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De-Icing in the dry

Posted: Sun Nov 03, 2019 10:25 am
by pdp
Last night I was at LUZ/EPLB with the girlfriend and a friend and we were watching a Ryanair 738 to Dublin preparing to depart (it's not an area with a lot of things to do of a Satuirday evening).

Now, first of all, the METAR was something along the lines of 21010KT 06/06 Q1002. Whilst the static air temperature was reasonable for the time of night (2200 local) the wind was absolutely bitter and made it feel a good 5-10c colder than it was. There was no precipitation of any sorts and the taxi from stand to runway is about 50 metres (albeit a 1.3knm backtrack is required).

What surprised me was that despite the rather mild (for Poland in November at least) conditions, they then pushed the aircraft onto the de-icing pad and proceded to spray it. Being far away we couldn't see what fluid type it was.

My Q is, why would you de-ice when there wasn't any snow or rain in the area? I would have expected the aircraft's anti-ice system to be sufficient.

Re: De-Icing in the dry

Posted: Sun Nov 03, 2019 11:38 am
by jumpship
The fuel in the wings gets cold soaked while flying and when the plane is on the ground moisture can freeze to the upper surface of the wings.

Re: De-Icing in the dry

Posted: Sun Nov 03, 2019 12:43 pm
by Starlionblue
As jumpship says, the wings are cold. I've been dripped on from melting ice during walkarounds in 30 degree weather.

Re: De-Icing in the dry

Posted: Sun Nov 03, 2019 1:28 pm
by pdp
Thanks both!

Re: De-Icing in the dry

Posted: Mon Nov 04, 2019 3:48 pm
by Tristarsteve
And the aircraft antice system does not usually work on the ground. On most jet airliners it is inhibited by weight on wheels, to stop the wing getting too hot.

Re: De-Icing in the dry

Posted: Wed Nov 06, 2019 2:13 pm
by 26point2
Tristarsteve wrote:
And the aircraft antice system does not usually work on the ground. On most jet airliners it is inhibited by weight on wheels, to stop the wing getting too hot.


Not true. Anti ice systems can work on the ground, it is required to, for take off in icing conditions. Also, aircraft anti ice systems don’t heat the top or bottom of wings, only the leading edge of wings. Any ice on top or bottom is unaffected by aircraft anti ice.....thus de-ice fluid is used.

Re: De-Icing in the dry

Posted: Wed Nov 06, 2019 4:08 pm
by Tristarsteve
Well the wing antice system on the A320 does not work on the ground. There is a test switch which opens the wing antice valves, they stay open for a few seconds, and then the overheat sensors close them again. If you select wing antice on, these valves will open at lift off.
The A330 is similar, but the valves open for 30secs on the ground, and then close, to open again in the air.

Re: De-Icing in the dry

Posted: Wed Nov 06, 2019 4:28 pm
by GalaxyFlyer
Depends on the plane—all BBD products allow use of anti-ice systems on the ground.

Re: De-Icing in the dry

Posted: Wed Nov 06, 2019 5:37 pm
by Francoflier
pdp wrote:
What surprised me was that despite the rather mild (for Poland in November at least) conditions, they then pushed the aircraft onto the de-icing pad and proceded to spray it. Being far away we couldn't see what fluid type it was.


Did they only do one pass or two?

In clear weather, only the hot de-icing spraying might be done to clear the wings of any contamination accumulated on the ground.
If there are precipitations or icing conditions, or if some might be expected before takeoff, then the second coat of cold anti-ici fluid would be applied as well.

In your case, if the temperature and dewpoint were the same, then icing conditions might have been threatening, even if they were not present when they dispatched.

Re: De-Icing in the dry

Posted: Wed Nov 06, 2019 9:16 pm
by Starlionblue
GalaxyFlyer wrote:
Depends on the plane—all BBD products allow use of anti-ice systems on the ground.


To expand, on the A330, wing anti-ice does not work on the ground. However, engine anti-ice does.

Re: De-Icing in the dry

Posted: Wed Nov 06, 2019 10:19 pm
by GalaxyFlyer
To clarify.all the bizjets and the CRJs allow and require the use of wing and cowl anti-ice on the ground in icing conditions. The exception being when Type IV is applied, then wing anti-ice is ON at the start of the take-off run.

Re: De-Icing in the dry

Posted: Wed Nov 06, 2019 11:04 pm
by DiamondFlyer
GalaxyFlyer wrote:
To clarify.all the bizjets and the CRJs allow and require the use of wing and cowl anti-ice on the ground in icing conditions. The exception being when Type IV is applied, then wing anti-ice is ON at the start of the take-off run.


For what it's worth, so did the DC-9-10 series...