De Icing Proc while HYD system is depressurized.

[okipoki]

Hi folks,

De Ice proc in parking bay before push. Is there any difference between having aircraft HYD system being pressurized or not during being sprayed? In other words, having HYD system pressurized would reduce the chance of de ice agent entering the opening between flight controls and wings/tail?

Thank you very much for sharing your wisdom online! Stay safe, guys.

[Goldenrivett]

Hi folks,
In other words, having HYD system pressurized would reduce the chance of de ice agent entering the opening between flight controls and wings/tail.

if falling snow (or whatever freezing state the water was in) entered the opening between the fight controls and the wings/tail then surely it would be better to let the dicing fluid remove the contaminant before it froze solid later?

[LME (GOD)]

It makes no difference. Spray pattern is always leading edge to aft to prevent fluid accumulation in cavities, and cavities are designed to drain. Some aircraft require specific stab trim settings

[okipoki]

Hi Goldenrivett,

I agree. The problem is, de ice agent can freeze up in the air as well. So I was wondering if pressurizing HYD system before being sprayed could have prevented or reduced the chance or amount of de ice agent trapped in the opening. As far as I know, there's no difference. With or without HYD pressure, the size of opening between the flight controls and wings/tail remains the same in my opinion. But I know I don't know everything about my Boeing. Thus I am here to ask for help.

[okipoki]

LME (GOD),

Thank you, I thought so, too.

[TURIN]

It used to be a requirement to position the 737 stab LE up before deicing to allow any fluid to drain from the elevator/stab hinge line void area. That is the only reason I know of hydraulics on before deicing.

[Capt Quentin McHale]

okipoki,

On your Boeing, you will find rubber "P" seals installed on fixed structure of various sizes and lengths which are designed to rub against and provide an almost airtight seal between airfoil and structure irrespective if hyd sys is pressurised or not.

Have a closer look on your next walk around and you will see some of them, especially when systems are unpressurised and flight controls are drooping. Hope this helps.

[okipoki]

Capt Quentin McHale,

Thank you very much for sharing your wisdom, Sir. I will take a closer look next time when I walk around.

[okipoki]

TURIN,

Thank you for the info.

Just got back from LHR. Stay safe.