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Module 12 Helicopter aerodynamics, structures and systems: 50 practice questions

Real EASA paper: Category A 100 Q / 125 min · B1.3 128 Q / 160 min. Three options, 75% to pass. Answer key on the last page. From part66exam.com · independent study aid, not an official exam or a past paper.

1. Emergency breathing systems carried on offshore helicopters provide:
1. A. a short air supply to help escape under water
2. B. oxygen for high-altitude flight
3. C. smoke protection for the pilots only
2. A sudden increase in 1/rev vibration after a bird strike on a main rotor blade most likely indicates:
1. A. a normal increase due to fuel burn
2. B. blade damage affecting track or balance
3. C. a tail rotor gearbox chip light fault
3. A 24 V, 40 Ah battery can theoretically supply 8 A for:
1. A. 5 hours
2. B. 320 hours
3. C. 3 hours
4. Helicopter VNE usually decreases with increasing altitude because:
1. A. retreating blade stall occurs at a lower airspeed
2. B. tail rotor authority increases with altitude
3. C. engine power increases with altitude
5. Some Fenestron-type fan-in-tail units have blades spaced unevenly round the hub. The main reason is to:
1. A. save weight by using fewer blades
2. B. make the fan turn in both directions
3. C. reduce noise by spreading the blade-passing tones
6. Fire extinguisher squib cartridges must be replaced when:
1. A. the bottle pressure is low
2. B. the fire warning test is done
3. C. their life or date limit is reached
7. On helicopters fitted with an auxiliary power unit (APU), the APU can supply:
1. A. main rotor drive in flight
2. B. fuel pressure for engine start only
3. C. bleed air and electrical power on the ground
8. Fretting at a bolted or riveted joint is dangerous in helicopter structure because it:
1. A. increases the clamping force of fasteners
2. B. damages surfaces and starts fatigue cracks
3. C. seals the joint against moisture
9. Why is an instrument's vibration isolation (shock mount) important in a helicopter panel?
1. A. Vibration improves the accuracy of gyros
2. B. Rotor vibration can damage instruments
3. C. Shock mounts provide the instrument earth
10. Before loading a database, the technician checks:
1. A. the database file size only
2. B. the loader software version only
3. C. the effective date and part number
11. When a fuel quantity gauge reads correctly on the ground but reads low in flight at a nose-down attitude, the probable cause is:
1. A. water contamination in the fuel
2. B. probe coverage changing with attitude
3. C. a blocked fuel tank vent line
12. A permanent hydrophobic coating on a windscreen differs from liquid rain repellent in that it:
1. A. is applied on the ground and lasts for a long period
2. B. is sprayed from the cockpit when it rains
3. C. must be removed before every flight
13. In a typical helicopter IMA layout, the cockpit displays receive their data:
1. A. over the avionics network from hosted applications
2. B. directly from each sensor by separate wires
3. C. from the HUMS ground station
14. The requirement for a main rotor gearbox to continue safe operation for a period after loss of lubricating oil is known as:
1. A. run-dry (loss of lubrication) capability
2. B. freewheel overrun capability
3. C. rotor overspeed capability
15. Integration of HUMS data with the on-board maintenance system allows:
1. A. automatic replacement of worn gears in flight
2. B. vibration findings to be viewed with system faults
3. C. the rotor rpm limit to be increased
16. Phosphate ester hydraulic fluids (e.g. Skydrol) require seals made of:
1. A. neoprene (synthetic rubber)
2. B. butyl rubber or ethylene-propylene
3. C. natural rubber compounds
17. A gear 'unsafe' indication with the selector down and no green light is first checked in the cockpit by:
1. A. retracting the gear again immediately
2. B. pressing lamp test to check the bulbs
3. C. switching off the hydraulic system
18. A tail-mounted white position light on a helicopter shows:
1. A. forward over 110°
2. B. downward only
3. C. rearward over 140°
19. Energy-attenuating helicopter seats are designed to:
1. A. lock rigidly so the occupant cannot move
2. B. fold forward to clear the exits
3. C. stroke downward to absorb vertical crash loads
20. A vertical one-per-revolution vibration is caused mainly by:
1. A. one blade producing more lift than the others
2. B. a spanwise mass imbalance of the main rotor
3. C. a worn hanger bearing on the tail rotor drive
21. On helicopters whose main supply is DC, AC for instruments and avionics is usually provided by:
1. A. transformer-rectifier units
2. B. reverse current relays
3. C. static inverters
22. A single-rotor helicopter with a counter-clockwise main rotor and a vertical mast typically hovers:
1. A. right skid low
2. B. perfectly level
3. C. left skid low
23. In a helicopter control linkage, a bellcrank is used to:
1. A. damp control vibration by friction at its pivot
2. B. limit the maximum travel of the control run
3. C. change the direction of motion and the mechanical advantage
24. After a fire extinguisher bottle has been discharged, the maintenance action includes:
1. A. resetting the fire handle and nothing else
2. B. refilling the bottle with water on the aircraft
3. C. replacing the bottle and checking lines and indicators
25. A bleed air shut-off valve in the heating system is closed when:
1. A. the engine is at maximum continuous power
2. B. a duct overheat or leak is detected
3. C. the helicopter is established in cruise flight
26. Strain in a structural member is:
1. A. the change in length divided by the original length
2. B. the force divided by the cross-sectional area
3. C. the maximum load before failure
27. A radio altimeter measures height by:
1. A. timing signals reflected from the ground
2. B. measuring static pressure
3. C. comparing GPS altitude with the map
28. Helicopter information systems may include:
1. A. the primary flight control computers
2. B. the engine FADEC and its sensors
3. C. electronic logbooks and maintenance data
29. Regulations for newer helicopters require a low-fuel warning to operate when about how much usable fuel remains?
1. A. About 60 minutes
2. B. About 1 minute
3. C. About 10 minutes
30. Small-radius items such as OAT probes, antennas and tail rotor blades collect ice faster than large surfaces because they:
1. A. have a higher collection efficiency for droplets
2. B. are always warmer than the fuselage skin
3. C. are shielded from droplets by the rotor downwash
31. Cooling of IMA cabinets is important because:
1. A. it improves the processing speed
2. B. it reduces electrical noise
3. C. electronics fail or degrade when overheated
32. An impending-bypass indicator on a main gearbox oil filter shows that:
1. A. the oil pressure is too high
2. B. the filter is clogging and will soon bypass
3. C. the oil temperature sensor has failed
33. A no-fault-found (NFF) result on a removed avionics unit often indicates:
1. A. the real cause (e.g. wiring) was not isolated
2. B. that the unit was definitely faulty
3. C. that the software was loaded correctly
34. A high flash point is desirable in a hydraulic fluid because it indicates:
1. A. good resistance to combustion
2. B. low viscosity at low temperature
3. C. good compatibility with all seals
35. On a helicopter with wheeled landing gear, an oleo-pneumatic shock strut absorbs landing energy by:
1. A. compressing a heavy steel coil spring only
2. B. forcing fluid through an orifice and compressing gas
3. C. bending a flexible composite spring leg
36. A downward-facing hover or belly light on some helicopters is mainly used to:
1. A. replace the anti-collision light in cloud
2. B. warn air traffic control of an emergency
3. C. light the area below the helicopter during hover work
37. A cargo hook for underslung loads normally has:
1. A. electrical release plus a manual emergency release
2. B. only a manual release operated on the ground
3. C. no means of release while in flight
38. Medium-frequency vibration (for example 4/rev or 6/rev) becoming stronger than normal is usually caused by:
1. A. a loose airframe part or reduced fuselage damping
2. B. one main rotor blade being out of track
3. C. a worn engine accessory gearbox bearing
39. On a turbine helicopter, DC power is commonly produced by a:
1. A. starter-generator on the engine accessory gearbox
2. B. belt-driven alternator on the tail rotor shaft
3. C. ram air turbine deployed from the fuselage
40. The tip Mach number of a rotor blade is highest:
1. A. on the retreating blade in the hover
2. B. when the helicopter is in autorotation
3. C. on the advancing blade at high forward speed
41. Cyclic feathering alone changes:
1. A. the total rotor lift but not the disc attitude
2. B. the attitude of the rotor disc but not the total lift
3. C. both rotor rpm and blade coning angle
42. A smoke detector of the photoelectric (light refraction) type gives a warning when:
1. A. the temperature rises above a set value
2. B. smoke scatters light onto a photocell
3. C. ionised air current increases
43. An electronic temperature controller for cabin heating on a turbine helicopter typically positions:
1. A. the engine fuel control unit
2. B. a bleed air mixing or modulating valve
3. C. the engine compressor inlet guide vanes
44. The stress that produces twisting of a shaft such as a main rotor mast is:
1. A. compression
2. B. torsion
3. C. hoop stress
45. The ILS localiser gives lateral guidance by comparing two signals modulated at:
1. A. 30 Hz and 9,960 Hz
2. B. 400 Hz and 1,300 Hz
3. C. 90 Hz and 150 Hz
46. Information systems are usually segregated from flight controls to:
1. A. protect critical functions
2. B. reduce the electrical load
3. C. simplify wiring
47. A fuel quantity system that reads high when water is present in the tank is most likely the:
1. A. float type
2. B. sight-gauge type
3. C. capacitance type
48. When a helicopter is de-iced on the ground, Type I de-icing fluid is:
1. A. a thickened fluid for long holdover time
2. B. a rain repellent for the windscreen
3. C. a heated glycol-water mix used to remove ice
49. A laminated-disc (flexible disc) coupling in a tail rotor drive accommodates misalignment by:
1. A. sliding of splines under oil
2. B. flexing of thin metal disc laminations
3. C. rolling of balls in a constant-velocity joint
50. On-board maintenance systems usually separate fault messages into:
1. A. current faults and fault history from earlier flights
2. B. faults caused by pilots and faults caused by passengers
3. C. hydraulic faults and fuel system faults only

Answer key

1. A — Compressed-air or rebreather units give occupants extra time to escape a capsized helicopter.
2. B — Damage (dent, skin debond, lost tip cap weight) changes a blade's aerodynamic or mass properties, producing out-of-track or out-of-balance 1/rev vibration; the blade must be inspected to limits before further flight.
3. A — Time = capacity / current = 40 Ah / 8 A = 5 h (ignoring the reduction in capacity at high discharge rates and low temperature).
4. A — At higher density altitude the retreating blade must work at higher angle of attack, so stall is reached at a lower forward speed. VNE placards often show this variation.
5. C — Uneven (modulated) blade spacing spreads the acoustic energy over several frequencies instead of one strong tone, reducing the noise perceived.
6. C — Squibs contain explosive material with a limited life; they are replaced by date or hours.
7. C — An APU is a small gas turbine providing compressed air for heating/cooling and engine starting and driving a generator, allowing operation on the ground without main engines.
8. B — Small relative movement under vibration causes fretting wear and corrosion, which acts as a crack initiation site.
9. B — Panels or individual instruments are shock-mounted to reduce transmitted high-frequency vibration, which would otherwise shorten instrument life and cause pointer flutter and gyro precession errors.
10. C — Ensure the correct, current data is loaded. Databases have effective periods; loading the wrong cycle or part number gives incorrect data.
11. B — Gauging accuracy depends on probe positions relative to fuel with changing attitude. Multiple probes and calibration compensate; errors are greatest at extreme attitudes.
12. A — Hydrophobic coatings are durable treatments applied during maintenance. Liquid repellent systems spray fluid in flight as required.
13. A — Display applications receive data across the network from IMA modules and data concentrators instead of hard-wired sensor connections.
14. A — CS-29 requires Category A rotorcraft to show that the rotor drive system can continue to operate for a defined period (typically 30 min) after loss of lubrication, to allow a safe landing.
15. B — Combining HUMS and fault data gives maintenance a fuller picture of the helicopter's condition and simplifies record keeping.
16. B — Seal material must match the fluid. Phosphate esters attack neoprene and many paints and plastics; they are also irritant, so protective equipment is used.
17. B — A failed lamp or sensor can give a false unsafe indication. The crew checks lamps, then uses alternate indications and the emergency extension procedure if necessary.
18. C — The white tail light covers 70° either side of directly aft (140° total), completing all-round position light coverage.
19. C — Crashworthy seats include energy absorbers that let the seat pan stroke down in a severe vertical impact, reducing the spinal load on the occupant.
20. A — A 1/rev vertical bounce comes from a lift (track) difference between blades. Spanwise mass imbalance gives a lateral 1/rev; drive shaft problems give high frequency.
21. C — Static inverters use solid-state switching to convert 28 V DC into AC (e.g. 115 V and 26 V, 400 Hz) for instruments, displays and avionics.
22. C — To oppose drift the disc is tilted to the left; with a vertical mast and the tail rotor acting below the main rotor, the fuselage hangs left skid low. Mounting the tail rotor higher on a pylon reduces this lean.
23. C — A bellcrank pivots and converts motion from one direction to another. Changing arm lengths alters the ratio of movement and force.
24. C — The discharged bottle is removed for servicing, new squibs fitted, discharge indicators replaced, and the zone and lines inspected and cleaned per the manual.
25. B — Shut-off valves isolate the bleed supply when not needed or when overheat/leak detectors operate, protecting surrounding structure and systems from hot air.
26. A — Strain (ε) = ΔL / L. Within the elastic range, stress is proportional to strain (Hooke's law) and the ratio is Young's modulus.
27. A — A downward-looking antenna transmits (typically in the 4.2–4.4 GHz band) and another receives the ground return; the time or frequency difference gives absolute height, usually up to 2,500 ft.
28. C — Information systems store and transfer data such as electronic logs and maintenance documents.
29. C — The handbook quotes 14 CFR 27.1305: a warning when approximately 10 minutes of usable fuel remains. The low-level sensor is independent of the quantity gauge.
30. A — Droplets follow the airflow around large, blunt bodies but strike thin objects directly. Small-radius items therefore accrete ice first and fastest.
31. C — Electronic components degrade or fail at high temperature, so cooling air and fans must work.
32. B — A differential pressure indicator pops out before the bypass valve opens. Maintenance must then find the cause of the contamination and change the filter.
33. A — High NFF rates increase cost; better use of CMC data and fault isolation procedures reduces unnecessary removals.
34. A — Flash point is the temperature at which the fluid gives off enough vapour to flash when a flame is applied. A high value reduces fire risk from leaks onto hot surfaces.
35. B — On compression, hydraulic fluid is forced through a metering orifice (dissipating energy as heat) and the nitrogen (or air) charge compresses, acting as a spring. Rebound is damped too.
36. C — Hover lights illuminate the ground or load under the helicopter, supporting hoist and sling work at night.
37. A — The pilot releases the load electrically from a switch on the cyclic; a mechanical release (cable/lever) is provided in case of electrical failure. The hook is load-tested and has a maximum placarded load.
38. A — Medium frequencies are inherent in most rotors. An increase typically indicates loosened components (for example skids or panels) vibrating at that frequency, or changes in airframe damping or mounts.
39. A — The same machine acts as a motor to start the engine and then as a generator once the engine is running, saving weight.
40. C — The advancing tip speed equals rotational tip speed plus forward speed, so compressibility effects appear there at high speed.
41. B — Cyclic feathering increases pitch on one side of the disc and decreases it by the same amount on the other, so net lift is unchanged while the disc tilts. The thrust is redirected to control attitude and direction.
42. B — A light source and photocell are arranged so that clean air gives little light at the cell; smoke particles refract light onto the cell, producing a current that triggers the alarm.
43. B — The controller compares sensed cabin/duct temperature with the selected value and drives the valve that modulates hot bleed air, with overheat limits to protect the system.
44. B — Torsion is produced by torque. The mast transmits engine torque to the rotor and is therefore designed for torsion, as well as bending and tension from rotor thrust.
45. C — The localiser radiates lobes modulated at 90 Hz and 150 Hz; the difference in depth of modulation shows which side of the centreline the aircraft is on.
46. A — Segregation limits the spread of faults and security threats to critical systems.
47. C — Water has a much higher dielectric constant than fuel, so capacitance probes read high when water covers them — another reason for regular draining.
48. C — Type I fluids (usually orange) are unthickened and applied hot to remove contamination; they give short protection. Types II and IV are thickened for longer holdover times.
49. B — Stacks of thin stainless steel discs bolted alternately to each flange flex to take angular misalignment without lubrication. They are inspected for cracked or buckled laminations and bolt security.
50. A — Current faults show what is failed now; the history shows faults from previous flights, helping to diagnose intermittent problems.

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