Chapter 4 - Aircraft Icing Protection Systems

Question 1

What areas of the aircraft are sensitive to ice formation?

Answer 1

Aerofoil surfaces
Engine intakes
Engine internal surfaces
Rotor blades and propellers
Windscreens
Control hinges and linkages
Instrumentation probes and vanes
Weapons and weapon carriers

Question 2

What effects can icing have on aircraft performance?

Answer 2

Thrust decreases (engine not performing as efficiently)

Lift decreases (change in shape of the wing)

Drag increases (ice build up disrupts the airflow across the wing, body and tail)

Weight increases

Question 3

What are the two categories of Ice Protection systems?

Answer 3

Active

Passive

Question 4

How do active ice protection systems work?

Answer 4

Either:

Increase the temp of local areas to above freezing point
or
Chemically reduce the freezing point of precipitation impinging upon the aircraft

Question 5

How do passive ice protection systems work?

Answer 5

Harness the momentum of the main airstream to separate out precipitation and divert it away.

Question 6

What are the categories of Active ice protection systems?

Answer 6

Anti-icing

De-icing

Question 7

What methods are used to alert crews to the risk of ice forming on an aircraft?

Answer 7

Met forecasts

External visible checks

Ice accretion probes - Positioned to be visible from the cockpit

Flood lights

Alerts and automatic systems

Question 8

Why don’t aircraft always fly with ice protection systems turned on?

Answer 8

The systems require a considerable amount of power.

Question 9

What are the different types of Ice Detection Devices?

Answer 9

Visual ice detector

Differential static pressure ice detector

Frequency monitor ice detector

Question 10

Explain how a Visual ice detector works?

Answer 10

Illuminated ice accretion probe viewable from cockpit.

Visual detector - painted matte black to give best visual background to detect ice formation

System can be de-iced in order to observe the rate of ice build up.

Question 11

Explain how a Differential static pressure ice detector works?

Answer 11

Detector monitors pressure differential between a series of holes on the leading and trailing edges of the diff static detector.

Cockpit alert activated when holes on the leading edge become blocked.

Question 12

Explain how a Frequency monitor ice detector works?

Answer 12

Utilises changes in resonant frequency of a probe which occurs when ice forms on it.

Probe vibrated at its clean resonant frequency, any mass of ice will reduce the resonant frequency and the detector senses and significant changes, activates an alarm in the cockpit.

Question 13

What is used for the majority of airframe structure anti-icing and de-icing systems?

Answer 13

Hot air bled from the engines

Must be cooled first and pressure must be reduced.

Question 14

How does hot air enter the wings?

Answer 14

Piccolo Tube

Note - Learn diagram in manual (web, plenum, etc)

Question 15

What components of the engine is Thermal (hot air) anti-icing used to protect?

Answer 15

The inlet guide vanes

First stage compressor stator blades

Nose cone

Nose cowling

Structural support members within the intake

Question 16

Where is electrical heating most useful for anti-icing?

Answer 16

When complex control arrangements are needed or small areas need to be heated.

Normally used for turbo-prop blades.

Question 17

What is used to de-ice helicopter blades and FW props?

Answer 17

Heating mats (thermal - electrical)

Question 18

Explain how pneumatic de-icing boots work.

Answer 18

Layers of rubber with one or more air chambers between the layers.

Placed on the leading edge of an aircraft’s wings and stabilisers.

Chambers rapidly inflated and deflated, rapid change in shape breaks the adhesive force between the ice and the rubber, allowing the ice to be carried away by the relative wind flowing past the aircraft.

Caution - Ice must be carried away cleanly from the trailing sections, or it could re-freeze behind the protected area.

Question 19

How are windscreens protected from icing?

Answer 19

They are heated - thin film on gold used for the heating element and is deposited directly onto the glass.

Both de-ice and de-mist the windscreens.

Question 20

How are windscreens protected from rain during low speed flight.

Answer 20

High-speed windscreen wipers

Question 21

What is Holdover Time (HOT)?

Answer 21

The period of time for which de-icing fluids are effective. Timer starts the moment the first drop is applied.

Aircraft needs to get airborne in this time. If it does not it needs to taxi back and the de-icing process must be repeated.

Note - De-icing pastes/gels applied by the groundcrew melt any present ice + prevents reformation for the duration of the HOT.

Question 22

Where is hot air taken from for de-icing/anti-icing?

Answer 22

From the compressor in the engine

Question 23

What is the relationship between engine anti-icing and airframe anti-icing?

Answer 23

Independent of each other?

Question 24

How is an aircraft prepared for flight in icy/snowy conditions?

Answer 24

Ice, snow and slush deposits are first removed by the ground crew.

After physically removing the majority of deposits, chemical fluid de-icing is used to complete the task?

Question 25

Apart from heated windscreens, how else can we protect the windscreens from ice?

Answer 25

Hot air to de-ice and de-mist?

Wipers?

Note - Check this is correct