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Fuel icing (avgas)

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Fuel icing (avgas)

Old 7th Dec 2009, 14:29
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It's such a shame when seriously important flight safety matters get turned (yet again) into playground squabbles.

I can say for absolute certainty that it is not safe to fly an Aztec at colder than about -10C for any length of time without 1% IPA. If you do you are risking a double engine failure. I know this through painful experience.

IPA is a pretty unobtrusive chemical. It is the same stuff you stick in your ear if you have swimmer's ear (ie water trapped behind wax). It is kind to hoses, seals and bladders.

It is also pretty much exactly the same price as Avgas, if bought sensibly, so there is no financial loss.

The only disadvantage is that it is not easy to source locally so you have to carry it around, which is a fire risk.

But given the benefits of 1% IPA I just cannot see why people would take the risk of not using it.

And that has nothing to do with ego, willy size or whatever else you kids are chiding each other with.
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Old 7th Dec 2009, 14:35
  #22 (permalink)  

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eBay listing today or just search "Isopropyl alcohol 5 litres".
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Old 7th Dec 2009, 15:06
  #23 (permalink)  
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That's good value.

Does anybody know about the Aztec fuel system and what kind of fuel filters it has and how they are mounted?
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Old 7th Dec 2009, 18:38
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It is written in the manuals and one day an insurance guy may just come knocking on your door and deny a claim as you failed to adhere the manufacturer's data published in the POH.
Then cite the reference.

I said nothing about failing to adhere to manufacturer requirements. Show the requirement. Can you do that?

The Cessna manual cites a very specific, very unusual operating condition, and states as much...but identifies flight from a very humid location to a flight above 20,000'. Do you do this in your Cessna 414? I certainly wouldn't. I don't even generally operate a King Air 200 above FL200, let alone piston equipment. They don't do well up there, turbocharger or not.

You see, you keep on about "the manuals," but can't seem to quote them or cite the reference, and the only one we've been provided in this thread thus far relates to the use of lubricants and preventative maintenance in cold weather...which is, of course, irrelevant.

As you're unable, I shall, this from a Cessna 414:

Isopropyl alcohol may be added to the fuel supply in quantities not to exceed 1% of the total. Refer to the Fuel Additive paragraphs in this section for additional information.

Fuel Additive
Strict adherence to recommended preflight draining instructions as called for in Section 4 will eliminate any free water accumulations from the tank sumps. While small amounts of water may still remain in solution in the gasoline, it will nomally be consumed and go unnoticed in the operation of the engine.

One exception to this can be encountered when operating under the combined effect of: 1) use of certain fuels, with 2) high humidity conditions on the ground 3) followed by flight at high altitudes and low temperature (flightlevels of 20,000' or above and temperatures of -28.9 C or below). Under these unusual conditions small amounts of water in solution can precipitate from the fuel stream and freeze in sufficient quantities to induce partial icing of the engine fuel injection system.

While these conditions are quite rare and will not normally pose a problem to owners and operators, they do exist in certain areas of the world and consequently must be dealt with when encountered.

therefore, to alleviate the possibility of fuel icing occurring under these unusual conditions it is permissible to add isopropyl alcohol or ethelyne glycol monomethyl ether (EGME) compound to the fuel supply.

The introduction of alcohol or EGME compound into the fuel provides two distinct effects: 1) it absorbs the dissolved water from the gasoline and 2) alcohol has a freezing temperature depressant effect.

Alcohol, if used, is to be blended with the fuel in a concentration of 1% by volume. Concentrations greater than 1% are not recommended since they can be detrimental to fuel tank materials.

The manner in which the alcohol is added to the tank is significant because alcohol is most effective when it is completely dissolved in the fuel. To insure proper mixing the following is recommended...
This is, of course, what I stated at the outset. Fuel icing takes place in the tanks, lines, selector, and gascolator, filter, but generally not beyond that point in the engine fuel system. Such occurrences are rare and unusual, and not a problem in normal operations.

If one elects to use EGME instead of alcohol, then on should also pay heed to the caution regarding concentration and mixing, also found in the manual:

Mixing of the EGME compound with the fuel is extremely important because concentration in excess of that recommended (0.15 percent by volume maximum) will result in detrimental effects to the fuel tanks, such as deterioration of protective primer and sealants and damage to O-rings and seals in the fuel system and engine components. Use only blending equipment that is recommended by the manufacturer to obtain proper proportioning.

Do not allow the concentrated EGME compound to come in contact wit hthe airplane finish or fuel cell as damage can result.
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Old 8th Dec 2009, 18:20
  #25 (permalink)  

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EGME is unpleasant stuff and I wouldn't let it near my aeroplane.

It's all very well to talk about dealing with it carefully, but try doing that with a 40kt wind and a wind chill of -40. If IPA blows around it just evaporates, if EGME does it can write off the aircraft, not to mention the pilot.
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Old 8th Dec 2009, 22:32
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EGME (Prist) isn't that hard to mix. It's typically either tank batched by the fuelin vendor, or sold in 20 ounce cans. These spray like any aerosol can. A plastic delivery line clips on to the end of the fuel nozzle, the EGME is delivered into the fuel as the aircraft is refueled.

Anyone who deals with turbine equipment in the winter is familiar with the use of Prist.

I had several cases of EGME in cans several years ago, which lost their charge. We were in a part of the world in which obtaining the chemical was difficult, and we had to take what we could get. I ended up puncturing each can with a screwdriver, and pooling all the chemical in one dispenser for more efficient use. We attempted several garden spray devices to help deliver the chemical, but the seals and containers themselves became badly deteriorated in short order. In the end, it was all by hand.

This isn't common, however, and in most cases when using Prist, you'll never touch the chemical. I've had occasions over the years when it's sprayed back on me, and ended up on the finish and even in my face and mouth. It's never presented an issue so long as it's cleaned up, mouth washed out, etc. These occasions are rare. With the clip on the fuel nozzle, one simply depresses the button while fueling until the can is empty. The concentration is the same in avgas and turbine fuels, and is easy to calculate.

One can order it nearly anywhere that turbine fuels are sold, so most FBO's and fueling services will have access, and in most cases the fuelers will apply the chemical for you. Just not a big deal.
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Old 8th Dec 2009, 22:47
  #27 (permalink)  
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Why doesn't everybody use IPA when it works and is less hazardous?

Is there a difference between avtur and avgas usage?

Does any of the people here who seem to know everything about everything know anything about the Aztec fuel system?
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Old 8th Dec 2009, 23:01
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Isopropanol isn't available everywhere, and often Prist is easier to get.
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Old 9th Dec 2009, 14:31
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Looking for compatible bottle materials for IPA.

This (page 7) suggests that polypropylene should be fine. These look ok.

It would be somewhat embarrassing, or worse, if the container dissolved inside the aircraft
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Old 9th Dec 2009, 19:35
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Alcohol shouldn't be much of a problem in any containers such as you suggest. One should remember that it's a hazardous material (dangerous goods) and approach it accordingly when considering how to carry the chemical in the aircraft...especially in a passenger area or the flight deck/cabin.

If you're going to carry in a poly/plastic container, don't forget static and bonding issues. Much like one wouldn't want to carry or use a plastic fuel container on carpet or on a plastic truck/lorry liner, alcohol and other volatile chemicals must be taken into account as well.

EGME does considerably worse in many chemical-resistant containers, as we found out. We didn't carry it on board, but tried initially to store it that way for use during refueling. It didn't last long enough to complete the refueling, and even with a poly tank and a metal applicator, it still destroyed the seals inside the sprayer tank, fittings, and nozzle.

It's for these reasons that Prist in the can is a safer and easier means of carriage, than toting around a poly can full of IPA or other additive. The sealed cans of Prist discharge in the tank into the fuel stream at a metered rate, are fully self-contained and disposable, and take up very little room.
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Old 10th Dec 2009, 07:46
  #31 (permalink)  

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Prist is OK when delivered at the Avtur hose, I agree, but that is hard to organise for Avgas delivery. It may be safe to get in the mouth, but that's not what the HazChem descriptor says!

The answer to Peter's question is that EGME is required in much smaller quantities than IPA. For my trip over the Pole I had to carry 50 litres of IPA (enough for 5000 litres of fuel) because there was no chance of getting it in Svalbard, Eureka, Greenland etc. 50 litres is a lot of inflammable chemical to carry around, not to mention storage and weight.

However, the fact that I decided to carry 50 litres of IPA rather than 5 litres of EGME must say something!
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Old 10th Dec 2009, 13:33
  #32 (permalink)  
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OK, interesting. I can see carrying 1% of IPA could be a lot. I have been looking for containers (high density polypropylene - common as muck - is compatible) and it is slightly tricky given that no "plastic" container will be anti-static, and the pump man may be unhappy about you pouring the stuff in right under his nose, after all the earthing precautions which he is supposed to be doing himself. I asked this morning and would have to get permission from the head fireman. So obviously one would pour in the stuff before taxiing to the pumps, and then as the fuel is filled, that should stir up the tank sufficiently (or not?).

I would have preferred stainless steel containers but they are not easy to get with the right o-ring material, and chasing down o-ring chemical compatibility is more hours on the internet. It is a very specialist area. PTFE o-rings should be OK.

I have not even tried to look for compatible containers for the other stuff. The TB20 POH lists two options one of which is IPA; the other I can't remember.

But I am still waiting for details of the Aztec fuel system Having seen the underside of my TB20 I know what that looks like. Has anybody seen the underside of an Aztec? Where is the fuel filter, and what is it mounted onto?
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Old 10th Dec 2009, 15:14
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It may be safe to get in the mouth,
It's not, and nobody suggested that it is.

However, the fact that I decided to carry 50 litres of IPA rather than 5 litres of EGME must say something!
Yes, it does. It says you went about it the hard way and unnecessarily carried extra bulk and weight. That's your choice, of course.

Prist is OK when delivered at the Avtur hose, I agree, but that is hard to organise for Avgas delivery.
It's no more difficult to mix in avgas than isopropanol. I have no idea what an avtur hose is, but mixing Prist with an avgas hose is no different than mixing it when delivering kerosine. Clips onto the fuel nozzle, and done.

When delivering other methods, such as jerry cans or a wobble pump from cans, even slowly through a chamois cloth, delivery is still not a complicated process, and can be mixed in while putting the fuel into the tank, or tank batched in the cans prior to pouring; either way works.
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Old 10th Dec 2009, 17:41
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I carry a common or (more literally) garden watering can to mix the IPA with avgas before load into the tanks, and I am sure that the same method would work with EGME. The watering can has handy markings for volume, such that I can easily put two litres into a 200 litre tank.

Peter, I have been pouring IPA into fuel tanks from polythene 5 litre containers (as seen in the eBay link) into the watering can, thence into the filler for many, many years, in all circumstances from major airports to wobble pumps in the deep Arctic and no-one has ever even raised an eye-brow.

I suggest that just looking authoritative and just doing it is probably the answer.
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Old 10th Dec 2009, 17:42
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Epaulettes?
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Old 10th Dec 2009, 18:09
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Nah, steely eyes.
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Old 4th Jan 2010, 19:47
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FWIW I did a test flight today with 0.6% IPA in one tank and 0 in the other.

No measurable performance difference (measurement resolution ~ 0.5%).
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Old 23rd Jan 2018, 14:21
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Old thread but vital infos in here and a couple of misleading informations.

Out of the AFM / POH of Cessna 300 and 400 series twins:
"... and freeze in sufficient quantities to induce partial icing of the engine fuel injection system"

Continental and Cessna were aware of cases of fuel icing in high flying piston twins. They found out that fuel icing occurs in the fuel injection system, not in tanks or previous filters / screens. The finest filter, which is the last filter, is the one at the fuel flow divider = fuel manifold = fuel spider.

Due to it's 5.0 psi cabin differential pressure and high power output, the C421C is operated the most likely of all Cessna piston twins at well above FL200 and below -30 dC. That's why all C421C / Continental GTSIO-520-N produced in 1980 and after (trailing link gear facelift) were equipped with a heated spider and a retrofit kit is available for previous aircraft.

Sweet spot for the C421C regarding speed and economics for trips of more than 400 NM is FL250 (depending on wind). CHTs below 400 dF even during high summer and solid 220 KTAS @ 36 GPH (60 % MCP) at mid cruise mass. Those aircraft were built to fly high.
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Old 23rd Jan 2018, 14:56
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Well that's just solved a 40 year mystery for me.

I was a rookie air taxi pilot in the seventies and I lost an Aztec engine for no explainable reason in very cold freezing conditions. It ran perfectly the next day following a diversion!

No one taught me about, or even mentioned that fuel icing was a risk.
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Old 14th Apr 2022, 15:58
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Cessan 402 Double Engine power loss

My personal experience with fuel icing in Avgas occurred many years ago in a Cessna 402. Departure was from KTTD (Troutdale, Oregon) during the winter months. Weather on departure was the typical for western Oregon, cool and wet. The airplane had been parked outside for weeks but no water was found in any fuel sumps during preflight. The fuel was mixed with, what at the time, was the recommended amount of isopropyl alcohol. (Cessna later gave approval for our operation to double that amount after other similar incidents of power loss due to what was assumed to be fuel icing).

On this day everything was normal until about 30 minutes after reaching cruise altitude, (FL 230). I don't recall the exact OAT now, but it was well below ISA. The first indication of problems was a slow but steady rise in EGT on both engines. Turning on boost pumps and readjusting mixtures a couple of times did not stop the trend. Eventually the mixtures were at full rich with boost pumps on high, but the EGT's kept rising. A divert was initiated and shortly thereafter the right engine quit and was ultimately feathered. A couple of minutes later the left engine quit and I elected not feather it, due to the likelihood that once feathered it would not be able to unfeather due to congealing of the oil in the prop dome. The divert airport, (KDLS) was reached with just enough altitude to maneuver for landing. In the pattern the windmilling engine began to show signs of life but never developed useable power.

After letting the airplane sit for an hour on the ground both engines started and ran normally. No water was detected in any of the fuel sumps. We had no means of testing the fuel for water content, so just assumed that we had moisture in the fuel and topped off the tanks, mixing in Prist as no isopropyl was available. After a normal runup the flight departed and flew across country to Oklahoma with no additional problems.

I could relate an almost identical experience in a Cessna 340 that occurred within a few months of this incident.

We could never "prove" that fuel ice was the culprit, but all the indicators pointed that way and after we started doubling the amount of isopropyl in our aircraft we never had another problem.

The common features of both of these incidents were that both airplanes had been fueled in damp locations, (western Oregon/Washington). No visible water was ever observed in any of the fuel sumps. Both were cruising in the Flight Levels (low 20's) when the engines quit. But manifested in a similar manner, (as described above). Both ran normally after sitting on the ground for about an hour. Neither had any further problems after the concentration of isopropyl in the fuel was increased.

I've been away from GA for many years now, but I am skeptical when I hear pilots saying that fuel icing is not a concern in AVGAS.
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