Cold weather ops

[Jonny Foreigner]

Evening all....

Trying to find out variations/observations (if any) in standards regarding the following.

Having been de-iced/anti-iced does anyone use improved climb/high Vr techniques (assuming a non contaminated runway and it being sufficiently long enough) for take off?

Understanding the shearing properties of the fluid on the wing are one reason not to apply the above method. But having an improved margin over stall might push you the other way? Especially if you are not using wing A/I having just been anti-iced.

Any thoughts appreciated...

[Tugging Pilot]

Can't help you there my friend,

That said I would like to use your post to pose another question...... (sorry)

Do you or anyone out there know exactly why (the exact easy to understand physics) an airframe will lose ice (without the use of boots etc) if the aircraft leaves icing conditions, but the outside air temperature still remains below zero. I know the process is called sublimation and I know how sublimation works in the way SLD turn to ice immediately.....what I don't know is how sublimation works in the opposite direction with OAT below zero.

I also know that kinetic heating effects of airspeed are not the answer (even though they may be a contributing factor at speeds above 200 kts) as slow light aircraft also lose ice in sub zero temperatures.

I suspect that it will have something to do with air friction in some way......

Can anyone help. The process is elluded to in so many places but never explained.

Cheers.

[Hand Solo]

To Jonny - in BA on the A320 and B744 fleets deicing makes no difference to the T/O performance. Same speeds regardless.

To TP - sublimation is a function of both temperature and pressure and I'm not entirely sure that it's the correct term for what occurs on airframes but I could be wrong. Sublimation occurs when a gas turns directly to a solid, or from a solid to a gas, without entering the liquid phase. My understanding of airframe icing is that it occurs either by contact of water with a sub-zero airframe, or super-cooled water with pretty much any airframe. In either case, the water is in liquid form thus has not sublimed into ice in the chemical sense. In the reverse I don't think the ice sublimes back into gas, it is simply that once icing conditions are left the ice melts due to friction from the airflow and is blown away in liquid form. I would speculate that is why a light, low speed aircraft will land encrusted after an icing encounter but a fast jet will be relatively clean.

[safetypee]

JF, IIRC Saab and ATR introduced changes which affected speeds, rotation, and climb schedules following investigation into the effects of thickened de-icing fluids (type 2 & 4). Other turboprop and RJ manufacturers conducted tests, and for those results I know of, there were either no effects from the de-icing fluids or the effects were within the existing performance tolerances. I wont’ mention types as all relevant information will be in the flight manuals.
I believe that the history of performance degradation due to the application of de-icing fluids was investigated many years ago and was based on early 737 aircraft. Although some small change in performance was detected it did not warrant any performance correction. One of the assumptions was that a high percentage of the fluid was blown off the wing before rotation; it is this area which has subsequently found to be in question for lower speed aircraft and when using the modern thicker fluids.
Refs
Air Dynamic Effects of Deicing/Anti-icing Fluids, Service Letter, Boeing Commercial Airplane Company, December 2, 1982. (Via AC-117 1982)
Transport Canada TP 13479E Contaminated Aircraft Takeoff Tests for the 1998-99 Winter.
ATR “Be prepared for icing” Oct 2003. Ref to FCOM 2. 02.08

[BOAC]

BA always applied a 'margin' on the reduced temp setting following de-icing on the 200 series 737 (I seem to recall 4 degrees?) but dropped it when the 200 left the fold and the Classic ignores it.