Brunei DCA CPL AGK - Airframe, Systems & Power Plant common mistakes
Brunei DCA CPL AGK - Airframe, Systems & Power Plant · Understand the traps and how to avoid them.
When asked what happens to hydraulic pressure and actuator speed as a demand valve opens, the candidate answers from a single pump curve and ignores that system pressure is held by the accumulator and pressure regulator until pump flow is exhausted.
Candidates memorise component lists (reservoir, pump, accumulator, valve, actuator) as isolated facts and never build a mental model of flow versus pressure, so they cannot predict transient behaviour during high demand.
What to do instead
For each hydraulic system, draw a flow path from reservoir through pump, filter, pressure regulator, accumulator and selector valve to actuator and back. Practise explaining what the accumulator supplies in the first seconds of heavy demand and what the pressure regulator does once flow demand exceeds pump delivery.
Treats all DC generation as identical, so the candidate cannot say which bus is powered by the battery, which by the generator, and what happens to non-essential loads when a generator drops offline.
Study is done from a schematic picture rather than by tracing power flow, and the candidate never distinguishes generation, distribution and protection as three separate functions.
What to do instead
Build a one-page bus map from memory: battery to essential bus, generator to main bus through contactor and reverse-current protection, and load shedding order. Then answer practice questions by tracing the map aloud before choosing an option.
On landing gear questions the candidate confuses the functions of the downlock, the squat switch and the anti-skid control unit, attributing anti-skid action to the wrong component or assuming anti-skid works at very low taxi speed.
These are all 'gear-related boxes' learned together without linking each to its physical purpose, and anti-skid is studied as a brake system rather than as a wheel-speed-sensing control loop.
What to do instead
Write one sentence per component stating the condition it senses and the action it commands. For anti-skid, state explicitly that it modulates brake pressure by comparing wheel speed to aircraft reference speed and is inhibited below a low-speed threshold.
Answers fuel management questions by assuming all tanks feed all engines all the time, or that fuel quantity indication alone is sufficient to confirm a transfer valve has operated.
The candidate memorises tank locations and pump types but not the feed logic, crossfeed philosophy or the difference between quantity indication and flow indication.
What to do instead
Learn the feed schedule as a sequence: which tanks feed which engine in normal, crossfeed and transfer modes, and which indications (quantity change, flow, low-pressure warning) confirm each action. Rehearse a fuel imbalance scenario step by step.
In ice and rain protection the candidate says bleed air anti-ice and electrical anti-ice are interchangeable, or forgets that some surfaces use thermal anti-ice while others use pneumatic de-icing boots, and mixes up the two mechanisms.
The systems are grouped under one topic heading and learned as a list of heated surfaces, without separating anti-ice (prevent formation) from de-ice (remove formed ice) and without linking each to its energy source.
What to do instead
Make a table with columns: surface, method, energy source, control and indication. Classify each entry as anti-ice or de-ice. Then explain why a failed timer on a cycling system matters and what indication the crew would see.
On fire detection the candidate claims any detector loop break causes an immediate warning, or cannot distinguish a fire warning from an overheat or a fault indication, and on oxygen cannot state when the passenger system is chemically generated versus stored gas.
Warning logic is learned as a single 'light comes on' idea, and oxygen is studied only as a mask and regulator without the generation and distribution architecture.
What to do instead
For each system, write the detection logic as cause and effect: what a short does, what an open circuit does, how a fault is annunciated differently from a fire, and what test function proves the loop. For oxygen, state source type, storage or generation, regulation stage and the indication that quantity is low.
On piston engine questions the candidate mixes up the induction, compression, ignition and power sequence when asked about valve timing or ignition timing, and cannot explain why a magneto has two independent circuits or what a dropping rpm on magneto check indicates.
The four-stroke cycle is recited as a chant without linking each stroke to the component that performs it, and magneto checks are memorised as a procedure rather than understood as a test of two separate ignition paths.
What to do instead
Draw the cycle with valve positions and ignition event marked on each stroke. Then explain the magneto check in terms of which circuit is being isolated, why rpm falls on one magneto, and what an excessive drop or rough running indicates about timing or the spark plug circuit.
On constant-speed propeller questions the candidate says the propeller governor changes blade angle directly in response to airspeed, rather than explaining that the governor senses engine rpm and controls oil pressure to the pitch-change mechanism to hold the selected rpm.
The governor is visualised as a simple linkage to the throttle, and the distinction between the speed-sensing pilot valve and the pitch-changing force (oil pressure versus spring and counterweights) is never separated.
What to do instead
Describe the loop: selected rpm set by the pilot lever, governor compares actual rpm, pilot valve ports oil, oil pressure or spring force moves blades, rpm returns to selected value. Then state what happens on oil pressure loss for a single-acting versus double-acting system, including feathering.
On gas turbine questions the candidate confuses compressor stall with surge, or cannot say why a bleed valve opens during start and low-power operation, and mixes up the lubrication system's role in sealing and cooling with its role in reducing friction only.
Compressor and turbine sections are learned as a list of stages with no attention to the axial velocity and pressure relationships that create stall and surge, and starting is memorised as a checklist without the reason for each action.
What to do instead
Explain stall and surge in terms of angle of attack on the compressor blades and axial velocity: local breakdown versus full annulus reversal. Link bleed valves, variable stator vanes and start sequence to keeping the compressor off its surge line. For lubrication, list cooling, cleaning, sealing and corrosion protection alongside friction reduction.
On airframe structure and flight controls the candidate treats primary and secondary controls as a naming exercise and cannot explain what makes a control primary, or how a balance tab or anti-balance tab reduces or increases stick force.
Controls are memorised as a list (aileron, elevator, rudder, flaps, trim) without the criterion of affecting the aircraft about a primary axis in normal flight, and tabs are learned by name only.
What to do instead
State the criterion for primary control (direct control of pitch, roll or yaw) and classify each surface against it. For tabs, describe the force path: tab deflection creates a hinge moment that moves the surface, and explain anti-balance versus balance tab effect on control force.