EIPremier From United States of America, joined Sep 2000, 1550 posts, RR: 1 Posted (3 years 2 months 2 weeks 2 days ago) and read 2175 times:
Just observed something at SEA today which struck me as curious, and was wondering if the tech/ops community had any insight. I was waiting at the C concourse around 11 am today (2/17), and I saw two planes being deiced at the gate prior to pushback. One was a 739 going to SJD and the other was a 738 going to GEG. The odd thing was both aircraft had come in from other cities, so they weren't RON aircraft. Furthermore, the outside temp was way above freezing (44 deg F according to wunderground), and the cloud deck was low, but no precip since the prev evening. Not that I'm questioning their decision to de-ice, but I just couldn't really figure out why it was needed. Anyone have any insight?
okie From United States of America, joined Jul 2003, 3784 posts, RR: 3
Reply 1, posted (3 years 2 months 2 weeks 1 day 23 hours ago) and read 2160 times:
Quoting EIPremier (Thread starter): The odd thing was both aircraft had come in from other cities, so they weren't RON aircraft. Furthermore, the outside temp was way above freezing (44 deg F according to wunderground),
There is your clue. They flew in from an altitude that was -44F and had cold soaked the plane, wings in particular.
With thousands of pounds of Aluminum and Fuel cold soaked to -44F then when sitting on the ramp the wing started to form frost.
I can not count the times that I have waited for de-icing on an aircraft but I would say 70% of the time was in conditions that you mentioned 40-45F and humid, night or cloudy.