraft need conductive paths (mesh/strips) to protect fuel systems and wiring — many light composite aircraft have lightning restrictions in the AFM.

11.2(b) Airworthiness requirements for structural strength (level 2)

• Primary / secondary / tertiary structure classification.
• Safe-life, fail-safe, damage tolerance — many light aircraft were certified safe-life (fatigue life limits on wing spars of some types); ageing-aircraft inspection programmes and ADs address spar/attach fitting cracking and corrosion.
• Stresses: tension, compression, shear, bending, torsion; fatigue from gusts, landings and engine vibration. (Hoop stress concerns pressurised fuselages — not B3 aircraft.)
• Drains and ventilation: drain holes in fuselage bottom, control surfaces and fabric (grommets/seaplane drains); ventilation to keep wooden structures dry.
• System installation provisions: grommets, clamps, separation of fuel lines and wiring, chafe protection.

11.2(c) Construction methods (level 2)

Method	Points
Stressed-skin (semi-monocoque) metal	Skins, stringers, formers/frames, longerons, bulkheads, doublers; riveted (solid AN/MS rivets, blind rivets), some bonded
Welded steel tube truss	4130 chromium-molybdenum steel tubes, gas or TIG welded clusters; internally corrosion-proofed (linseed oil/Tube-Seal); covered with fabric over formers and stringers
Fabric covering	Polyester (e.g. Ceconite/Polyfiber) or cotton/linen (older); heat-shrunk, rib-stitched or glued; coated with dope or approved coating system (UV-blocking layer); strength tests with a fabric punch tester/pull test — fabric below the minimum strength must be replaced; inspection rings and drain grommets
Wood	Sitka spruce spars and longerons, birch plywood skins/gussets; glued joints (resorcinol, epoxy, older casein — casein deteriorates); varnish protection; inspect for rot, glue failure, compression failures, moisture (moisture meter), cracks at fittings
Composite	Glass/carbon/aramid fibre with epoxy resin; sandwich (foam/honeycomb core) or solid laminate; white or light colours to limit heat (resin temperature limits); inspect for delamination (tap test, coin tap), cracks, UV damage, impact; repair by scarf patches per manufacturer data

• Assembly techniques: riveting, bolting (AN bolts, self-locking nuts), adhesive bonding, welding (steel tube).
• Surface protection: Alclad, anodising, chromate conversion (Alodine), epoxy primers, paint; varnish for wood; UV-protective layers for fabric/composites.
• Surface cleaning: approved cleaners; avoid solvents on acrylic windows and some composites.
• Symmetry: rigging measurements — dihedral, incidence, diagonal measurements after heavy landings or ground loops.

Key fact: The B3 rating's structure limitations (wood, metal tubing with fabric, metal, composite) can be removed only by showing appropriate experience — so know the inspection methods for all four.

11.3 Airframe structures — aeroplanes (level 1)

Fuselage, doors and windows

• Cabin structure: metal monocoque/semi-monocoque, steel tube with fabric, composite shell, or wood.
• Attachments: wing attach fittings, lift struts and jury struts on high-wing aircraft (strut corrosion — internal inspection, ADs), landing gear attachments, engine mount to firewall.
• Seats: seat rails, stops, locking pins; seat-belt and harness attachments.
• Doors: latches, hinges, secondary locks, door seals; emergency jettison on some.
• Windows/windscreens: acrylic — wash with plenty of water, soft cloth, approved cleaners; no solvents (crazing); covers when parked; stop-drilling limits.
• Towing devices (11.3.1(b)): glider/banner tow hooks and release mechanisms — common B3 work; check release under load and placards.

Wings (ATA 57)

Spars (wood, metal or composite), ribs, skin or fabric; fuel tanks (integral, bladder or removable aluminium tanks between spars); attachment of landing gear (low-wing), struts (high-wing), ailerons, flaps.

Stabilisers (ATA 55)

Tailplane and fin: metal/composite/fabric-covered; stabilator pivot bearings; bracing wires on some older designs (tension and fittings).

Flight control surfaces (ATA 55/57)

Construction (metal ribs and skin, fabric-covered, composite); hinges and horns; balance — mass balance weights (e.g. in rudder/elevator horns); re-balance after repair or repaint.

Nacelles / engine mounts (ATA 54)

• Firewall (stainless or galvanised steel; fireproof sealing of penetrations).
• Engine mount: welded steel tube with rubber shock mounts (Lord mounts); check tube cracks near welds, mount bushing deterioration.
• Cowlings: aluminium or composite; fasteners (Camloc/Dzus); cowl flaps on some.

Exam tips

• B3 = piston, non-pressurised, ≤ 2 000 kg MTOM.
• Fabric strength tested with a punch tester; wood checked for rot and glue failure; composites tap-tested.
• Bond straps across engine mounts are essential for the starter return path.
• Lift-strut and seat-rail inspections are classic light-aircraft items.