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Module 13 EASA Part 1 > 13.15 Ice and Rain Protection > Flashcards

13.15 Ice and Rain Protection Flashcards

1
Q

What effect does icing on forward facing areas of an aircraft cause?

A
  • Decrease in lift (loss of streamline flow of air around the leading edges and top surfaces)
  • Increase in drag (rough surface increases skin friction)
  • Decrease propeller efficiency (change in blade shape)
  • Loss of control (restriction of control surfaces)
  • Increase in weight (CofG affected as well)
  • Blockage of pitot static heads
  • Obscured windows and windshields
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2
Q

What is supercooled water?

A

Water is present in liquid form at a temperature below the freezing point of 0°C

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3
Q

What is collection efficiency?

A

Measure of how much ice an aerofoil collects compared with the moisture content of air, droplet size and airspeed

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4
Q

For a small radius leading edge, what can the collection efficiency be?

A

95%

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5
Q

Why might the horizontal stabiliser have a higher collection efficiency than the wing?

A

It has a smaller radius than that of the wing

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6
Q

Where will Glaze icing or Runback icing occur?

A

In very dense clouds

Water particles are large and only slightly supercooled
or
In supercooled rain where the water droplets are of a large size

Temperatures range from 2°C to –10°C

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7
Q

What does glaze or ‘runback’ ice consist of?

A

Transparent or translucent coating of ice with a glossy surface appearance

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8
Q

Why is glaze or ‘runback’ ice considered the most dangerous?

A

Much greater spoiling effect on the airflow over the various surfaces

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9
Q

How will rime ice appear?

A

Light texture having a white crystalline appearance

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10
Q

Describe hoar frost?

A

Occurs on a surface which is below the freezing point of 0°C

Forms in clear air, water vapour being converted directly into ice crystals forming a white feathery coating

Occurs on the surface of wings where integral fuel tanks are fitted

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11
Q

What has research shown about the relative stalling speed of propeller driven aircraft that are affected by icing?

A

30% above the normal stalling speed

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12
Q

What is the difference between anti–icing and de–icing?

A

Anti–icing – prevents the formation of ice

De–icing – removes ice after formation

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13
Q

What are the four methods used for aerofoil ice protection?

A

Thermal
Electrical
Pneumatic
Fluid

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14
Q

How is bleed air delivered to the leading edge of the wing for anti–icing purposes?

A

Perforated air duct called a piccolo, or spray tube

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15
Q

What pressure is the ice protection system air regulated to?

A

18–20 psi

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16
Q

What is the period for which the tail ice protection will be active for, after the crew push the switch marked TAIL?

A

2 – 2.5 minutes

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17
Q

Overheat switches for ducting which are restricted on the ground, are restricted at what temperature and why?

A

90°C

No cooling airflow from aircraft movement, means components are at risk of overheating

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18
Q

What is the purpose of the amber VALVE light in the wing anti–icing system?

A

While the valve is moving between positions (fully open and fully closed)

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19
Q

What indication is there that a wing anti–icing system is turned on?

A

White ON light

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20
Q

What are the three occasions where you would receive an amber VALVE caption for the wing anti–icing system?

A

Normal operation when the valve is motoring between stops

When there is a discrepancy between the valve position and the switch position

During test

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21
Q

What causes the anti–ice valve, of the wing anti–icing system, to close during ground test and where is it located?

A

Ground overheat sensing switch just outboard of each anti–ice valve

Sensing 90°C approximately

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22
Q

What are spray mats also known as?

A

Heater mats

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23
Q

Where are continuously heated breaker strips fitted and why?

A

Between intermittently heated area

Ensures that small areas of ice removed are small enough not to cause a hazard to the aircraft

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24
Q

How is the heater mat constructed to provide insulation between mat and aircraft structure, and to provide better transference of heat to the outside where ice forms?

A

Outer glass fibre layer is thinner than the inner layer

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25
Q

How is a heater mat protected from rain or hail erosion and impact damage from runway debris?

A

Covered by an erosion resistant coating

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26
Q

Why is the heater mat coating electrically conductive?

A

Electrically bonds the outer surface of the mat to the aircraft structure to provide a discharge path for static charges

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27
Q

Which areas of the heater mats are heated continuously?

A

Extreme leading edge of an aerofoil

Breaker strips between intermittently heated areas

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28
Q

How are de–icer boots held tight to the aircraft when the system is switched off, or during the ‘off’ cycle for that particular boot?

A

Vacuum pressure

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29
Q

Why is estane used as an outer ply on pneumatic de–icer boots?

A

Resistance to abrasion and deterioration

Electrically conductive to provide a path to dissipate static electricity

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30
Q

What would be considered repairable damage to de-icer boots?

A

Cuts and tears less than 0.75 in (19 mm) long

Scuff damage to an area of 4.5 in x 9.5 in (114 mm x 241 mm)

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31
Q

What might be the cause of sluggish inflation and deflation?

A

Obstruction in certain pipelines

Sticking solenoid valves

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32
Q

What might the fluid method of anti–icing also be known as?

A

Chemical method

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33
Q

What are the advantages of fluid ice protection systems?

A
  • Does not require a large amount of electrical power
  • Does not use bleed air from the engines
  • Light in weight, excluding fluid
  • Porous stainless steel or titanium leading edge can resist damage by hail, stones and birds
  • Distributor is installed flush with the aerofoil leading edge so there is no aerodynamic penalty on the aircraft when compared with pneumatic boods
  • Natural runback of the de–icing fluid gives ice protection behind the leading edge
  • Only switched on when icing is encountered and doesn’t require the pilot to estimate thickness
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34
Q

How many pumps are used for fluid ice protection systems and how many are used during priming?

A

Both are used for initial priming

After 3 minutes, one stops, the other pump supplies the complete system

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35
Q

What is the purpose of proportioning units in the fluid ice protection system?

A

Installed at appropriate locations to send the correct amount of de–icing fluid to the individual porous distributor panels

36
Q

How is the fluid ice protection system primed if icing is likely to occur during a flight?

A

Maintained fully primed by running the pump for approximately 30 seconds every 90 minutes

37
Q

What must be carried out after a distributor panel has been installed as part of the fluid ice protection system?

A

Check should be make to ensure that a smooth and continuous profile is maintained both chordwise and spanwise

Test flight must be carried out to check the stall characteristics of the aircraft

38
Q

When painting an aircraft which incorporates a fluid ice protection system, what must you do?

A

Mask the distributor panels with non–adhesive material attached to the panels at the edges

39
Q

What are the four types of ice detector?

A

Ice formation spot light

Serrated rotor ice detector head

Vibrating rod ice detector head

Hot rod ice detector head

40
Q

What happens on a serrated rotor ice detector head under no icing conditions?

A

No opposing torque

Switch contacts remain open

41
Q

Which detector measures torque on a rotor as ice builds up?

A

Serrated rotor ice detector head

42
Q

What is the resonant frequency of the vibrating rod ice detector head?

A

Approximately 40 kHz

43
Q

What happens to the vibrating rod as the ice builds up (vibrating rod ice detector head) and what does this cause?

A

Probe frequency decreases

Detector circuit compares this with reference oscillator, at pre–determined frequency change the ice detector is activated

Red ice warning light on the flight deck is illuminated and probe heater removes the ice, the probe returns to detector mode and the red light turns off

44
Q

What is the secondary benefit of heating a windscreen for de–icing?

A

Heating the vinyl interlayer makes the window more resilient

Better able to withstand possible collision with birds

45
Q

How are windscreen heat sensing elements usually fixed to the windscreen?

A

Embedded within the panel

Held against the window by a rat trap tension spring

46
Q

When the windscreen heating is switched on, why does it take 2 to 4 minutes to reach maximum value?

A

Prevent thermal shock to the window which might cause it to fail

47
Q

In windscreen heating, what does the primary sensing element maintain the temperature of the windscreen at?

A

40°C

48
Q

In windscreen heating, what is the name of the secondary sensing element, what temperature does it regulate the windscreen heat to, and how is this indicated?

A

Overheat sensing element

Higher temperature of 55°C

Overheat light on the control panel

49
Q

What is the effect on maintenance due to the fact that the resistance of windscreen heating elements changes with age (usually increases)?

A

Must be connected to a different transformer to supply a different voltage

Resistance of the windscreen is checked against a chart

A replacement windscreen requires the same procedure

50
Q

What checks might be required if a heated windscreen is replaced?

A

Resistance test
Functional check
Compass swing
Pressure test

51
Q

During testing, if the window is selected on and no heat is felt and no lights illuminate, what might be the cause?

A

May be caused by high ambient temperature

52
Q

What are the four methods of rain removal?

A

Windscreen wipers

Blowing it off using engine bleed air

Windshields which have a hydrophobic coating

Chemical rain repellent

53
Q

Why is pneumatic rain removal system better than windscreen wipers?

A

Tendency of the airflow to reduce the wiper blade pressure on the window

Difficulty in achieving fast enough wiper action to clear the water during heavy rain falls

54
Q

When can rain repellent be used and why?

A

In conjunction with windscreen wipers only to one windscreen at a time

As the fluid ‘foams’ on the window for a short time after application unless wiped

55
Q

How much rain repellent is applied to a windscreen when the switch is pressed?

A

5cc

56
Q

What must be done if rain repellent is inadvertently applied to a dry windscreen?

A

Washed off with water otherwise it will dry within a few hours

57
Q

What should be done before operating windscreen wipers on a dry windscreen?

A

Wet windscreen prior to operation

58
Q

Why should rain repellent not be applied to a dry windscreen?

A

It will form a gum

59
Q

How is wiper blade tension checked?

A

With an accurate spring balance

Attached to the end of the wiper arm and held at 90°

Force required usually about 10 lbs

Force can be adjusted with the blade tension bolt

60
Q

What produces the changeover of power supply for a waste water drain mast?

A

Weight on wheels switch

61
Q

What are the power supplies of a waste water drain mast heater?

A

115v AC
28v DC

62
Q

Where might ice form in an engine?

A

Engine intake

Inlet guide vanes

Nose cone

Leading edge of the nose cowl

First stage stator blades

63
Q

In engine thermal ice protection, what illuminates the green HEAT light?

A

Lower low pressure switch at 5 psi

64
Q

In engine thermal ice protection, what illuminates the amber HIGH PRESSURE light?

A

Upper high pressure switch at 40 psi

65
Q

In engine thermal ice protection, when does a relief valve vent to atmosphere and why?

A

If differential pressure exceeds approximately 5 psi

Protect the nose cowl from excessive pressures

66
Q

What might some of the large high by–pass engines use instead of thermal anti–icing for the nose cone?

A

Small cone of soft rubber mounted slightly offset on the front of the nose cone

Vibrates sufficiently to shake loose any ice that forms

67
Q

When can normal engine intake icing be expected where visible moisture is present?

A

At temperatures of +8°C to +10°C

68
Q

At what total air temperature will the engine anti–icing system come into operation when the push switch is in the ON position?

A

Below 5°C

69
Q

What conditions will cause the engine intake anti–icing to stop operating?

A

System switched off

TAT above 7°C

Propeller rpm below 600

Timer control failure

70
Q

What gives mixed ice (glime) its opaque appearance?

A

Air is trapped in the frozen ice

71
Q

Why is rime ice rougher than other forms of icing?

A

Particles of ice will remain separate and air will be trapped between them thus the ice will be of a light texture

72
Q

What are the dangers when dry icing is encountered?

A

Will not adhere to the aircraft’s surface but can accumulate in auxiliary cooling ducts and engine air intakes

73
Q

What is cold soaking?

A

Lower fuel temperatures at take–off result in even lower fuel temperatures after a period of flight

Sub–zero fuel touching the wing upper surface keeps the wing temperature under 0°C

74
Q

Which component cycles power to the intermittently heated areas and also monitors temperature sensor function?

A

Controller

75
Q

Which deicing system uses inflatable rubber boots?

A

Pneumatic de–icing system

76
Q

Why are the pneumatic boots held fully deflated by the vacuum supply?

A

Minimising aerodynamic drag

77
Q

Describe what happens when the ejector flow control valve has its solenoid deenergised?

A

Main poppet is closed and air will not come out of the valve

Air is sent to the ejector which creates the necessary vacuum for the boots

Air is vented to atmosphere

78
Q

Describe what happens when the ejector flow control valve has its solenoid energised?

A

Solenoid poppet releases the pressure in the chamber above the main poppet

Main poppet moves upward and closes the vent poppet

Pressure switch checks the de–icer boot pressure which is connected to the timer unit

79
Q

What happens when ‘heavy’ is selected on the control panel for the pneumatic de–icer boots?

A

Period between inflation cycles changes from 3 to 4 minutes to 1/2 minute

80
Q

What is the principle of operation of the fluid ice protection systems?

A

A fluid with a low freezing point may be used to keep an aerofoil free from ice

81
Q

What type of fluid is used in the fluid ice protection systems?

A

Glycol based fluid

82
Q

How many heating elements are in a windscreen and how many sensing elements?

A

Two sensing element for automatic control

One heating element

83
Q

In a windscreen heating element, what happens when the sensing element reaches its predetermined temperature, eg 40°C?

A

The current through the sensing element balances a wheatstone bridge

Control unit and power control relays are de–energised, switching off the heating supply

84
Q

What two things happen when the primary sensing element of the windscreen heating circuit fails?

A

Temperature is now controlled at a higher temperature, eg 55°C

Overheat light on the control panel is indicated

85
Q

Why are the pilot’s and co–pilot’s windscreen wiper systems run by separate motors?

A

Ensures that clear vision is maintained through one of the windows should one system fail

86
Q

State the probes and sensors that require to be heated?

A

Pitot probes

Total air temperature probes

Angle of attack sensors

Static vent plates

Engine EPR probe

87
Q

How are the various probes and sensors which require heating powered?

A

115v AC

Module 13 EASA Part 1 (20 decks)

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