CPL AGK / Systems common mistakes
CPL AGK / Systems · Understand the traps and how to avoid them.
Treating a hydraulic system as 'pressure equals serviceability' - assuming that because the pressure gauge reads normal the system is fully serviceable, and missing that a depleted accumulator or an isolated sub-system can still leave a circuit unpressurised or unable to supply peak demand.
Candidates learn the nominal system pressure early and use it as a single pass/fail indicator, so they stop reasoning about reservoir level, pump output, accumulator precharge, selector position and non-return valve isolation as separate links in the chain.
What to do instead
For every hydraulic question, trace the full path: reservoir quantity and pressurisation, pump type and drive, accumulator precharge versus system pressure, valve/selector position, actuator and return. Ask what the gauge actually measures and where in the circuit it sits; a pressure reading at one point does not prove flow capability elsewhere. Practise fault scenarios where pressure is normal but an accumulator precharge is low or a check valve has failed.
Confusing anti-icing with de-icing and misassigning the correct protection to each airframe zone, for example assuming thermal bleed air is used on surfaces that are actually protected by pneumatic boots, or expecting a weeping-wing fluid system to protect the whole wing rather than a limited leading-edge area.
The two terms are taught together and sound interchangeable; systems also vary between aircraft types, so candidates recall one installation and apply it universally instead of reasoning from the purpose (prevent ice forming versus remove ice already formed) and the surface concerned.
What to do instead
Anchor each answer to the definition: anti-icing prevents accretion, de-icing removes it after it forms. Then build a small table by zone - wing leading edge, tail leading edge, engine intake, propeller, windscreen, pitot/static - listing the method used and whether it is evaporative, running-wet or cyclic. Learn the control logic (timer cycles, holdover times, ice detector inputs) so you can answer from principle when the type is unfamiliar.
Mixing up the roles of the battery and the generator/alternator in DC generation and distribution, such as assuming the battery carries the normal continuous DC load in flight or that a generator failure automatically means total electrical loss.
Both are DC sources and both appear on the same bus diagram, so candidates conflate 'source of power' with 'source of emergency power' and forget that the battery's main jobs are starting, emergency supply and transient stabilisation, not continuous supply.
What to do instead
Draw the DC distribution from memory: battery, generator/alternator, regulator, contactors, bus bars, essential/emergency bus, and the diodes or split system that decide who feeds what. Note which loads are on the battery-only bus and what sheds on generator loss. Then practise questions by asking 'which source is feeding this bus right now, and what happens if it fails?' rather than memorising a single normal configuration.
Assuming fuel gauging is a direct, trustworthy measure of usable fuel, and ignoring that quantity indications can be affected by attitude, sensor type, tank shape, transfer sequencing and unusable fuel, or forgetting that fuel management includes crossfeed and transfer logic, not just total quantity.
Fuel questions look like simple arithmetic ('how much fuel, how long'), so candidates skip the system architecture and treat the gauge as a dipstick. They then miss items about capacitance probes, float switches, imbalance limits and transfer/refuel valve operation.
What to do instead
Learn the gauging method on the type (capacitance, resistance float, ultrasonic), what it actually measures (mass or volume, compensated or not), and its known errors in turns, climb and low quantity. Separately memorise the management rules: tank selection, crossfeed use and restrictions, transfer sequence and indications, refuel/defuel valve control, and the definition of unusable fuel. Answer fuel questions by first fixing the tank state and valve configuration.
Treating landing gear and braking questions as pure component recall and failing to reason about the sequence and interlocks - gear extension/retraction logic, uplocks and downlocks, squat switches, antiskid operation, and the difference between normal, alternate and emergency extension.
The gear system has many named parts, so candidates memorise names and skip the logic that links them. Antiskid in particular is often answered as 'prevents skids' without understanding wheel-speed sensing and brake-release modulation.
What to do instead
Learn the gear cycle as a sequence with conditions: selector, hydraulic or electric actuation, uplock release, downlock engagement, indication and warning, and what inhibits retraction on the ground. For brakes, separate the hydraulic supply, the metering valve, the antiskid control unit and the wheel speed sensors, and be able to say what happens if each fails. Include the alternate/emergency extension method and the associated speed limitations.
Confusing pitot pressure, static pressure and their combination when explaining instrument indications, and misidentifying which instruments are pitot-static, which are gyroscopic and which are electrically driven - leading to wrong answers on blockage, leak and lag effects.
The three pressure sources feed several instruments, and candidates learn the instrument names before the plumbing, so they cannot predict the indication for a blocked pitot, a blocked static or a leaking line.
What to do instead
Build a matrix of instrument versus pressure source versus failure symptom: pitot blocked gives airspeed behaving like an altimeter, static blocked affects airspeed, altimeter and VSI in different ways, and a static leak changes all three. Separately classify gyroscopic instruments by their power source and erection principle, and note which have emergency or standby supplies. Reason from the pressure being measured, not from the dial.
Assuming pressurisation is simply 'bleed air in, cabin altitude out' and missing the roles of the outflow valve, pressure controller, safety valves and the relationship between cabin altitude, differential pressure and structural limits.
Cabin environment questions are often answered from everyday experience of cabin altitude rather than from the control loop, so candidates cannot explain what regulates outflow, what limits differential pressure, or what happens when the controller or a valve fails.
What to do instead
Learn the loop explicitly: bleed air source and conditioning, cabin inflow, outflow valve position controlled by the pressure controller, and the independent safety and negative-pressure relief valves. Be able to state the two limits being protected - maximum differential pressure and maximum cabin altitude - and which component protects each. Then work failure cases: outflow valve stuck open, stuck closed, controller failure, and loss of bleed air.
Mixing up fire detection and fire extinguishing - describing detector types (loop, thermal, optical) as if they extinguish, or forgetting that protection includes detection, warning, isolation of the affected system and the discharge of extinguishing agent into a defined zone.
Fire questions are grouped as one topic, and candidates memorise 'fire bottle' as the answer to everything, missing the separate questions about detector operation, zone identification, warning indications and the actions that isolate fuel, hydraulic and electrical supplies.
What to do instead
Split the topic in two. Detection: detector type, principle of operation, test facility, warning indication, and false-warning causes. Protection: agent type, bottle and discharge routing, which zones are protected, how many discharges are available, and the isolation actions (fuel shut-off, hydraulic shut-off, electrical isolation) that accompany discharge. Answer by asking whether the question is about sensing the fire or dealing with it.
Treating automatic flight control and avionics architecture as a list of boxes, so candidates cannot say what happens when one unit fails, which systems are duplicated or dissimilar, or how the autopilot interacts with the flight director, servos, trim and the navigation sensors.
The architecture is abstract and rarely seen physically, so candidates memorise names and acronyms and skip signal flow and redundancy. Questions then expose that they do not know which component commands, which actuates and which monitors.
What to do instead
Learn the chain: sensor sources (air data, attitude, navigation), the flight director/autopilot computer, the mode logic, the servo or actuator, and the feedback and trim interaction. For each element, note what happens on its failure and what redundancy or reversion exists. Draw the architecture once from memory and label the interfaces; then answer questions by following the signal rather than recalling a component name.
Applying a remembered figure - a tyre pressure, a differential pressure limit, an oxygen duration, a gear speed or a battery voltage - without checking the conditions it applies to, and treating type-specific values as universal.
Numbers are easy to memorise and feel like safe answers, so candidates recall a value from one aircraft or one condition and apply it to a differently worded question. Systems limits are conditional on configuration, altitude, temperature or certification basis.
What to do instead
When a question involves a limit, first identify what is being limited and under which condition, then decide whether a general principle or a type-specific figure is being asked for. Learn principles and relationships (what a limit protects, which component enforces it) rather than isolated numbers, and keep type figures in a clearly labelled table so they are not confused with general knowledge. If a specific figure is not certain, reason from the protected parameter instead of guessing.