Avielevate / DGCA CPL papers / Technical General
DGCA CPL Technical General — question bank and syllabus
How the aeroplane works: principles of flight, airframes and systems, powerplants, instruments, and the technical fundamentals every commercial licence assumes you already have.
What is in this paper
Every chapter we cover for Technical General, with how many questions sit behind each one.
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Sample questions, answered and explained
A few real questions from this paper, with the answer marked and the reasoning
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040037 · Piston Engines
A transmitter fitted with a magnetic sensor, feeding an RPM indicator, drives a magnetic tachometer using:
- Aa three-phase voltage whose frequency varies with RPM; the indicator contains a synchronous motor driven by this signal.
- Ba DC voltage that varies with RPM; the indicator is simply a voltmeter scaled in rev/min.
- Can AC voltage that varies with RPM; the indicator rectifies it through a diode bridge and reads it on a voltmeter.
- Dan AC voltage whose frequency varies with RPM; the indicator converts this into square pulses that are then counted.
Why that is the answer
A magnetic-sensor tachometer transmitter generates an AC signal each time a rotating toothed wheel or magnet passes the pickup coil; the frequency of this AC signal is directly proportional to shaft RPM. The indicator side does not measure the AC amplitude (which is unreliable at low speed) but instead converts the AC waveform into square pulses via a Schmitt trigger/shaping circuit, then counts the pulse rate electronically to display RPM. This makes the reading independent of signal amplitude, wiring resistance, and temperature. The other options describe DC voltage generators, three-phase motor-driven synchros, or rectified-voltmeter systems, none of which is how a modern magnetic pickup tachometer actually works — those describe older electromechanical tachometer generator types, not a magnetic pulse sensor.
040042 · Avionics and Automatic Flight
Angle-of-attack sensors mounted on each side of the forward fuselage produce an electrical signal representing: 1- the angular position of a wind vane 2- a differential pressure in a probe, varying with the angle of attack 3- a differential pressure in a probe, varying with speed. Which combination lists only the correct statements?
- A1,3
- B1 2
- C1,2,3
- D2 3
Why that is the answer
Angle of attack (AoA) vane-type transmitters mounted laterally on the forward fuselage are small pivoting wind vanes that physically align themselves with the local relative airflow direction; as the aircraft's angle of attack changes, the vane rotates, and this angular position is converted into an electrical signal, via a synchro or potentiometer, proportional to the AoA, which is statement 1. Some AoA sensing systems, alternatively or additionally, use a probe with differential pressure ports that sense a pressure differential which varies as the angle of attack changes relative to the probe's slots, which is statement 2. Statement 3, however, describes differential pressure varying with speed rather than angle of attack, which is not the operating principle of an AoA transmitter, since that instead describes a pitot-static or airspeed sensing device, not an AoA sensor. Therefore only statements 1 and 2 correctly describe AoA transmitter operation, giving the combination of statements 1 and 2 as the correct answer, while any combination including statement 3 incorrectly conflates AoA sensing with airspeed sensing.
040071 · Turbine Engines and Propellers
In a turbojet's vibration monitoring system, any vibration the engine produces is:
- Adirectly proportional to engine speed
- Bsent straight to the cockpit indicator with no amplification or filtering
- Camplified and filtered before being sent to the cockpit indicator
- Dinversely proportional to engine speed
Why that is the answer
Raw vibration signals picked up by accelerometers on a turbojet contain a wide range of frequencies and amplitudes generated by rotating components, structural resonances and aerodynamic noise. If fed directly to the cockpit gauge, this raw signal would be noisy, difficult to interpret and prone to false indications. Engine vibration monitoring systems therefore process the transducer signal through amplification (to bring the weak sensor output to a usable level) and filtering (to isolate the frequency band associated with genuine rotor imbalance or engine-related vibration, rejecting irrelevant noise) before it reaches the cockpit indicator. Option a and d wrongly assert a simple proportional or inverse relationship with engine speed, which ignores that vibration amplitude depends on many factors besides RPM. Option b is incorrect because unprocessed signals would make the indication meaningless to the crew; amplification and filtering are essential steps in the signal chain.
040085 · Fuel
An electric float gauge offers advantages including: 1- simple construction, 2- the reading's independence from variations in the aircraft's power system when measured with a ratiometer, 3- the reading's independence from variations in the aircraft's power system when measured with a galvanometer, 4- the reading's independence from temperature variations. Which combination lists all the correct statements?
- A1, 2, 3 and 4
- B1, 3 and 4
- C2, 3 and 4
- D1, 2 and 4
Why that is the answer
An electric float-type fuel gauge uses a float-driven variable resistor to send an electrical signal to a remote indicator, and its advantages depend partly on whether the indicating instrument is a ratiometer or a galvanometer. Statement 1 (ease of manufacture) is a genuine practical advantage, as float-and-potentiometer mechanisms are relatively simple and well-established to build. Statement 2 is correct: when a RATIOMETER (which compares the ratio of two currents/voltages rather than an absolute value) is used as the indicator, the reading becomes largely independent of variations in the aircraft's electrical supply voltage, because a ratiometer inherently cancels out common supply fluctuations affecting both its coils equally. Statement 4 is correct: temperature does not significantly affect the mechanical float-and-resistor sensing principle itself (unlike volume-only indications elsewhere, the electric signal chain here, especially when paired with appropriate mass-compensation, is relatively independent of temperature effects on the electrical measurement). Statement 3 is false: a GALVANOMETER (which responds to absolute current magnitude) does NOT provide the same independence from supply voltage variations that a ratiometer does - a galvanometer's reading would drift if supply voltage varies. This is why statements 1, 2, and 4 form the correct combination (option d), while statement 3 (claiming galvanometer indication is also independent of power supply variation) is the false statement that must be excluded.
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