Airframe, Structure and Flight Control Actuation
Structure and load paths
Candidates must be able to describe the primary structure and how loads travel through it. The fuselage is a semi-monocoque shell: skin carries shear and hoop stress, stringers and frames stiffen it against buckling, and a few bulkheads pick up concentrated loads (wing attachment, pressure bulkheads, engine mounts). Wings are built around spars (front and rear), ribs and stringers, with the torsion box taking bending and twisting. The empennage carries horizontal and vertical stabilisers plus their control surfaces, often through adjustable attachment points (variable incidence stabiliser) rather than a trim tab.
Control surfaces and actuation
Know the function of ailerons, elevators, rudder, flaps, slats, spoilers and trim, and the difference between manual (cable/push-pull rod), power-assisted and fully powered (hydraulic or electro-hydrostatic) actuation. Traps: confusing a servo tab (aerodynamic assistance that reduces hinge moment) with an anti-balance tab (which increases hinge moment for feel); assuming a variable-incidence stabiliser is a trim tab; and forgetting that spoilers can assist roll and destroy lift as well as drag. Questions also test flutter prevention: mass balance, stiffness, and freedom from free play.
Rule of thumb and worked example
Rule: if hydraulic pressure is lost, an unpowered surface reverts to manual reversion only if the design permits it - check whether the aircraft has manual reversion or an emergency hydraulic supply. Worked example: a question states that the left hydraulic system fails and asks whether the aircraft remains controllable. The correct reasoning is: identify which services are on the left system, identify cross-feed or PTU availability, then state the resulting degradation (for example, slats slow to extend, one aileron unpowered). Never assume full control is retained; answer in terms of the specific architecture given.