ATPL Aero & Systems common mistakes
ATPL Aero & Systems · Understand the traps and how to avoid them.
Treating the maximum load factor as a single number, so the candidate applies the +2.5 g limit to a flap-extended configuration or to a gust case instead of recalling that the limit drops (typically to +2.0 g) once flaps are down and that gust loads are separate design cases.
The clean-configuration symmetric limit is the figure most often memorised, and candidates carry it across every scenario because the certification categories (utility, aerobatic, commuter) and flap positions are rarely rehearsed side by side.
What to do instead
Build a small comparison table before the exam: category, clean limit load factor, flap-extended limit load factor, and the corresponding ultimate factors (limit x 1.5). Practise classifying a described manoeuvre as manoeuvre load, gust load or ground load before quoting a number.
Answering hydraulic questions by quoting pump delivery pressure alone, ignoring that actuator speed depends on flow rate and that system pressure is set by the pressure-relief or pressure-regulator valve, not by pump displacement.
Pump type, pressure and flow are learned as a list, so candidates conflate a variable-displacement pump's ability to hold constant pressure at varying flow with a fixed-displacement pump plus relief valve arrangement.
What to do instead
For every hydraulic question, state three things explicitly: what sets pressure (relief/regulator/unloader), what sets flow (pump displacement and engine or electric motor speed), and what the consumer needs. Rehearse the variable-displacement pump's pressure-compensator behaviour as a closed loop: pressure rises, compensator destrokes, flow falls to match demand.
Mixing up the roles of the outflow valve, the safety relief valves and the negative-pressure relief valve, then attributing cabin altitude control to the wrong component or claiming the outflow valve protects the structure against overpressure.
All three are valves in the same pressure hull and are taught together, so candidates remember 'valves control pressure' without separating normal scheduling (outflow valve), structural overpressure protection (relief valves) and protection against external pressure exceeding internal (negative relief).
What to do instead
Anchor each valve to the failure it prevents: outflow valve modulates flow to hold the selected cabin altitude and rate; safety relief valves open only if the outflow valve fails closed and differential pressure approaches the structural limit; negative relief admits air if the differential reverses. Draw the hull with arrows for each case.
Assuming a generator failure automatically sheds electrical load or that paralleled generators share load equally regardless of their control, instead of identifying which bus is lost, what remains powered and whether the bus tie or essential bus reconfiguration occurs.
Candidates memorise generator ratings and bus names but not the distribution topology, so they cannot trace power from source to a specific consumer through a failure.
What to do instead
Trace a single consumer end to end for three cases: normal, one generator lost, and complete AC loss with battery or emergency generator supply. Learn which buses are essential or battery-direct and which loads are shed automatically. Practise stating the source, the bus and the switching device for each answer.
Describing fly-by-wire protection as if the aircraft simply refuses to exceed a limit, rather than explaining that the computers command a limiting attitude or load factor by prioritising pilot input within an envelope and that protections can be degraded by law reversion.
Marketing-style descriptions of envelope protection are absorbed more readily than the control-law hierarchy, so candidates cannot say what happens when a sensor fails or which law gives what protection.
What to do instead
Learn the law hierarchy for the type in the syllabus (normal, alternate, direct or equivalent) and what each law retains. For each protection (bank, pitch attitude, high-speed, high-AoA, load factor), state the input it acts on and the cue that it is active. Then state the degradation path when redundancy is lost.
Confusing the functions of the anti-skid system and the autobrake system, or claiming anti-skid increases braking pressure, when anti-skid only releases pressure to prevent wheel lock and autobrake only schedules a deceleration level.
Both act on the brakes through the same hydraulic path and both are described as 'braking control', so the direction of their intervention (pressure release versus pressure application) is easily swapped.
What to do instead
Fix the direction of each intervention: anti-skid detects wheel deceleration or slip and dumps pressure at that wheel to restore rotation; autobrake applies and modulates pressure to achieve a selected deceleration. Learn the cues (wheel speed signal, slip ratio) and what happens if each fails: locked wheel versus no automatic braking.
Treating fuel quantity indications as exact and neglecting that unusable fuel, tank shape, attitude and float or capacitance gauging errors mean indicated quantity differs from usable quantity, and that fuel transfer or crossfeed changes the balance calculation.
Candidates compute endurance from indicated fuel without applying unusable fuel and without checking that the tank supplying the engine is the tank being read.
What to do instead
For any fuel question, write the chain: indicated quantity, minus unusable fuel, gives usable fuel; usable fuel divided by consumption gives endurance; compare with the fuel actually in the tank feeding the engine. Note how crossfeed or transfer affects lateral balance and which gauge is valid in the current configuration.
Assuming that any ice-protection system prevents ice from forming everywhere, instead of distinguishing anti-icing (prevents formation) from de-icing (removes accumulated ice) and knowing which surfaces are protected and which are not.
Systems are grouped under 'ice protection' in study notes, so the protected-area boundaries and the timing of operation (continuous versus cycling) are lost.
What to do instead
Classify each system as anti-ice or de-ice and list its protected area: wing leading edge, tailplane, engine intake, propeller, windscreen, pitot and static. Learn the cycling logic of a de-ice boot or thermal system and the consequence of operating it too early or too late. State explicitly which surfaces remain unprotected.
Confusing fire detection with fire extinguishing and mis-stating the detection principle, for example describing a continuous-loop detector as a rate-of-rise detector or claiming a single-loop system still works after the loop is severed.
Detection and extinguishing are taught as one chapter, and the different sensing principles (rate of rise, fixed temperature, continuous loop, optical smoke) blur together.
What to do instead
For each zone, state the detection principle, the number of loops and the failure logic: a single continuous loop that breaks gives a fault; a dual-loop system may still alarm on one loop but needs both to confirm. Separately list the extinguishing agent, number of bottles and discharge sequence for each protected zone.
Describing turbine thrust as rising indefinitely with RPM or confusing shaft horsepower with thrust, and ignoring that thrust falls with altitude and temperature while specific fuel consumption behaves differently from piston-engine figures.
Piston-engine relationships are learned first and then applied to turbines, so candidates expect power to scale with RPM and do not separate net thrust from gross thrust or EPR from N1 as the thrust parameter.
What to do instead
Write the thrust chain for a turbofan: gross thrust from nozzle momentum, minus ram drag, equals net thrust; thrust falls with density and is limited by turbine temperature. Learn which parameter the type uses as the thrust setting (EPR or N1) and how flat-rated thrust holds a constant value up to a break temperature before decreasing.