EASA Module 14 common mistakes
EASA Module 14 · Understand the traps and how to avoid them.
Treating 'compressor stall' and 'compressor surge' as interchangeable in multiple-choice items, so the candidate picks whichever term appears first rather than the one matching the described condition.
Both describe flow breakdown, and study material often uses them loosely. The exam distinguishes a local, recoverable stall of one stage or blade row from a full annulus flow reversal (surge) with loud bang and RPM fluctuation. Candidates memorise one definition and apply it to both.
What to do instead
Build a two-column comparison card: local vs full-annulus, recoverable vs requiring throttle reduction, blade tip vs entire compressor. For each practice item, underline the symptom words (bang, rumble, fluctuating RPM, flame out) before looking at the options, and justify rejection of each wrong option in one sentence.
Calculating turbine blade or disc stress and creep life using the wrong temperature basis, e.g. mixing Celsius and Kelvin, or applying ambient temperature where turbine entry temperature is intended.
Numerical items on turbine materials test whether the candidate knows that creep rate depends on absolute temperature and that TET (not ambient) drives blade cooling design. Candidates rush the unit conversion or grab the first temperature quoted in the stem.
What to do instead
Adopt a fixed routine: convert every temperature to Kelvin first, label which station the temperature refers to (T1, T3, TET), then substitute. Practise 10 items converting between °C, K and °F until the conversion is automatic, and always sanity-check that a turbine entry figure exceeds compressor delivery temperature.
Confusing the firing order and valve events of a four-stroke piston engine with the cylinder numbering, leading to wrong answers on valve overlap, ignition sequence and power-stroke spacing items.
Candidates memorise a firing order as a string without linking it to crank angle intervals. Items that ask which cylinder is on which stroke at a given crank angle then defeat them, because they cannot reconstruct the sequence from first principles.
What to do instead
For a representative inline-four and a radial nine-cylinder engine, draw the full 720° cycle on paper: mark TDC firing for each cylinder at its correct interval (180° for the four, 80° for the nine), then mark inlet opening, exhaust closing and overlap. Redo the diagram from memory weekly until the sequence can be derived, not recalled.
Mixing up the purpose and adjustment direction of mixture, carburettor heat and idle settings, so the candidate answers 'weaken' where 'enrich' is correct, or vice versa, on piston engine fuel system items.
The verbs are similar and the systems interact: carburettor heat enriches the mixture by reducing air density while also preventing icing; leaning enriches or weakens depending on the direction of the control. Candidates learn phrases rather than the underlying air/fuel mass balance.
What to do instead
Write one sentence per control describing the physical change (what happens to air mass, fuel mass, and density), then derive the mixture effect rather than memorising it. Test yourself by predicting the exhaust gas temperature trend for each action; EGT rises toward peak as mixture approaches stoichiometric and falls when richer or leaner.
Describing a lubrication or fuel system component's function by its name rather than by its role in the circuit, e.g. calling a fuel control unit a 'pump' or a scavenge pump a 'pressure pump', and then selecting the wrong component for a fault symptom.
Engine system items are written as symptom-to-component questions. Candidates who know component names but not their position and direction of flow cannot trace a symptom such as low oil pressure at high power or fuel flow rising with altitude compensation.
What to do instead
Draw a block diagram of each system from tank to nozzle or sump to bearing, with arrows and pressure/temperature at each station. Annotate what each component does to pressure and flow. Answer symptom questions only after locating the symptom on your own diagram.
Assuming a propeller blade angle change affects thrust and RPM in the same direction at constant power, and therefore choosing the wrong outcome for an increase in blade angle.
The relationship is indirect: increasing blade angle increases load on the engine, so at fixed power the RPM falls while thrust may rise or fall depending on airspeed. Candidates apply a simple 'more angle equals more thrust' rule that fails at the extremes.
What to do instead
Work through the constant-speed propeller governor loop explicitly: RPM error, pilot valve movement, oil to or from the hub, blade angle change, load change, RPM restoration. Practise predicting RPM, manifold pressure and thrust trends for take-off, climb and descent at fixed throttle, and state the airspeed assumption each time.
Ignoring the direction of rotation and the resulting asymmetric blade effect (P-factor) when answering propeller thrust and yaw questions, treating both propellers of a twin as producing identical thrust at high angle of attack.
Textbook diagrams show a descending and ascending blade but candidates often memorise 'critical engine is the left one' without knowing why, so any variation in the question (counter-rotating, pusher, different rotation direction) breaks the answer.
What to do instead
Derive the effect from blade angle of attack: at high nose-up attitude the descending blade meets air at a higher angle of attack and produces more thrust, so the yaw depends on which side the descending blade is on. Redraw the disc with rotation arrows and the relative airflow tilted, then state the yaw direction for each configuration.
Answering FADEC and engine control items as if the electronic unit directly moves the fuel metering valve, rather than recognising the hydromechanical backup and the distinction between supervisory and full-authority control.
The architecture is layered and the terminology (EEC, ECU, FADEC, hydromechanical unit) overlaps. Candidates learn that 'FADEC controls the engine' and miss items about reversion modes, thrust lever resolution and which functions remain in the hydromechanical unit.
What to do instead
Map the control chain for one engine type: thrust lever angle to electronic unit to torque motor or stepper to fuel metering valve to fuel flow, and mark which elements are electronic and which are hydraulic. Then list what happens in each reversion or degraded mode. Answer only from that map.
Confusing foreign object damage with domestic object damage and misattributing a symptom such as a sudden vibration with debris, when the described evidence (e.g. material matching an upstream component) points to internal release.
Both produce similar compressor damage, and the exam tests whether the candidate reads the evidence in the stem rather than pattern-matching the word 'damage'. Candidates answer from the headline rather than the described material or location.
What to do instead
For each damage item, extract three facts before choosing: what material or component is implicated, where in the gas path the damage sits, and whether the event was sudden or progressive. Use those three facts to discriminate. Build a short table of FOD, DOD, erosion and tip rub with their distinguishing evidence.
Treating engine instrument indications as independent, so the candidate picks an answer that fits one gauge while contradicting another (e.g. high EGT with normal or falling fuel flow and normal RPM).
Troubleshooting items are designed so that only one option is consistent with all quoted indications. Candidates fixate on the most visually striking parameter and ignore cross-checks that would eliminate the option.
What to do instead
Before answering, tabulate every parameter given in the stem and mark each as high, normal or low. Eliminate any option that requires a parameter to move in a direction the stem contradicts. Practise with three-parameter items until the cross-check becomes a reflex.