De -Anti icing 738
Thread Starter
Join Date: Apr 2001
Posts: 125
Likes: 0
Received 0 Likes
on
0 Posts
De -Anti icing 738
The issue I would like to discuss with you is regarding Anti-De icing
procedure.
The procedure itself is easy to understand but something caught my attention last winter.
There you are during the turn around time which may take from one to two
hours time . It starts to snow. It is moderate and heavy in some cases or it could be light / moderate freezing rain. Flaps are up.
During the waiting period the wings becomes all covered with snow and of
course some melts at the contact with the wing to freeze again.
Time is up and we have to DE ICE/ANTI ICE now. The truck comes and sprays the wing.
Ok here is the catch. Since flaps are up the LE are covering part of the wing.
If water ran underneath and froze my guess is that it won’t be removed or
probably only melted due to high temperature of the fluids used but not up to a 100%. Neither will that area be covered with a nice and even layer of ANTI ICE. I observed how big the area covered by the LE is and it is pretty big and in a very critical part of the wing.
Can anyone tell me more about this fact since I have not find any literature mentioning the matter. Should the DE ICING ANTI ICING be done with flaps down in order to uncover this area and make it subject to the same treatment as the rest of the wing?
If not properly De Iced and Anti iced once the flaps are extended for take
off, that area will be exposed to outside conditions making it vulnerable to
freeze or accumulate snow and therefore loose its performance.
Thanks
procedure.
The procedure itself is easy to understand but something caught my attention last winter.
There you are during the turn around time which may take from one to two
hours time . It starts to snow. It is moderate and heavy in some cases or it could be light / moderate freezing rain. Flaps are up.
During the waiting period the wings becomes all covered with snow and of
course some melts at the contact with the wing to freeze again.
Time is up and we have to DE ICE/ANTI ICE now. The truck comes and sprays the wing.
Ok here is the catch. Since flaps are up the LE are covering part of the wing.
If water ran underneath and froze my guess is that it won’t be removed or
probably only melted due to high temperature of the fluids used but not up to a 100%. Neither will that area be covered with a nice and even layer of ANTI ICE. I observed how big the area covered by the LE is and it is pretty big and in a very critical part of the wing.
Can anyone tell me more about this fact since I have not find any literature mentioning the matter. Should the DE ICING ANTI ICING be done with flaps down in order to uncover this area and make it subject to the same treatment as the rest of the wing?
If not properly De Iced and Anti iced once the flaps are extended for take
off, that area will be exposed to outside conditions making it vulnerable to
freeze or accumulate snow and therefore loose its performance.
Thanks
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
1) In winter, on t/round, the wings are normally sub-zero, especially NG
2) Extending flap on an untreated wing is dodgy - the LEDs may be frozen.
3) A certain amount of ice is allowable underwing.
2) Extending flap on an untreated wing is dodgy - the LEDs may be frozen.
3) A certain amount of ice is allowable underwing.
Join Date: Nov 2002
Location: Northern Europe
Age: 45
Posts: 152
Received 0 Likes
on
0 Posts
....but if you really want the covered areas treated with anti-ice, extending flaps/LEDs between first and second step in a two-step anti-icing is an option. I know it has been done...
All 737-operators i've encountered does not accept ice underwing, but up to 3 mm of frost...
3) A certain amount of ice is allowable underwing.
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
You are quite correct - the correct wording is 'frost'.
However, de-icing with flaps extended is not the recommended procedure for all the 737 operators I have known. Flaps are extended as late as possible before take-off to avoid contamination of the covered parts.
However, de-icing with flaps extended is not the recommended procedure for all the 737 operators I have known. Flaps are extended as late as possible before take-off to avoid contamination of the covered parts.
Join Date: Apr 2005
Location: Stockholm Sweden
Age: 74
Posts: 569
Likes: 0
Received 0 Likes
on
0 Posts
Just like to add something. When landing on contaminated runways some crews leave the flaps down for inspection. Having inspected flaps in the snow many times I would like to say that on B737 I see slush in the flaps behind the wheels, but on A320 B757 B767 B777 I have never seen anything. The wheelspray does not go up that far.
However if you have left the flaps down and it is snowing, then it is a good idea to leave them down until deicing has been accomplished. It is amazing how quickly snow covers them. There is no mention of this in our Ops Manual but if I have not inspected the flaps directly on arrival, then I leave them where they are until deicing finished, and then retract to take off posn. (but personally I think it is always better to retract them after landing)
However if you have left the flaps down and it is snowing, then it is a good idea to leave them down until deicing has been accomplished. It is amazing how quickly snow covers them. There is no mention of this in our Ops Manual but if I have not inspected the flaps directly on arrival, then I leave them where they are until deicing finished, and then retract to take off posn. (but personally I think it is always better to retract them after landing)
Join Date: Feb 2006
Location: Netherlands
Posts: 310
Likes: 0
Received 0 Likes
on
0 Posts
Non flying pax here...Please excuse me for posting here and move to SLF/spotters forum if more appropriate 
This thread has reminded me of something I noticed last winter on a 737NG...Saw what appeared to be a fairly thick build-up of ice on the wing root (approx area from engine pylons to fuselage, upper surface obviously, as seen from my seat) and wondered if this was normal/acceptable? No de-icing was carried out on this aircraft. Should pax bring things like this to the attention of crew, or would they check the top surface of the wing from inside the cabin prior to departure in freezing conditions as a matter of routine, assuming this part of the wing needs to be ice free?
This thread has reminded me of something I noticed last winter on a 737NG...Saw what appeared to be a fairly thick build-up of ice on the wing root (approx area from engine pylons to fuselage, upper surface obviously, as seen from my seat) and wondered if this was normal/acceptable? No de-icing was carried out on this aircraft. Should pax bring things like this to the attention of crew, or would they check the top surface of the wing from inside the cabin prior to departure in freezing conditions as a matter of routine, assuming this part of the wing needs to be ice free?
Join Date: Dec 2005
Location: UAE
Posts: 108
Likes: 0
Received 0 Likes
on
0 Posts
Perkin, non-environmental ice or NEI is quite common on the B737-800 and is caused by cold soaking of the wing during flight. It appears as a thin layer of frost on the upper surface of the wing and is common around the engine pylon and wing root. It can (in extreme cases) still be noted on the wing after landing in temperatures up to +18 degrees C!! This phenomenon is also common on other 737 series aircraft but normally only builds up on the under surface of the wing and not on the upper surface like the 800/900.
Usually if the ambient temperature is above freezing the layer will melt off itself. This rate of melting is greatly increased with the addition of warm fuel. Once melted the surface of the wing can be covered in condensation that can have the appearance of ice. Crews will actually go up a ladder and feel the upper surface to ensure that no ice exists (it it is suspected).
In most European countries the uppersurface of the wing must be clear of ice for departure. For this reason, if the NEI does not melt of its own accord then the wing must be de-iced (but not anti-iced). However, the US FAA has approved the B737-800/900 to depart with NEI so long as it is only formed within a black box painted on the uppersurface of the wing.
Hope this helps.
Usually if the ambient temperature is above freezing the layer will melt off itself. This rate of melting is greatly increased with the addition of warm fuel. Once melted the surface of the wing can be covered in condensation that can have the appearance of ice. Crews will actually go up a ladder and feel the upper surface to ensure that no ice exists (it it is suspected).
In most European countries the uppersurface of the wing must be clear of ice for departure. For this reason, if the NEI does not melt of its own accord then the wing must be de-iced (but not anti-iced). However, the US FAA has approved the B737-800/900 to depart with NEI so long as it is only formed within a black box painted on the uppersurface of the wing.
Hope this helps.
Join Date: Feb 2004
Location: West London
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
Should the DE ICING ANTI ICING be done with flaps down in order to uncover this area and make it subject to the same treatment as the rest of the wing?
If not properly De Iced and Anti iced once the flaps are extended for take
off, that area will be exposed to outside conditions making it vulnerable to
freeze or accumulate snow and therefore loose its performance.
Thanks
If not properly De Iced and Anti iced once the flaps are extended for take
off, that area will be exposed to outside conditions making it vulnerable to
freeze or accumulate snow and therefore loose its performance.
Thanks
Where freezing/frozen precipitation is falling between de-/anti-icing and take-off, SOP’s (should) require that deployment of flaps/slats be delayed until just prior to entering the active R/W. When extended at an early stage the newly exposed surfaces, which will not have a protective coating of de-/anti-icing fluid on them, will be vulnerable to the rapid build-up of snow/ice. This is of particular relevance where Type II and IV fluids, with their extended holdover times, have been used.
With regard to your concerns over snow melting, flowing forward between the fixed and moveable parts of the L/E and subsequently refreezing, would have thought this unlikely. The gap between them is minimal and I believe that there may be a seal on the underside of the moving part of the L/E to prevent this. Can anyone confirm this?
Join Date: Apr 2003
Location: Sutton
Posts: 564
Likes: 0
Received 0 Likes
on
0 Posts
Can't speak for the 737 but on several aircraft types anti icing with flaps / slats extended is prohibited. Can't recall the specifics but one type of anti ice fluid dries as a gel which then absorbs water. This water freezes in flight and (if the screwjacks etc were extended during anti ice) it prevents extension prior to landing.
Join Date: Aug 2001
Location: Europe
Posts: 117
Likes: 0
Received 0 Likes
on
0 Posts
, rendering our nice black markings totally useless 
Join Date: Nov 2002
Location: Northern Europe
Age: 45
Posts: 152
Received 0 Likes
on
0 Posts
Screwjacks is one thing, but rehydrated and subsequently frozen Type IV residue has a history of locking up the elevator inflight on some aircrafts (MD-80's and Dash 8 that i know of specifically)...
As far as i know, the use of Type IV has been abandoned in Scandinavia for this reason...
That beeing said, these things don't happen after a single anti-icing, but after many. The residues in aerodynamic quiet areas builds up over time, drying, rehydrating, freezing, over and over, until the amount of residue is enough to jam something when it's rehydrated and frozen, inflight...
Join Date: Apr 2005
Location: Stockholm Sweden
Age: 74
Posts: 569
Likes: 0
Received 0 Likes
on
0 Posts
The biggest problem for the supplier was getting the cold type IV to spread over the wing. It came out in globs, and would not spread to form a thin layer. Type II is much better in this respect, and the holdover times with the latest type II fluids are nearly as good as type IV.
You use the type II cold, as it cannot be pumped neat when hot without breaking down. Using it as anticing means that its temperature is not important.
