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De-icing (of my plane only) at SEA on Sunday when it was 44 degrees

De-icing (of my plane only) at SEA on Sunday when it was 44 degrees

Old Dec 23, 19, 7:26 am
  #1  
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De-icing (of my plane only) at SEA on Sunday when it was 44 degrees

Delta 2124 yesterday (Dec. 22), scheduled 10:08 AM departure from SEA-SLC. Plane was about 15 minutes late pushing back seemingly on account of holiday Kettles who don't understand the concept of "quickly store your stuff and step out of the aisle", while some families were bringing enough stuff on board to open a pre-school.

Then we push back 20 feet and the captain comes on the PA and tells us they need to de-ice the wings, which they do at the gate. That process added another 15 minutes to the delay. I and my seatmates were a little perturbed because we all had tight connections in SLC (40 minutes in my case). According to the National Weather Service (I just checked), it was well above freezing at the time: 44F. And it had been 44F during the entire hour or so that the plane was parked at the gate. No precipitation was recorded in the previous 12 hours. Visibility was 10 miles and skies were a broken overcast. And, for you weather nerds, the dewpoint was 40F. I did not see any de-icing happening to any other plane at SEA. I had a window seat over the left wing and I saw no ice or frost whatsoever.

Obviously anyone knows that you never want to attempt to take off with ice on the wing. But Is it possible that there was a cockpit crew here engaging in some sort of stealthy "labor action"? Or trying to make some sort of a point? I will be happy to accept that this was a legitimate need for deicing if it can be explained to me why it could be the case that this one plane (but not 99 others) needed to be deiced when it was more than 10 degrees above freezing.

BTW, I made my connection in SLC but only after what seemed to be a 3/4 mile sprint that got me to the departure gate sweaty and out of breath just seconds before they closed the door.
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Old Dec 23, 19, 8:08 am
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2 possibilities:

Ice accretion on inbound flight. Not enough time/temp to melt it off during the turn. Could be CAVU and 44F but still need a Type1 spritz.

Or super-cooled fuel in wings + temp/dewpoint spread which would allow for dew formation that would freeze due to wing temp.
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Old Dec 23, 19, 8:46 am
  #3  
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There is not only the possibility that the Captain and First Officer were conspiring to delay the flight as part of a labor action, but it is also possible that alien beings took over their minds as part of a vast plot to eradicate life on Earth as we know it.

Occam's Razor suggests that there is a more likely explanation as set forth by H.I.McDonough in #2 .

I vote with Mr. Occam on this one.
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Old Dec 23, 19, 8:48 am
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We deiced at LAS last week when the temp was well into the 40s. Better safe than sorry.
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Old Dec 23, 19, 8:52 am
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Yeah, I prefer to rely on the decisions of the flight crew and not a Monday Morning Pilot.
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Old Dec 23, 19, 8:54 am
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Originally Posted by Mr. Tickets View Post
Yeah, I prefer to rely on the decisions of the flight crew and not a Monday Morning Pilot.
Technically, it was Sunday morning
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Old Dec 23, 19, 8:59 am
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Maybe they were training or checking the equipment. Seems like a minor inconvenience
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Old Dec 23, 19, 9:23 am
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Wow. Crazy
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Old Dec 23, 19, 9:33 am
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Ive had this happen at JAC in fall and spring. Often there are multiple flights leaving at 7:00 am, when the tower opens. Usually all A319s from Delta, United and American. Sometimes one flight crew will elect to de-ice while the others will just go. If a captain wants to be de-iced, he or she is the final authority.
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Old Dec 23, 19, 9:37 am
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And you of course had access to the control panels and had done a thorough walk around of the aircraft to validate your visual analysis of the left wing (top only?) from your window seat?

As others stated, Ill trust the folks getting paid to make the decision.
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Old Dec 23, 19, 9:58 am
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The fuel in the wing tanks gets very cold during flight and cools the wing upper, and lower, surfaces in the areas of those fuel tanks. Warmer air, on the surface, can hold more moisture than the colder air at altitude. That warmer, moist air comes in contact with the cold wing surfaces and results in either condensation or, if the wing is cold enough, frost.

A thin layer of frost on the underside of the wing is not a problem but when the frost forms on top of the wing it must be removed, or allowed to melt, prior to takeoff.

I had to have our wings spray last night in Anchorage for exactly the same reason.
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Old Dec 23, 19, 11:14 am
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Also could have been a temperature inversion, coupled with the fuel cooling the wing surface. Always better safe than sorry, and hard to speculate without knowing the full picture.
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Old Dec 23, 19, 12:01 pm
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Respectfully, does the OP hold an ATP and type rating on the 737? This was not a stealthy labor action, just a prudent decision by the crew.

In the past, I've actually had passengers criticize my decisions on things like dropping the gear out of sequence and such, because they "thought" they knew better than me, while sitting in the back. No disrespect to the original poster, just sharing that passengers usually don't have the full picture as to why we may do something they think is unusual or superfluous.
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Old Dec 23, 19, 12:08 pm
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Originally Posted by H.I. McDunnough View Post
2 possibilities:

Ice accretion on inbound flight. Not enough time/temp to melt it off during the turn. Could be CAVU and 44F but still need a Type1 spritz.

Or super-cooled fuel in wings + temp/dewpoint spread which would allow for dew formation that would freeze due to wing temp.
The latter is probably accurate here. I was on a SEA flight last week that de-iced under similar circumstances. I was seated over the wing. I noticed that over the fuel tanks (near the fuselage), the wings did not have the shiny surface that the rest of the wings did and you could see outlines of internal components of the wings. Obviously frost, but very difficult to see except in the right light. We underwent the exact same procedure on my flight. And if the pilots did not deice, I absolutely would have called it to the flight crew's attention.
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Old Dec 23, 19, 12:39 pm
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Originally Posted by H.I. McDunnough View Post
2 possibilities:

Ice accretion on inbound flight. Not enough time/temp to melt it off during the turn. Could be CAVU and 44F but still need a Type1 spritz.

Or super-cooled fuel in wings + temp/dewpoint spread which would allow for dew formation that would freeze due to wing temp.
I'd go with option two here. The aircraft had come in from RDU that morning, so any fuel in the wing tanks was going to be quite cold after five and a half hours inflight. Imagine the wing being like a beer glass kept in a freezer, and when removed from the freezer and brought into warmer, more humid air, frost forms on the outside of the glass. If the fuel is cold enough and the air is humid enough, an hour on the ground won't be enough to warm everything up enough to melt any ice that has formed on the wings. There are some interesting videos out there that explain the decision making process of when de-icing is necessary, even in above-freezing and clear conditions.
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