De-icing when there is no ice

[witchdoctor]

Completely baffled by this one. Why would the skipper want his a/c de-icing when the temp is +8 and dry, the a/c has been on the ground more than 1 hour, just been refuelled and there is no airframe icing? Is he having a silent protest of sorts, or have I been asleep in Met? :confused: No evidence of a cold soaked wing either.

[dicksynormous]

Why dont you ask him.As long as he isnt of the pompous type hiding behind his unquestionable divine command authority you should get a valid answer., and may even pick up a tip , or in the first case save a xmas card

[mutt]

If it happened to be a 777 operated by the national airline of a certain oil rich country, the answer lies in the amount of fuel that is getting tankered into the UK, however, upper or lower wing ice should be present.


Mutt.

[square leg]

It depends on the temp of the fuel in the wing, the temp of the fuel in the truck and whether or not the wing had frost/ice on it.

If the fuel in the wing is below 0°C and remains below 0°C after refuelling, any frost/ice that was previously on the wing isn't going to disappear that quickly even with +8°C OAT, unless removed "manually".

Basically "clean wing policy" applies. You may accept a thin layer of frost on the underside of the wing in certain areas.

Some okes just apply "procedure X" to all situations without adapting their mindset to the given conditions.

Tankering can become expensive when additional costs such as deicing come into play because of misjudgement.

But if in doubt, you can be rest assured that your wing was "clean" after deicing.:zzz:

edit:

Yes, as pointed out below, the dew point temp is significant as well.

[batty]

Should the fuel in the wing be below the dewpoint and also below zero the wing can suffer from non enviromental icing.

[None]

This type of icing was common when I flew the MD-80 series. Eventually the fleet was outfitted with heater blankets, solving that annoying aspect of the jet.

[Old Smokey]

Use of unnecessary Anti-Ice

Going a bit off topic here, but I well recall as a young First Officer a Captain telling a story AGAINST HIMSELF of using Airframe Anti-Ice when unnecessary.

He claimed to have been flying very high in very low temperatures, well below the iceing temperature range in cirriform cloud, where the only water present would have already been ice crystals. He turned on the Airframe Anti-Ice, and proceeded to ACQUIRE wing ice as a result.

His theory was that if left alone, the ice crystals would have bounced harmlessly off the cold airframe, but in turning on the Anti-Ice, melted them, whereupon the water ran back over the unheated portion of the wing, and froze.

I always thought it a good story, but doubted it's credibility over the past 30 years or so, I remain curious.

Can anyone lend any credibility or at least good theory to this story?

Anxiously awaiting a solution to a 30 year mystery,

Old Smokey

[witchdoctor]

All valid replies, thank you. However, none of the above applied here and unfortunately I wasn't in a position to be able to talk to the skipper directly, just sit and watch dumbfounded as his a/c (the only one that entire day) was de-iced in blazing (for December) afternoon sunshine.

Still mystefied, but I'm still the one on the outside looking in, so I guess he must have had his reasons.

[Notso Fantastic]

<Why would the skipper want his a/c de-icing when the temp is +8 and dry, the a/c has been on the ground more than 1 hour, just been refuelled and there is no airframe icing?>

I would assume he had tankered fuel in. Even at +8, there may have been ice underneath the wings- it can last longer than an hour. Topping up with warm fuel will not always clear it. He might have tankered a large quantity in of very cold fuel. It is possible to stay there for far longer than an hour. Instead of assuming nonsense like dicksenormous or questioning his sanity, it might be fair to just accept that the Captain may have had some justification to have asked for it!

[blackmail]

hello witchdoctor,

had a similar experience with a fokker 28 one day, long ago in lisbon during late springtime. oat+ 20°c, light winds, but overcast, unlike your story where it was a sunny day. landed with cold soaked wings after a 2hr30min flight at high altitudes. after refuelling & after the transit walk-around, it started to rain/drizzle slightly. well, within minutes the leading edges & underside of the wings were covered with icy river patches from the dripping precipitation. when i asked for deicing, the rampagent totally caught by surprise, answered:" no sir, not at this time of the year". so i showed him the leading edges. i don't remember the portugese traduction of "my gosh", or something alike. all we could do was to delay the return flight till the ice was melted. i still thank the lord for some kind of 6th sense that made me go out & check the wings when it started to rain.

and last but not least, witchdoctor, the fact that this captain was the only person asking for deicing that day, is in itself no argument whatsoever in either direction. as captain of your aircraft you have to decide the next course of action & not fall in the trap of being a follower of others. this does not mean that you must not look for what's happening around you, eg, on a dark & murky winternight i saw the opposite: several planes were deicing, i asked my f/o who did the walk-around if he noticed something abnormal on the wings concerning ice contamination? he replied by:"no, didn't notice anything wrong". again the 6th sense made me doublecheck & indeed nothing was visible in the dark, even with the torchlight, but by tactile feeling it was a complete different story: clear ice from the best quality, a few mm thick. never was so quick to ask for de-icing.

[alf5071h]

Old Smokey, some truth in the story. The long held theory is that in OATs of -40 C or colder there is insufficient free water to be an icing problem, all of the water would be ice crystals. What few ice crystals there were would indeed bump off the aircraft surfaces, thus de/anti icing was not required. Depending on the type of de/anti icing system, it could be possible to melt some crystals and get ice particles to stick on the surface with de/anti icing selected on in these conditions.

However, more recently, some aircraft have reported airframe icing in very low temperatures and rarely some engines and ice detection systems have suffered difficulties; ice crystals blocking tubes / overcome heating systems. The engine problems were associated with Cb anvils where there was a mix of water and ice crystals, the water became the glue for sticking crystals together. The particular manufacturer changed the definition of icing to include very low temperatures in the AFM and modified the engines.

[square leg]

Would that be the Allied Signal LF 507 RJ-1H perhaps?

[King Muppet]

Alexban

The possibility of encountering icing conditions after take-off is not a consideration of an anti-ice treatment. Most guidance on de-icing/anti-icing will contain warnings on this. See the AEA document: numerous notes along the lines of "De-icing/anti-icing fluids used during ground de-icing/anti-icing are not intended for - and do not provide - protection during flight."

I think someone has already commented on the fact that much of that fluid will have come unstuck by lift-off. Also a good reason not to sit too close behind another aircraft prior to take-off due to the jet blast effect on fluid.
--
Edit: think the comment on fluid separation must have been in another, similar thread.

[Beta-1]

King Muppet:

You are absolutely right, and it seems many pilots actually missed that point.

Type I-fluids (de-iceing) are designed to leave the surfaces as soon as any force is applied to them, like accelleration, wind, etc.

Type II and IV-fluids (anti-iceing) are pretty much the same as Type I-fluids, except that they have added thickening-agents and other various substances to the fluid, to make it more resistant to precipitation, and to make it stick better to the surfaces, and thereby give a longer lasting protection.

Basicly, as the aircraft approaches 80 kts, the anti-iceing fluids will start to come off the surfaces, and by 100 kts, the fluids will have left the surfaces, leaving only traces behind. The remaining fludis on the surfaces will give no protection what so ever.

The reason for designing the fluid to separate is because the fluid will cause unwanted changes to the aerodynamics of the wings. As the airspeed increases, the surface-tension of the fluid will keep the fluid from beeing blown off, but it will however be moved towards the trailing edge of the wing and horisontal stabilizer, altering the shape of said surfaces at the same time. This is until the airspeed of 80-100 kts is reached, and the surface-tension finally gives in and the fluids come off.

For this reason, anti-iceing treatments is only applied to aircrafts with Vr higher than a minimum of 80 kts. Some airlines use 100 kts for this limit.


Many pilots are not aware of this, and i have refused to give anti-iceing treatments to aircrafts where the commander insists on Type II-fluid, and the aircraft have been a slow-moving turboprop or piston-powered model.

Sure, it's his call to make, but as long as he shows no sign of understanding the aerodynamics involved in his decision, he's not going anywhere.


Blackmail:
You too hit the nail straight on the head! It's sometimes scary seeing commanders making their decision on wether or not to de-ice.

"Ohh.. The plane next to us didn't de-ice, so neither will we..."

The plane next to you may have been hangered all night, while yours have been outside accumulating ice on the wings and horizontal stab....

I've seen it happen, and as luck would have it, they were ok... The high-wing turbprop took off with 1-2 mm's of ice on the entire wing and tail. The de-iceing personell had left a warning for the crew, but they never got the message...

Some pilots do have a severe lack of knowledge when it comes to operating in winter-conditions, and would rather rely on gut-feeling and previous luck, than following SOP for contaminated wings...

It's scary out there boys and girls, but as luck will have it, they usually make it....

[safetypee]

Beta-1 your point “… and by 100 kts, the fluids will have left the surfaces, leaving only traces behind” is not completely accurate, see parallel thread here Icing and de-icing (http://pprune.org/forums/showthread.php?s=&threadid=154384). Quite considerable amounts of fluid can remain on the wing; however, your point about them giving no protection is correct.

Your reasoning about unwanted aerodynamic changes is partially correct; previously the industry had considerable concerns about this, but research showed that any reduction in aircraft performance was small (737). However, recent tests conducted by some ‘regional aircraft’ manufacturers suggest that there could be noticeable effects on climb performance, particularly if large quantities of fluid remained on the wing due to incorrect application etc. Furthermore, several turboprops have significant changes to operating procedures when using de-icing fluids; changes to take-off trim setting and take-off speeds; these were due to aircraft control problems.
In addition to the misuse of fluids, one reason for these problems could be the use of fluids with high ‘dynamic viscosity’ – the viscosity is proportional to airflow. As speed increases, the fluid will flow more easily, but if fluid moves into lower speed areas (flap gap, trailing edge, and control gaps), viscosity increases and it tends to stick and thus not all of the fluid comes off.

[TURIN]

Some years ago I was involved in the turn rounds of a er...Middle Eastern airline who thinks it is European....:suspect:

They seemd to have absolutely no idea of the necessary de-icing procedures. The station manager even suggested one day that I was in cahoots with the de-icing operator and receiving backhanders for each litre of fluid.

They could not grasp the concept of a cold soaked wing requiring de-icing even when it was 15+degrees (C) outside.

It was even worse when they moved on to the NG 737, the wing is thinner and upper surface ice was even more of a problem even after fuelling. Fortunately a refusal to sign off the a/c transit check stopped any further argument.

Witchdoctor, it is possible that previously melted ice had run down the underside of the wing and caused ridging which is usually a no-go.

As has been said, if the a/c commander, or any other person for that matter, believes that de-icing is necessary then best get on with it. There are far too many people pushing up daisies all for the sake of a few quids worth of glycol!!:ok:

[Shore Guy]

One of the recently discovered phenomenon of Type II and IV fluids is rehydration. After evaporation, a chemical residue remains that will “rehydrate” with water, but at the wrong ratio, resulting in a gel that can freeze.

Following from CAA:

REHYDRATION OF TYPE II AND TYPE IV DE-ICING/ANTI-ICING FLUID RESIDUES
Type II and Type IV Anti-Icing Fluids
The repeated application of Type II and Type IV anti-icing fluid may cause residues to collect in aerodynamic quiet areas, cavities and gaps. These residues may rehydrate and freeze under certain temperature changes, in high humidity and/or rain conditions. These residues may block or impede critical flight control systems and should be removed.

In order to limit these problems the repetitive use of Type II or Type IV anti-ice fluid should be avoided as far as possible.

When Type II and Type IV anti-icing fluid residue has been detected, no take-off should be authorized until the residues have been removed.

Recommendations
Operators should obtain guidance and instructions from the aeroplane manufacturer as to how to establish satisfactory procedures to detect and remove residues of dried fluid.
Operators should review their anti-icing procedures when using Type II or Type IV fluid,
amending their Operations Manual where necessary, to ensure the absence of residue, which could rehydrate and adversely affect the operation of the aeroplane. Procedures relating to a specific aeroplane type or operation should be promulgated in detail to all staff involved in deicing/anti-icing operations.

And from Boeing..

TYPE II AND TYPE IV FLUID REHYDRATION AND FREEZING
Last winter in Europe, restricted elevator movement interrupted the flight of two MD-80 airplanes. In both cases frozen contamination, a gel with a high freezing point, caused the restricted movement. The gel was Type IV fluid residue that rehydrated during takeoff or climbout in rain.
Rehydration can occur when thickened fluid is repeatedly applied in dry conditions, either to prevent frost from forming overnight or for deicing just before flight. The fluid dries out during flight, and a powderlike residue remains in aerodynamically quiet areas, such as balance bays and wing and stabilizer rear spars. If the airplane is not deiced or anti-iced during a subsequent layover and encounters rain on the ground or during climb, the remaining residue absorbs water and turns into a gel. The gel swells to many times its original size and can freeze during the next flight leg, potentially restricting the movement of flight control surfaces.
In the case of both MD-80s, the frozen gel restricted movement of the elevators, which are unpowered flight control surfaces on that model. Both flights were diverted, and elevator movement was restored when the gel unfroze during descent as the airplanes encountered warmer temperatures at lower altitudes. Inspection after the return of one of these flights revealed gel in the area between the elevator and elevator control tabs.
The issue of rehydration was discussed at the Society of Automotive Engineers (SAE) G-12 Fluids subcommittee meeting last May. The subcommittee also discussed related occurrences on other types of airplanes with unpowered flight controls and the deicing/anti-icing procedures used by the operators attending the meeting. These discussions led the subcommittee to conclude that the residue builds up when a one- or two-step deicing/anti-icing procedure is followed using Type II fluid, Type IV fluid, or both, in either neat or diluted form. This practice is prevalent in Europe.
The SAE G-12 Fluids subcommittee recommended including a caution note in the next revision of SAE ARP 4737 to address this issue. The SAE G-12 Methods subcommittee agreed and is including the following note in SAE ARP 4737D, scheduled to be released in late 1999.
CAUTION: The repeated application of Type II or Type IV, without the subsequent application of Type I or hot water, may cause a residue to collect in aerodynamically quiet areas. This residue may rehydrate and freeze under certain temperature, high humidity and/or rain conditions. This residue may block or impede critical flight control systems. This residue may require removal.