Aircraft General Knowledge – Airframe
Aircraft General Knowledge – Airframe
This domain tests the structure and mechanical systems that carry flight and ground loads: fuselage, wings, empennage, flight controls, landing gear, pressurisation and ice protection. The exam expects you to connect load paths, materials and inspection limits to safe operation, not just name parts.
Core concepts
- Primary controls are ailerons, elevator and rudder; secondary controls are flaps, slats, spoilers, trim and tabs. Each changes lift, drag or pitching moment and affects the others.
- Limit load is the maximum expected in service; ultimate load is 1.5 times limit. The structure must carry ultimate load without failure, but permanent deformation is allowed. Beyond limit load, the aircraft is not considered airworthy until inspected.
- Fail-safe and damage-tolerant design uses multiple load paths, crack stoppers and inspection programmes. Corrosion is controlled by protective finishes, drainage and scheduled checks.
- Pressurisation loads the fuselage as a pressure vessel; a cabin altitude above about 8,000 ft requires oxygen for crew under most rules. Landing gear absorbs landing energy through shock struts and tyres, and shimmy is damped by torque links and steering dampers.
Worked example
An aircraft has a limit load factor of +3.8 g. The ultimate load factor is 1.5 × 3.8 = +5.7 g. If a manoeuvre is estimated to reach 5.0 g, it is above limit but below ultimate: the aircraft may not have failed, but it must be inspected before further flight and the exceedance reported.
Traps
- Confusing limit and ultimate load.
- Assuming a control surface only affects one axis.
- Treating a hard landing as harmless without an inspection.
- Ignoring the effect of flap or gear extension on stall speed and load.