DGCA CPL Technical General cheat sheet

Semi-monocoque structure carries loads through stressed skin, stringers and frames; skin resists shear and tension, stringers resist bending, frames maintain shape and carry concentrated loads.

Fail-safe design allows load redistribution after a component fails; safe-life design retires a part after a calculated fatigue life; damage-tolerant design uses inspectability to manage cracks.

Primary flight controls are ailerons for roll, elevators for pitch and rudder for yaw; secondary controls include flaps, slats, spoilers, trim tabs and speed brakes.

A wing spar carries bending and shear; ribs maintain aerofoil shape and transfer loads; a torque box formed by spars and skins resists torsion.

Differential aileron travel, with the up aileron deflecting more than the down aileron, reduces adverse yaw; aileron reversal can occur at high speed due to wing torsional flexibility.

Cabin pressurisation is controlled by an outflow valve; the pressure schedule is set by the cabin pressure controller; maximum differential pressure is a structural limit.

Hydraulic systems commonly operate at about 3,000 psi in transport aircraft; a pressurised reservoir, engine-driven pump, accumulator and relief valve are common elements.

Dihedral gives lateral stability by producing a roll moment that opposes sideslip; sweepback delays compressibility effects but reduces lift slope and can cause pitch-up at stall.

Landing gear: the oleo strut absorbs landing loads; torque links maintain wheel alignment; a shimmy damper prevents nosewheel oscillation; retraction uses hydraulic or electric actuators.

Four-stroke cycle: intake, compression, power and exhaust; the crankshaft turns 720° per complete cycle in a four-stroke engine.

Compression ratio equals cylinder volume at bottom dead centre divided by volume at top dead centre; a higher ratio improves thermal efficiency but increases detonation tendency.

Detonation is uncontrolled explosive combustion after spark ignition; pre-ignition is ignition before the spark. Both raise CHT and can damage pistons.

Carburettor icing can occur at ambient temperatures between about -10°C and +25°C with high humidity; carburettor heat raises intake temperature to melt or prevent ice.

A constant-speed propeller uses a governor to vary blade angle and maintain selected RPM; oil pressure or centrifugal counterweights drive blade-angle changes.

Propeller slip is the difference between geometric pitch, the theoretical advance per revolution, and effective pitch, the actual advance; slip ratio equals slip divided by geometric pitch.

Feathering rotates the blades edge-on to the airflow to reduce drag after engine failure; reverse pitch directs thrust forward for braking on the ground.

Turbine engine Brayton cycle: intake, compression, combustion and exhaust; thrust is produced by accelerating a mass of air; bypass ratio is bypass airflow divided by core airflow.

Compressor surge is a violent reversal of flow often caused by too-high power at too-low RPM; compressor stall is localised separation. Both raise EGT and can cause flameout.

The pitot-static airspeed indicator measures dynamic pressure, total pressure minus static pressure; it under-reads at altitude for a given true airspeed because air density is lower.

The altimeter is a barometer set to QNH or QFE; flying from high pressure to low pressure without resetting the subscale causes the altimeter to indicate higher than actual altitude.

The vertical speed indicator measures rate of change of static pressure; it lags briefly after abrupt pitch changes and reads zero in level flight after stabilisation.

A blocked pitot tube with the drain open makes the airspeed indicator behave like an altimeter; a blocked static port causes the ASI to over-read in climb and under-read in descent.

The attitude indicator and heading indicator are gyroscopic; the attitude indicator uses a vertical gyro, while the heading indicator uses a horizontal gyro and needs periodic alignment.

The turn coordinator shows rate of roll and rate of turn; a standard-rate turn is 3° per second, completing 180° in one minute.

Magnetic compass errors include variation, deviation from aircraft magnetic fields, and turning and dip errors; the compass is read in level, steady flight.

EGT and CHT gauges monitor engine health; turbine EGT is a primary limit; a sudden EGT drop may indicate flameout or fuel starvation.

The radio altimeter measures absolute height above terrain using reflected radio waves; it is used for low-level approach and ground proximity warning, not en-route altitude.

Ohm's law: V = I × R; power P = V × I = I²R = V²/R.

Series circuit: resistances add and current is common. Parallel circuit: voltage is common, reciprocal resistances add, and total resistance is less than the smallest branch.

Aircraft DC systems commonly use 28 V; AC systems commonly use 115 V at 400 Hz; the higher frequency reduces transformer and generator size.

A generator or alternator converts mechanical energy to electrical energy; an alternator typically has a rotating field and a rectifier for DC output.

The battery provides emergency power, engine starting and bus voltage stabilisation; lead-acid and nickel-cadmium batteries have different charging requirements, and Ni-Cd can suffer thermal runaway.

Circuit protection uses fuses and circuit breakers; a circuit breaker trips on overcurrent and should not be reset repeatedly without finding the fault.

Bonding connects metal parts to provide a low-resistance path for static and lightning current; shielding grounds cable screens to reduce electromagnetic interference.

A magneto is a self-contained engine-driven ignition source that generates high voltage for spark plugs independently of the aircraft battery.

ARINC 429 is a common avionics digital data bus; it uses differential signalling and 32-bit words with labels identifying the transmitted parameter.

2024 aluminium alloy has high strength and fatigue resistance but lower corrosion resistance; 7075 has higher strength and lower corrosion resistance; 6061 is weldable and corrosion resistant.

Heat treatment of aluminium alloys involves solution treatment, quenching and precipitation ageing to increase strength; annealing softens the alloy.

Alclad aluminium has a thin pure-aluminium cladding for corrosion protection; anodising forms a protective oxide layer on the surface.

Galvanic corrosion occurs when dissimilar metals contact in the presence of an electrolyte; the more noble metal is cathodic and the more active metal corrodes.

Stress corrosion cracking requires tensile stress and a corrosive environment; it can cause sudden failure, and heat treatment and surface protection reduce the risk.

Fatigue cracks initiate at stress concentrations and grow under cyclic loading; inspection intervals are set by damage-tolerance requirements.

Carbon-fibre reinforced polymer is strong and stiff but brittle; moisture and ultraviolet light degrade the resin; impact damage may cause internal delamination.

NDT methods: dye penetrant for surface cracks, magnetic particle for ferromagnetic surface and near-surface defects, eddy current for conductive surface defects, ultrasonic and radiography for internal defects.

Titanium is strong, corrosion resistant and heat resistant; magnesium is light but prone to corrosion; stainless steel contains chromium for corrosion resistance.

AN bolts are aircraft-grade and MS bolts are general-purpose; bolt grip length must match material thickness so threads do not bear load in the shear plane.

Torque equals force multiplied by lever arm; use a calibrated torque wrench; friction affects actual preload, and dry versus lubricated threads change the torque-preload relationship.

Lockwire must be installed so tension tends to tighten the fastener; cotter pins and self-locking nuts are alternative positive locking devices.

Solid rivets are common in aircraft structures; the upset head is formed during installation; rivet pitch and edge distance affect joint strength.

Hi-Lok and Hi-Torque fasteners provide controlled preload; they are installed with special collars and are often used in high-vibration areas.

Maintenance documentation includes logbook entries, work orders, Airworthiness Directives that are mandatory, Service Bulletins that are recommended, and the MEL that allows dispatch with specified defects under conditions.

Control cable tension must be set within rigging limits; too low causes lost motion, while too high causes excessive friction and wear.

Corrosion prevention includes keeping drain paths clear, applying protective coatings, avoiding electrolyte traps and using corrosion-inhibiting compounds.

When using a torque wrench extension, a perpendicular extension does not change the applied torque; an in-line extension increases effective lever arm and requires a corrected torque setting.