Aircraft - Technical Specific (airframe, systems and powerplant)
Airframe, systems and powerplant - what is tested
DGCA CPL Technical Specific questions probe whether you understand how the airframe carries load and how systems fail, not just component names. Expect semi-monocoque structures, landing gear, hydraulics, fuel, pressurisation, ice protection and reciprocating/turbine powerplants.
Core rules
- Semi-monocoque fuselage: stressed skin, stringers and frames share load; the wing spar carries bending, ribs hold aerofoil shape.
- Oleo strut: nitrogen preload plus oil metering; torque links align the wheel; shimmy damper stops oscillation; a down-lock microswitch gives cockpit indication.
- Hydraulic pressure comes from resistance to flow; the accumulator smooths pulses and gives limited emergency supply; the relief valve protects the system.
- Fuel: the boost pump prevents vapour lock, vents prevent cavitation, sump drains remove water; unusable fuel is not available in flight.
- Pressurisation: the outflow valve controls cabin altitude; differential pressure is limited by safety valves.
- Reciprocating engine: magnetos are independent of the battery; carburettor icing can occur at outside air temperatures well above 0 °C; a constant-speed propeller uses governor oil pressure.
- Turbine: compressor, combustor, turbine; monitor N1/N2 and EGT, not just fuel flow.
Worked example
A hydraulic actuator has a 3 in² piston and a 1 in² rod. At 2,000 psi, extension force = 2,000 × 3 = 6,000 lbf. Retraction acts on the annulus = 3 − 1 = 2 in², so force = 2,000 × 2 = 4,000 lbf. The asymmetry explains why some actuators are rigged to extend under load.
Traps
Mixing gauge and absolute pressure; assuming a pump alone sets pressure; leaning to peak EGT without watching CHT; treating accumulator precharge as system pressure; and forgetting that a magneto check tests two independent ignition circuits.