DGCA CPL Tech Specific common mistakes
DGCA CPL Tech Specific · Understand the traps and how to avoid them.
When an examiner asks what happens if one magneto fails in flight, the candidate says 'the engine stops' or 'you lose half the power', instead of reasoning that the engine keeps running on the live magneto with a small power loss, slightly rougher running and higher EGT on the affected cylinders.
Dual magneto ignition is memorised as a redundancy slogan rather than as two independent ignition circuits each firing its own spark plug per cylinder. Candidates never trace what a single live circuit can still do, so they default to a binary 'both or nothing' answer.
What to do instead
Draw the ignition system once from memory: engine-driven magnetos, separate plug harnesses, two plugs per cylinder, switch positions L, R, BOTH, OFF. For each switch position write the live plugs and expected indications. Then practise explaining the in-flight magneto check and why the RPM drop is limited (typically around 125 RPM maximum, with a small difference between L and R) so the numbers are anchored to the mechanism.
The candidate describes the constant-speed propeller as if the blade angle is fixed and only RPM changes, or claims the propeller governor controls manifold pressure. They cannot explain what the governor does when RPM tries to rise above the selected value.
The propeller is studied as a separate chapter from the engine, so the governor, oil pressure, counterweights and blade angle are never linked into one control loop. Candidates learn 'blue lever equals RPM' without the mechanism behind it.
What to do instead
Build a single causal chain: selected RPM sets governor spring tension, governor ports oil to or from the propeller hub, oil pressure versus counterweights and feathering spring move blade angle, blade angle changes load, load sets RPM. Then rehearse three scenarios out loud: RPM below selection, RPM above selection, and loss of governor oil pressure (blades driven to fine pitch, RPM tends to overspeed).
When computing landing or take-off distance, the candidate simply scales the book figure by the ratio of actual weight to maximum weight, or ignores wind and runway slope entirely, producing a distance that is far too optimistic.
Performance charts look like simple proportion problems, and candidates apply the arithmetic they already know instead of reading the chart's structure. The non-linear effect of weight on lift and on acceleration is not intuitive, and slope and wind are treated as optional extras.
What to do instead
Work every performance question through a fixed four-step routine: pressure altitude from elevation and QNH, temperature to get density altitude, then weight, then wind and slope, applying each correction in the order the chart or graph prescribes. Practise reading one graph type repeatedly rather than many graph types once, and always state units and whether the answer is a ground distance or an air distance.
The candidate answers a centre-of-gravity question by checking only that the loaded CG falls inside the envelope, without checking that it stays inside the envelope throughout the flight as fuel burns, and without distinguishing the forward limit case from the aft limit case.
Loading is taught as one arithmetic exercise (moments divided by weight) and the envelope is drawn as a single point to be tested. The consequences of each limit, and the fact that fuel burn moves the CG, are learned as trivia rather than as a reason to re-check.
What to do instead
For every loading question, compute the CG at take-off and again at landing with the fuel actually used, and plot both points. Attach a consequence to each limit: forward limit means reduced elevator authority, higher landing speed and longer take-off run; aft limit means reduced static stability and possible unrecoverable stall or spin characteristics. Answer with both the number and the consequence.
The candidate confuses indicated, calibrated, true and ground speed, and answers a navigation question using TAS where groundspeed is required, or treats indicated airspeed as true airspeed at altitude.
The four speeds are memorised as a list of definitions with no chain connecting them. Position error, instrument error, density error and wind each act at a different stage, and without the chain the candidate cannot tell which correction applies.
What to do instead
Memorise the chain as a sequence with one cause per link: IAS plus instrument and position correction gives CAS; CAS plus density (altitude and temperature) correction gives TAS; TAS plus wind gives groundspeed. Then answer every speed question by naming the link being crossed and the cause of the change before doing any arithmetic.
The candidate describes the pitot-static system as if the airspeed indicator measures dynamic pressure directly, and cannot explain what the altimeter and vertical speed indicator read when the static port is blocked, or what the ASI shows when the pitot tube is blocked.
The instruments are learned as three separate dials with separate descriptions, so the shared pressure source is never used as an explanatory tool. Blockage questions therefore get guessed rather than derived.
What to do instead
Learn one rule and apply it three ways: the ASI compares pitot pressure with static pressure, the altimeter reads static pressure against a set subscale, the VSI reads the rate of change of static pressure. Then derive each blockage case from that rule, for example a blocked static port leaves the ASI behaving like an altimeter, and a blocked pitot with a drain hole lets the ASI fall towards zero as altitude increases.
The candidate treats the turn coordinator and the attitude indicator as interchangeable, or claims the attitude indicator shows pitch and bank directly from the magnetic field, and cannot say which instrument is primary for bank in a rate turn.
Gyroscopic instruments are grouped by name rather than by the property each uses (rigidity in space versus precession) and by the axis each senses. Without that grouping the instruments blur together.
What to do instead
Make a two-column table: rigidity in space (attitude indicator, heading indicator) and precession (rate gyros in the turn coordinator and turn needle). For each instrument record the gimbal axis, what it indicates and its inherent limitation, such as the attitude indicator's erection and acceleration errors or the heading indicator's need for periodic alignment with the magnetic compass.
When asked about radio failure or a communication procedure, the candidate recites phraseology but cannot state the correct transponder code, the meaning of the emergency frequency, or the priority order of actions after loss of communication.
RT is studied as vocabulary to be repeated rather than as a procedure with a purpose. Candidates learn the words without the decision sequence that tells them which words to use and when.
What to do instead
Learn the standard codes and frequencies as fixed facts (7700 general emergency, 7600 radio failure, 7500 unlawful interference, 121.5 emergency frequency) and then rehearse the loss-of-communication sequence in order: squawk 7600, continue according to the last clearance or the published procedure, transmit blind on the appropriate frequency, and land as soon as practicable. Say the sequence aloud until the order is automatic.
The candidate answers a navigation question using the magnetic compass heading as the track, forgetting variation and deviation, or mixes up track, heading and drift when solving a wind triangle.
Variation and deviation are memorised as two definitions that sound alike, and the wind triangle is drawn once in a textbook and never redrawn. The candidate has no physical picture of which arrow is which.
What to do instead
Draw the wind triangle every time with labelled arrows: true track and groundspeed along the ground, true heading and TAS through the air, wind vector closing the triangle. Then apply the corrections in a fixed order (true to magnetic by variation, magnetic to compass by deviation) and state which correction you applied. Use the memory aid that variation is between true and magnetic and deviation is between magnetic and compass.
The candidate answers airframe and system questions, such as those on hydraulic or electrical systems, by listing components rather than explaining what happens when a pump, alternator or bus fails, so the answer never states the consequence for the flight.
Systems are revised as diagrams to be labelled, which rewards recall of names but not understanding of flow. Exam questions are usually phrased as failure scenarios, so a component list cannot answer them.
What to do instead
For each system, trace the flow from source to user once (engine-driven pump, reservoir, filter, selector, actuator, return) and then answer three failure questions in writing: what still works, what is lost, and what the pilot must do. Structure every systems answer as source, path, user, failure consequence.