Dear friends and followers, welcome back to my channel. Today's video is an important topic, especially when it comes to cold weather operation.
Why do airplanes have to be de-iced?
So let's get started!
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Now, I'm sure many of you have experienced this before: You get onto your flight home (during Christmas time, maybe),
you get pushed back, you taxi near the active runway, and then the captain announces...
[Captain: Uh, ladies, gentlemen and children, very good morning, ### we're on de-icing treatment ###]
Sounds familiar? A minimum of fifteen minutes delay, guaranteed.
So you might ask, why is it so important to remove the snow and ice from airplanes?
The critical surfaces on an airplane, such as the wings and control surfaces (like the slats and flaps and ailerons,
and horizontal and vertical stabilizers) have to be free of any contamination.
Because even minor levels of contamination will have a negative impact on aerodynamic performance,
frost, ice or snow accumulation with a roughness of equivalent to medium sandpaper can reduce the lift by much as
30% and increase drag as much as 40%.
Therefore, the changes in lift and drag significantly increase the stall speed and lower the angle of attack,
reduce controllability, and result in a major impact on the airplane's flight characteristics.
To make matters worse, most airplanes have stall speed warnings, which come active at a preset speed or angle of attack,
meaning in case of ice on the wings, the crew might not even receive a stall warning at all. So any kind of
contamination of the critical surface needs to be thoroughly looked at during the outside check, and there are
many different types of icing which can be found on the airplanes. For example,
overnight frost, very similar to what you remove off of your car for the freezing night; clear ice
which can be difficult to detect as it is transparent
and it is a result of frozen water patches or snow which is melted and froze up again;
rime ice is mostly experienced during climb and approach phases;
mixed ice, seen when planes are parked outside for long periods where various ice forms freeze,
and then slightly melt and up again.
So how would you deal with ice that has accumulated on your wings before the flight? Now the outside check is
absolutely mandatory, as
contamination could have damaged sensitive instruments like the pitot tubes, the static port, and angle-of-attack instruments.
You might even have to ask for mobile stairs to get a close look of the upper wing
surface. So once you've completed your outside check and have notified the pilot flying about the contaminated wings
et cetera, you want to contact your ground operator to sign you up for airplane de-icing.
You'll then be put on a waiting list and start up your engines
accordingly. Now during taxi, it is standard procedure to extend your flaps and perform a flight control check.
But all standard procedures and checklists shall be on hold until the de-icing of the airplane is completed.
So no flight control inputs or flap extensions shall be made, as the contamination of snow and ice could
potentially damage the flight controls.
Imagine your windscreen
wipers frozen to the windshield of your car, and as soon as you flip the switch, the chance of breaking your wipers is pretty high.
So prior to reaching the de-icing pad, you perform the de-icing
anti-icing procedure on ground checklist. Now as you see here, the checklist
demands engine bleed 1 & 2 off, such as the APU bleed off.
Why is that so? Now the engine bleed system, generated by the engine compressor stage,
partly provides bleed air for the air conditioning system, so in case some of the de-icing fluid (which is primarily a propylene
glycol based fluid, which is fairly toxic) could get sucked into the engine intake and end up in the passenger cabin.
Therefore, you turn off the engine and APU bleed air to reduce the chance of that happening.
Also the ditching push-button comes to on, which has the function that all exterior inlet and outlet
valves get closed, in case the plane ditches in water (so to say, sealing the aircraft). Now for instance, the big
outflow valve at the rear part of the fuselage
closes, because you don't want de-icing fluid running into the airplane. Once the checklist is completed, the airplane is ready for spraying
operation. You then notify the de-icing crew via radio communication
which areas of the plane you want to get de-iced, and then they get started. [Radio communication: Okay,
681, brakes are set; we are ready. 681, good morning.
We copy that. It's gonna be wings and tail, Type I. We begin de-icing right now.]
The fluid sprayed unto the wing is also known as a
freezing point depressant. These fluids are most effective when the fluid is thermally heated and sprayed onto the wing with a high pressure.
Now, these fluids can come in various mixtures and are categorized in fluid types
which have different effect once they are applied to the airplane.
Type I is primarily used as a
de-icing agent to remove ice, frost, or snow from the aircraft surfaces, and is applied hot, and it's usually dyed orange.
Type II is often applied in a two-step process. The first application is a
heated de-icing fluid to remove most of the
contamination, and the second step is the same fluid but non-heated,
and it acts as an anti-icing agent. Then there's Type III fluid which is a compromise out of the Type I and II,
which is generally applied to turboprop aircraft, as they have a lower lift of speed than jet-propelled airplanes.
And I'm sure many of you have seen Type IV fluids, as they have this green jelly look-alike texture.
Type IV is very often used in collaboration with either Type I and II fluids
which remove the contamination, and then a green layer of anti-icing Type IV fluid is applied to
significantly increase the hold over time. Type II, III, and IV
fluids all have anti-icing properties such that, when applied to a clean surface,
they are designed to protect the aircraft from ice accumulation for a
predicted length of time (the so-called holdover time). The ground crew will inform you about the type and mixture
they have used and when the spraying operation has started. You then open up the holdover time table to check how long the
application will "hold over" until your takeoff.
Let's quickly take a look at the holdover time table. The METAR indicates light snow showers.
The reported temperature is -4 degrees.
Reading down from the conditions and across from temperature, you derive a holdover time for undiluted
Type IV fluid of 30 to 55 minutes. So once the spraying operation is
completed, you perform the "Upon completion of spraying operation"
checklist. You then make sure that all the ground equipment is removed with confirmation of the ground crew, and then resume the normal
operation and perform the checklist leading up to the takeoff roll, such as flight control checks and flap settings.
Please take my advice -- do not underestimate even minor ice patches on your airplane's critical surfaces. Very
often it's difficult to determine if there is ice or not, especially in low-light conditions.
Also, keep in mind airplanes are built out of alloy and composite materials
which react differently to ice. So sometimes one surface seems clean, but the other might be contaminated.
So be wise and get rid of your ice. Please be aware
this is just a basic explanation of the de-icing and anti-icing operation.
There is so much more to learn, trust me. So next week
we'll talk about how airplanes deal with ice within flight. Thank you very much for your time.
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so you won't miss out on upcoming videos. All the best. See you next week, your Captain Joe.
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