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On speed on profile
30th Jun 2008, 19:11
Trying to work out why a/c are deiced from front to back. Various searches on here and google have brought up de-icing procedure manuals but all I can find in them is leading edge to trailling edge and top to bottom. Can anyone give me any facts/ideas please as to why aircraft are de-iced from the front to the back.

Cheers

OSOP

gr8shandini
30th Jun 2008, 19:23
Top to bottom is common sense; just like washing your car. Front to rear may just be to help ensure that fewer ice particles re-attach themselves to the leading edge in the event that someone is less than diligent about their task.

Koan
30th Jun 2008, 19:25
It doesn't matter whether one begins from the top the bottom the left or the right. The holdover time for deicing MUST begin at the the time of the first point of application of deicing fluid. (Our airline uses the right wing root for purpose of standarization).

Joetom
30th Jun 2008, 19:52
Aircraft are designed to allow air/fluids to pass front to back as a general rule with as little problems as possible.

Moving air or fluids from back to front can cause many many problems.

One that comes to mind is pushing some ice into places that you may not want it.

Green-dot
30th Jun 2008, 20:59
This is how we do it:

Top to bottom, front to back and from wingtip to wing root.

Top to bottom: requires less deicing fluids and gives a better view on the to be treated surfaces such as the vertical stabilizer (less steam to hinder the view when starting from top to bottom). Also reduces the chance of flooding the APU inlet. On the fuselage, deicing fluid is sprayed above the cabin window line which will then drip downward. This prevents spraying directly on to the windows which should be avoided, same goes for the cockpit windscreen and windows.

Top to bottom: also prevents spraying onto pitot tubes, static ports or ram air scoops on the lower half of the fuselage which should be avoided for obvious reasons.

Front to back: to have a good overview on the wing (and stabilizer) leading edges and forward, most critical area of the wing. Also better to manage application of deicing fluids using the leading edges as a reference. A good application technique is to cover the leading edge and upper surface of the wing with a minimum amount of fluids dripping on the tarmac from leading- and trailing edges. Spraying fluids from aft to front over the wing does not give an acceptable view on the leading edges and a lot more fluid will drip from the trailing edge than necessary. Also spraying from aft to front over the wing risks more fluid entering the "quiet areas" such as speed brake/lift dumper cavities and trailing edges with cable runs. Residual deicing fluids in "quiet areas", turn into a gell over time which may negatively affect flight controls. Also a higher risk of damaging static discharger wicks on trailing edge surfaces when spraying from the back to front (spray nozzle closer to the dischargers).

From wingtip to wing root: gives a better overview manouevring toward and around engine nacelles and toward the fuselage. Due to wing dihedral on most aircraft types, less fluid is required because there is better control over the fluid path flowing toward the lowest point, the wing root, which is always in view spraying from tip to root.

Furthermore, on remote spots, we direct aircraft position depending on wind direction. When ever possible we put the aircraft with the nose into the wind so any spray will go from front to back.

Regards,
Green-dot

planett
1st Jul 2008, 03:23
And just perhaps........the representative surface is the first treated and holdover timing starts then. I would assume the representative surface must be visible from inside the aircraft in most jurisdictions, preferrably from the flight deck. (not always possible) This will be the first surface to become contaminated again when a long taxi is threatening.

Theoretically, if this surface is fine, all the others are too. A representative surface is often the wing leading edge.

MarkMcC
1st Jul 2008, 03:39
Absolutely correct - having conducted anti-icing certification trials myself this was a prime consideration. The pilot must generally have a clear view of the 'controlling' area for holdover, and this area must be de- or anti- iced first as that is when the holdover clock starts. Inner wing root on the pilot's side is the preferred spot for the first application of anti-icing fluid when a two-stage decontamination is performed. Nothing aerodynamic here, just a practical operational consideration.

On speed on profile
1st Jul 2008, 15:59
All very good inputs thanks for the help.

OSOP

Green-dot
2nd Jul 2008, 20:09
@Planett,
And just perhaps........the representative surface is the first treated and holdover timing starts then. I would assume the representative surface must be visible from inside the aircraft in most jurisdictions, preferrably from the flight deck. (not always possible) This will be the first surface to become contaminated again when a long taxi is threatening.

Theoretically, if this surface is fine, all the others are too. A representative surface is often the wing leading edge.

@MarkMcC,
Inner wing root on the pilot's side is the preferred spot for the first application of anti-icing fluid when a two-stage decontamination is performed. Nothing aerodynamic here, just a practical operational consideration.

Often not practical to check for the flight crew because of poor visibility from within the cabin due to contaminated cabin windows (with anti-icing fluids), precipitation on the windows or darkness. Judgement from the flight deck due to the distance to the wing is often also not practical in light of the "clean aircraft concept."

A reference surface can be appointed if only one de-icing truck is involved in the operation (usually gate de-icing) but deicing on remote spots usually involves 4 trucks operating simultaneously.

That is why overhere the de-/anti-icing supervisor is in charge of the de-/ anti-icing operations and post treatment inspections. The supervisor notes at which time the first area is treated with anti-icing fluid (single step anti icing or during 2 stage de-/ anti-icing: the 2nd stage). That is when the holdover time commences and this time is reported to the flight crew together with the concentration of the anti-icing mix.

The supervisor reports when he/she has completed the post treatment inspection of the wing and other critical surfaces (some aircraft types require a tactile (hands on) inspection). Often a black stripe is painted on the wing leading edge and wing upper surface (at approx. 75% span along the wing chord) so the flight crew can check from the flight deck for contamination during the holdover time while taxying to the runway for take-off.


Green-dot

Admiral346
2nd Jul 2008, 21:06
Man, it's JULY!

You are really doing searches on the net for deicing in July?

I know, not a productive input...

nic

VinRouge
3rd Jul 2008, 03:30
I was always told its a good idea to offload the stab first, (or tailplane dependent on type) to prevent tipping the aircraft, especially if you are already a little taily... Sure an inch or two wouldnt make a difference, but I have seen up to a foot of wet, heavy snow on tailplanes before and wouldnt mind hazarding it could tip the aircraft if there wasnt much in it...

Then again, I am probably talking hoop, so please ignore me! :ok: