The reason being?

[BadgerGrowler]

When aircraft are parked at the gate/stand during snowy conditions the slats and flaps are lowered?

Is this to aid the de-icing process?, and if so how does it help?

Regards

BG

[learner001]

They are not intentionally lowered (out or down) for that occasion, but :

they have 'not been retracted back' to the 'zero position' (in or up) after landing, to avoid any adhering remaining frozen pieces of ice, formed during the previous flight in icy conditions, damaging the structure on rertraction.

Kind regards, learner... ;)

[Dave Clarke Fife]

Have seen a US registered B757 (not sure what airline it was) at Dublin and on a very clear, cold, crispy, blue morning sitting on stand with its slats extended (couldn't see the flaps) whilst it was being de-iced. Not a fleck of snow to be seen anywhere. The Lingus A320 and A330 next door had no such items extended. Maybe a 757 or this particular airline SOP????

[Callsign Kilo]

Not 100% sure if this was the case, however it seems like a possibility

CSFF (Cold Soaked Fuel Frost) / NEI (Non Environmental Icing).

I would imagine the 757 had just arrived from the US. Spending a long period of time in the cruise ensures that the temperature of the fuel in the main tanks (wings) gets pretty cold. I am basing by answer with knowledge of the 737NG, however I am pretty sure the 757 will also draw fuel from the centre tank before the main tanks. This leaves the fuel in the wings untouched for a reasonably long period of time. As the aircraft is in the cruise the outside skin gets extremely cold, so naturally the fuel in contact with the wings will also get cold. As the aircraft descends into the warmer air, condensation may form on the aircraft's skin. Alternatively moisture may be picked up as it descends through cloud layers etc. Remembering that the fuel in the wings is still cold, the moisture on the aircraft skin, most particularly the wings, can freeze resulting in a layer of ice forming on the upper and lower services. In most cases that I have experienced the ice usually forms on the lower surface as the fuel that would normally have been in contact with the upper surface of the wing has been used. Often deicing isn't required as when you refuel, the warmer fuel temperature in the tanker melts the ice. However the day that you describe sounds particularly cold and I'm guessing it was probably fairly early in the morning (when surface temperatures are still on the low side).

That's my best reason for such deicing activity. Considering the day in question (crisp, clear and dry with no signs of snow, fog etc)

[G SXTY]

Our SOP (Dash 8 Q400) is to leaves flaps extended after landing if the runway or taxiways are covered in slush. That way, if anything has been thrown up into the flap tracks it can easily be spotted on the walk round and de-iced accordingly.

[groundagent]

They are not intentionally lowered (out or down) for that occasion, but :


One carrier I know parked the night stop aircraft and left them with flaps down when there was a frost warning so the de-icing contractor (with prior approval from the carrier) could complete an early de-ice subject to prevailing conditions and hold over time. This negates the need for the engineers or crew to position the flaps as they are already in position.

I believe the flaps should be down for de-icing to ensure total coverage of leading edge and upper surfaces . . . but I may have made that up and stand by to be corrected :p

GA