Honest De-Icing Question

[thirdtimecharm]

Hello,

I just wanted to be clear- we weren't asking why the other guys aren't de-icing, but rather why are we deicing.

We get the call long before the flight is on the ground- sometimes before it has taken off to arrive here.

I really don't think that the other guys are being unsafe at all... just a difference in SOPs that we were curious about.

[pdw]

We get the call long before the flight is on the ground- sometimes before it has taken off to arrive here.

That is a good way make real sure their destination de-ice crew is on standby. The other 737-200 crew by the way ... would simply follow suit if the outlook turned worse ?

Is there a cancellation charge / call out charge when the service is pre-ordered and then called off due to slightly warmer (or much colder) conditions than expected ?

That is an effort in good communication to call it in "long before". From what was implied earlier about ordering a de-ice ahead of time when it's slightly obvious there's a good chance it's not necessary, this crew is likely just setting it up so they're eliminating any chance to get into downtime on account of any mis-communication at their end (you also mentioned they can be really touchy about it when questioned). It's still early in the season and the de-ice/anti-ice procedure might not be quite as routine as when that job becomes the everyday / rehearsed event in the fall.

[pdw]

None of us have ever been on an aircraft down south that de-iced when it was +15 on the ground.

On occasion this summer, even in July, I noticed the aviation weather temperature map showed minus five degrees out over the water East of Rankin, when just a few miles West, inland of the port, it was very warm; an unusually steep temperature gradient over a relatively short distance.

It's true we won't see that extreme "down south" here with summer temps near the freshwater lakes (ie Erie and Ontario) .. 'cepting maybe with warming weather very early in spring, which can once-in-a-while chill down far enough / so quickly from 10-15 degrees as a briskening moist lake breeze out of the North changes just a bit from NNW to NNE, and just as the sun has disappeared behind cloud.

OK, great topic; now to carry on with discussing variances in SOPs / culture ...

[thirdtimecharm]

Strangely enough we ended up doing our recurrent de-icing training this morning (not the jet operator's training) and we discussed this a bit.

As the jet operator's machine takes 45+ minutes to warm up, we proactively get it going about an hour prior to arrival regardless if we have received the call.

Couple of the guys who sprayed for the jet operator have said they were told that we have to spray if the fuel tank temperature is showing below 0 degrees celcius, regardless if there is visable frost/ice. This doesn't seem to be an SOP but rather a pilot preference issue. This is why we had to deice in +10... no frost but a tank temperature reading below zero.

The many aircraft wreckage photos have reminded us not only to not question the pilot's decision, but to try and smile no matter what the request involves

Be safe and have fun!

[pdw]

De-icing on a sunny +10°C day. Can't say I have ever had to do it and wouldn't even bother to check the top of the wings on such a day. I wonder if there are even de-icing guys around at most southern airports when it goes down to 10°C at night.

Just for the record .. this appears to be daytime/mid afternoon and the +10C disappears with the sun hidden behind cloud .. +8 ... +7 ... + 6

[pdw]

So how do you explain this part of a post from what appears to be a person with de-icing training....

"We have had to de-ice several times in what has been our warmest summer in a long time, even when it was over 10 degrees on the ground and there was no visible ice on the wing."

It's starting to come through a bit more clearly if we're seeing rain occasionally freezing at plus 7 Celsius onto a quickturning aircraft's upper laminar surfaces next to the fuel storage; and doesn't sound like it will always be easy to tell whether the falling precip at the time is supercooled already or not ...ie how far is the cooling process advanced thru H20 phase-change (the huge heat-loss that must occur at a steady zero-C before ice happens). The pavement all around the taxiing aircraft is sometimes warm, relatively, and not obvious from a flight-deck when rain is getting that cold ... to elude the anti-ice strategy of even the most watchful crew. So in the case where a crew then orders it for the sake of 'not taking any chances', it stands to reason that 'safer' decision can actually look weird to someone not privy to all pertinent detail the pilots determine while flight-planning.

EDIT: Of course here we were just exploring how the 'corrollary of events' around the simple concept of "cold soaking" might perplex even the best of them just a little (the de-ice crew themselves for example) when on a warm day an order is given ...

[GyvAir]

It's starting to come through a bit more clearly ...

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[GyvAir]

http://www.tc.gc.ca/eng/civilaviation/p ... ry-203.htm

1. As discussed in Chapter 1, a very small amount of roughness, in thickness as low as 0.40 mm (1/64 in.), caused by ice, snow or frost, disrupts the air flow over the lift and control surfaces of an aircraft. The consequence of this roughness is severe lift loss, increased drag and impaired maneuverability, particularly during the take off and initial climb phases of flight. Ice can also interfere with the movement of control surfaces or add significantly to aircraft weight as well as block critical aircraft sensors. There is no such thing as an insignificant amount of ice.

2. Ice can form even when the outside air temperature (OAT) is well above
0°C (32°F). An aircraft equipped with wing fuel tanks may have fuel that is at a sufficiently low temperature such that it lowers the wing skin temperature to below the freezing point. This phenomenon is known as cold-soaking. Liquid water coming in contact with a wing, which is at a below freezing temperature, will freeze to the wing surfaces.

3. Cold-soaking can be caused by fueling an aircraft with cold fuel. Where fuel tanks are located in the wings of aircraft, the temperature of the fuel greatly affects the temperature of the wing surface above and below these tanks. If there is rain or high humidity, ice can form on the cold-soaked wing and accumulate over time. This ice can be invisible to the eye and is often referred to as clear ice. Cold soaking can cause frost to form on the upper and lower wing under conditions of high relative humidity. This is one type of contamination that can occur in above freezing weather at airports where there is normally no need for deicing equipment, or where the equipment is deactivated for the summer. This contamination typically occurs where the fuel in the wing tanks becomes cold-soaked to below freezing temperatures because of low temperature fuel uplifted during the previous stop or cruise at altitude where low temperatures are encountered, or both, and a normal descent is made into a region of high humidity. In such instances, frost will form on the under and upper sides of the fuel tank region during the ground turn-around time, and tends to reform quickly even when removed.

4. After a flight, the temperature of an aircraft and the fuel carried in the wing tanks may be considerably colder than the ambient temperature. An aircraft's cold-soaked wings conduct heat away from precipitation so that, depending on a number of factors, clear ice may form on some aircraft, particularly on wing areas above the fuel tanks. As well, cold soaking can cause ice to form due to humidity in the air when there is no precipitation, even when the temperature is above freezing. Such ice is difficult to see and in many instances cannot be detected other than by touch with the bare hand or by means of a special purpose ice detector such as a Ground Ice Detection System (GIDS). A layer of slush on the wing cannot be assumed to flow off the wing on takeoff and must be removed. This layer can also hide a dangerous sheet of ice beneath.

5. Sheets of clear ice can dislodge from the wing or fuselage during takeoff or climb and can be ingested by aft fuselage mounted engines, thereby damaging or stopping them and can also cause impact damage to critical surfaces such as, the horizontal stabilizer.

6. The formation of contamination on the wing is dependent on the type, depth and liquid content of precipitation, ambient air temperature and wing surface temperature. The following factors contribute to the formation intensity and the final thickness of the ice layer:

low temperature of the fuel uplifted by the aircraft during a ground stop and/or the long airborne time of the previous flight resulting in a situation that the remaining fuel in the wing tanks is subzero. Fuel temperature drops of up to 18°C have been recorded after a flight of two hours;

a large amount of cold fuel remaining in the wing tanks causing fuel to come in contact with the wing upper surface panels, especially in the wing root area;

weather conditions at the ground stop, wet snow, drizzle or rain with the ambient temperature around 0°C is very critical. Heavy freezing has been reported during drizzle or rain even in a temperature range between +8°C to +14°C.

7. Skin temperature should be increased to preclude formation of ice or frost prior to take-off. This is often possible by refueling with warm fuel or using hot Freezing Point Depressant (FPD) fluids, or both.

8. In any case, ice or frost formations on upper or lower wing surfaces must be removed prior to take-off. The exception is that take-off may be made with frost adhering to the underside of the wings provided it is conducted in accordance with the aircraft manufacturer's instructions.

9. Aircraft certified for flight in known icing condition have been designed and have demonstrated system capability of providing some protection against the adverse effects of airframe icing in flight only. In addition, stall warning systems only give an effective warning under clean wing conditions.

10. Frost, ice or snow formations on an aircraft may decrease the lift and alter the stall and handling characteristics. Aircraft may become airborne in ground effect but be unable to climb.

[pdw]

In the above 10 points, #2,#3,#4 & #6 all apply directly to this particular discussion thread, how ground icing in very warm temperature is caused or aggravated ... by cold soaking of fuel content inside the fuel tanks of a wing structure.

Not sure how reliable it will be, just when needed, to have adequately warm fuel on hand or a way to warm it, then to add it in the right quantity to an aircraft's fuel supply during a quick turnaround to moderate fuel temperature adequately ... as pointed out in #7.

[GyvAir]

As far as feasibility of raising the temperature by adding warm fuel, that would depend a simple function of the temperature and quantity of the fuel added relative to the temperature and quantity of the cold fuel already in the wing.
Attempting to significantly raise the surface temperature of a wing full of cold fuel using hot deicing fluid as they suggest in #7 doesn't sound realistic to me, regardless of time available.

[pdw]

Agreed, the heat from a brief fluid application can't do anything for a cold-soaking; hope that suggestion is corrected or at least disclaimed for the 'wet wings'. A film of anti-ice fluid applied onto a substrate after de-icing the fuel frost first, isn't much, yet obviously creates a small window where the sub-zero metal's continued gathering of frost holds off a bit ... enough to become airborne and achieve some greater altitude/speed. The warmth of that wee amount of fluid definitely can't touch a cold-soaking if the tanks are topped or nearly.

Seeing the futility of trying to quickly moderate a deeply cold-soaked fuel supply in that manner comes with experience, and some operators/crews will see that type of issue more than others.

[GyvAir]

Actually, reading over that particular page of the publication again, it's a summary of issues and causes related to wing icing in general, not just cold soaked fuel icing, so the wording of #7 isn't necessarilly altogether out to lunch.

[co-joe]

Pretty easy to figure the whole equation out. One company cares a whole lot more about a culture of ering on the side of safety. The other cant seem to learn from their mistakes and is therefore in the process of being purchased by the one with a culture more conducive to a long prosperous and safe life.

I know which one I'd put any of my loved ones in a seat on, and which one seems to make headline for all the wrong reasons.

[pelmet]

Pretty easy to figure the whole equation out. One company cares a whole lot more about a culture of ering on the side of safety. The other cant seem to learn from their mistakes and is therefore in the process of being purchased by the one with a culture more conducive to a long prosperous and safe life.

I know which one I'd put any of my loved ones in a seat on, and which one seems to make headline for all the wrong reasons.

Seems more like one company(or a couple of PIC's) is de-icing unnecessarily because of a misunderstanding by either the pilots or whoever is authorizing SOP's directing the pilots.

If you actually believe your statement, I assume that you are avoiding virtually every other carrier in the world as they would be unsafe as well as they are not erring on the side of safety either.

[pdw]

The question here seems was with regards to the anti ice application, as to why in the specified context (the initial post of this thread) the two identical aircraft had one crew request it but not the other ... at a similar departure time.

No mention of an actual de-ice requirement (no ice anywhere on either aircraft), ... I suspect just a chance for catching some after take-off in the early altitudes ?

How long is that shot of anti-ice fluid going to be useful anyways in a case like this ?

[Donald]

No mention of an actual de-ice requirement (no ice anywhere on either aircraft), ... I suspect just a chance for catching some after take-off in the early altitudes ?

Couple of the guys who sprayed for the jet operator have said they were told that we have to spray if the fuel tank temperature is showing below 0 degrees celcius, regardless if there is visable frost/ice. This doesn't seem to be an SOP but rather a pilot preference issue. This is why we had to deice in +10... no frost but a tank temperature reading below zero.

Hahahahah.....thanks for the chuckle!

[pdw]

Sure, nice catch.

By the time airborne, the humidity-generated fuel frost can no longer re-generate at that temperature under the higher (melting) airspeed.

Judging the 'to spray or not to spray' by fuel temperature (below or above zero C) is actually the simplest way to base that decision for a SOP. A sure way the pax don't see cold-soaked freezing before the take-off.

[FICU]

As the jet operator's machine takes 45+ minutes to warm up, we proactively get it going about an hour prior to arrival regardless if we have received the call.

We look at fuel temperature in cruise and temp/dewpoint at the destination airport to decide if we think we will have to de-ice. While in cruise we advise ops to have the de-ice equipment ready if we think there is a chance we will have cold soaked fuel frost on arrival. If we don't have any frost then we don't spray but having it warmed and ready and not using it is better than having to take a long delay to get it warmed up after we land and we find we do need it.

Couple of the guys who sprayed for the jet operator have said they were told that we have to spray if the fuel tank temperature is showing below 0 degrees celcius, regardless if there is visable frost/ice. This doesn't seem to be an SOP but rather a pilot preference issue. This is why we had to deice in +10... no frost but a tank temperature reading below zero.

This is most definitely not an SOP and is a waste of money and resources.

[Donald]

Pdw: since I'm not sure you're a pilot, you do realize the difference between ground icing and airborne icing, right?

[pdw]

"Ground" is up until rotation; yet any ground material taken along into a rotation, for whatever reason, stays that until melts or wears away or is covered over by airborne catch up ahead in climb / enroute.

Catch collected after rotation with 'clean concept' is all "airborne ".

At the next destination though ... any ice-catch on laminar surfaces resorts back to being "ground".

[Donald]

Right. So there's no need to make this complicated. If it's clean on the ground, no spray. If it's contaminated, unless it's fuel tank frost and you are WestJet or have the magic wings mod, you must spray.

[pdw]

It's not really that special a pass (the aforementioned exclusion of WJ), as it allows no more than 1/16" on a limited area of upper surface within the "designated black lines"; and not O.K. if one wing has more area covered than the other, or the ambient temp dips below zeroC for takeoff, or when departing in visible moisture/precip with less than a mile VIS.

Not many reports on record of crashes attributed to fuel cold-soaking. Pelmet mentioned one (an MD-80 on the previous page) and I know a report from ten years ago that has some evidence in it of a cold-soaking contribution, but not actually mentioned there-in; can't expect it to be included in the 'findings as to risk' column when still too uncertain to determine it a factor, or how to go about researching it accurrately. So, looks like not a whole lot of solid history on this accident risk-factor available as far as reports are concerned, considering the frequency of cold soakings.

[pelmet]

Not many reports on record of crashes attributed to fuel cold-soaking. Pelmet mentioned one (an MD-80 on the previous page)

That specific case would not have caused a 737 crash as it has to do with ice breaking off from the top of the wing and entering the engines of the MD-80.

Which is why you might not want to let ice accumulate on the leading edge in flight prior to selecting anti-ice on for an aircraft with tail mounted engines. Preferred to have the heat on prior to accumulation(although it is not always done that way). It may be OK for some wing mounted engine jet aircraft to let the ice accumulate prior to heating but of course the engines are ahead of the wing leading edge.

[pdw]

Which is why you might not want to let ice accumulate on the leading edge in flight prior to selecting anti-ice on for an aircraft with tail mounted engines.

No, wouldn't have thought that steady (thinner) shedding could take those big engines out. I wasn't able to find if ever determined what actual size/# of ice pieces actually got into the engine, just says that at least one might have kept going had the pilot(s) been fully versed on the thrust management system, which re-applied a higher power setting again (right after it was cut back intentionally after ice ingestion) to prolong the engines at lower / less-destructive rpm ... less vibration for any out-of-balance components.

[sstocker31]

I think we should all just stay on the ground and drink coffee.....much safer that way.