ATPL(A) 021 Airframe, Systems, PowerplantRevision notes and practice questions

021 Airframe, Systems, PowerplantFree sample, 10 questions

1. 1A turbofan has an inlet mass flow of 400 kg/s and an HP compressor mass flow of 80 kg/s. What is its bypass ratio?

   1. 4
   2. 9
   3. 5
   4. 8
   Show the answer

   Answer A. The bypass ratio is the bypass mass flow divided by the core mass flow. All the air entering the HP compressor goes through the core: 80 kg/s. Bypass flow = 400 − 80 = 320 kg/s, so the ratio is 320 / 80 = 4. Dividing the total inlet flow by the core flow (400 / 80 = 5) is the common trap.

2. 2A jet operator's home base is close to the sea coast. The operator has issued a directive to wash the undercarriage and fit engine covers after every flight back to base, although the aircraft maintenance manual (AMM) contains no such procedure. Which statement is correct?

   1. The operator foresees a high risk of all or part of the aircraft corroding over time, and this will reduce the chances of corrosion.
   2. The undercarriage is prone to corrosion, so regular washing will not have much effect.
   3. This should not be done, as it is neither recommended nor described by the manufacturer.
   4. The operator wants to keep the hangar floors clean.
   Show the answer

   Answer A. Salt-laden sea air leaves chloride deposits on the airframe, and the landing gear and engine intakes are among the most exposed areas. Washing the gear after each flight and fitting covers limits the build-up of salt and moisture, so the operator is simply adding preventive measures suited to its environment. The AMM sets a minimum standard: the absence of a procedure in the manual does not forbid an operator from doing more.

3. 3Light aircraft and helicopters may be fitted with a "blowdown" emergency gear extension system for use after a hydraulic failure. Which gases are used, and how do they reach the actuators?

   1. Nitrogen or compressed air, which is routed to parallel actuators on the landing gear.
   2. Carbon dioxide or compressed air, which is routed to parallel actuators on the landing gear.
   3. Nitrogen or compressed air, which is routed through a manually operated shuttle valve.
   4. Helium or carbon dioxide, which is routed through a manually operated shuttle valve.
   Show the answer

   Answer C. A blowdown system stores nitrogen or compressed air in a bottle. When the pilot releases it, the gas passes through a shuttle valve that moves across, isolating the failed normal hydraulic line and sending the emergency pressure into the same gear actuators. No separate parallel actuators are needed, and helium or CO2 are not used for this purpose.

4. 4On which of the following principles do aircraft ice detectors operate?
   1. Vibration
   2. Sound detection
   3. Pressure
   4. Tactile

   1. 1 and 3.
   2. 2 and 4.
   3. 1 and 2.
   4. 3 and 4.
   Show the answer

   Answer A. The common ice detectors use vibration or pressure. The vibrating-probe type senses the drop in resonant frequency caused by the mass of ice on its rod, while the differential-pressure type compares pressures from small holes that become blocked by ice. Neither sound detection nor a tactile principle is used for ice detection.

5. 5Under CS-25 for aeroplanes and CS-29 for helicopters, what does the term unusable fuel mean?

   1. Fuel always remaining in the tank irrespective of the aircraft attitude, due to design limitations.
   2. The quantity of fuel not available for use but still shown on the fuel contents gauge.
   3. Fuel that is drained from the aircraft because of water contamination.
   4. Fuel which can be drained during taxi.
   Show the answer

   Answer A. Unusable fuel is the quantity that cannot be delivered to the engines under the most adverse feeding conditions, because the pump inlets are not at the very lowest point of the tank. It is a fixed amount set by the design and included in the basic empty mass. It is not shown as usable on the gauges, since indicating it would mislead the crew about the fuel actually available.

6. 6Which of the following statements about DC electric motors are correct?
   1. If a motor seizes, the applied EMF is equal to the back EMF
   2. If a motor seizes, the applied EMF is equal to the net EMF
   3. If a motor runs away, the applied EMF is equal to the back EMF
   4. If a motor runs away, the back EMF is equal to the net EMF

   1. 2 and 3.
   2. 1 and 4.
   3. 1 and 3.
   4. 3 and 4.
   Show the answer

   Answer A. The armature sees a net EMF equal to the applied EMF minus the back EMF, and the back EMF is proportional to rotor speed. When the rotor seizes, speed and back EMF fall to zero, so the whole applied EMF becomes net EMF and the current surges (2). In a runaway the speed rises until the back EMF approaches the applied EMF, leaving almost no net EMF (3).

7. 7The engine lubrication system is slowly losing oil. Which indications can be expected as a result?

   1. Low/fluctuating oil pressure, high oil temperature.
   2. High/fluctuating oil pressure, low oil temperature.
   3. Low/fluctuating oil pressure, low oil temperature.
   4. High/fluctuating oil pressure, high oil temperature.
   Show the answer

   Answer A. With less oil in circulation the pump can no longer maintain a steady supply, so the pressure drops and fluctuates as air is drawn in. The smaller quantity of oil also removes less heat from the engine, so the oil temperature rises. The tempting option with low pressure and low temperature gets the temperature trend wrong.

8. 8On a FADEC-controlled gas turbine engine, what happens if a single input data item fails?

   1. The engine is set to a fail-safe thrust.
   2. The engine continues to operate normally.
   3. The engine control unit uses a fixed default value for that data in its computation.
   4. The engine shuts down.
   Show the answer

   Answer B. FADEC inputs are duplicated: each critical parameter is measured by dual sensors and cross-checked between the two channels. If one input fails, the system uses the valid source from the other sensor or channel and the engine keeps running normally, usually with only a maintenance message. Fail-safe or default-value modes are only used when no valid source remains, not after a single failure.

9. 9During the test sequence of the fire detection system, the "TEST" light does not illuminate and the pilot has no other visual confirmation. Assuming the indicator light itself is serviceable, which statement is correct?

   1. The circuit is not grounded because of a break in the wire between the detectors, therefore the light(s) will not illuminate.
   2. This is normal. There is a problem only if the "FAIL" light illuminates during the test sequence.
   3. As long as the aural indication sounds, the system is operating properly, because the aural cue has a higher priority.
   4. This is normal. The light(s) remain(s) off because there is no real fire.
   Show the answer

   Answer A. The test switch simulates a fire and checks the continuity of the detection circuit, so a serviceable system must show its light during the test. If the lamp is known to be good and it stays off, the circuit is not being completed, typically because of a broken wire between detectors. A missing test indication is never normal, and an aural warning alone does not prove the whole loop is intact.

10. 10What are the basic functions of a smoke hood?

    1. To seal a smoke source by covering it tightly, so that the smoke stops through oxygen starvation and the source cools down.
    2. To provide breathable gas and protect the user's eyes, nose, and mouth from toxic fumes and smoke.
    3. To protect the entire body of the user against toxic fumes, smoke, and heat.
    4. To protect the user from flames and smoke irritating the eyes by providing goggles that are integrated in the smoke hood.
    Show the answer

    Answer B. A smoke hood (protective breathing equipment) is pulled over the whole head. It supplies breathable oxygen from its own chemical source and shields the eyes and airways from smoke and toxic gases while a crew member fights a fire. It is not a fire blanket, does not protect the body, and gives no protection against flames.