low fuel temp Jet A

[hptaccv]

Hi,

just recently having had a problem with low fuel temp on a LAX-Europe flight (good ol Jet A mixture) a question arose.

We reached -38°c (40° being the published freezing temp for Jet A).
What would happen if one actually hit freezing temp on the fuel?
I wouldn't think that 50 odd tons of fuel would suddenly go solid. Water freezes from the top (anomaly of water) - what about fuel?
Depending on the placement of fuel/oil heat exchangers on differing engines, I would assume that 'fuel filter clogged' would probably be the first sign of more serious things to come.

Any ideas?

[aerobat77]

LAX-Europe flight ;)


ok.. afaik the "freezing point" is not the real freezing point like known from water but the minimum temperature the fuel is approved for . main limit is the viscosity usable for the pumps as well paraffin flocking in the filter which is bypassed then .

so put margins on it and answer yourself - nothing will happen when you go lets say -42 deg.

btw - jet a without any icing inhibitor is in nowadays very rare and when i,m right only used in usa anymore , mostly jet a1 with a lower minimum temparature contrailes the cold skies.

cheers !

[john_tullamarine]

Be very wary of differing fuel origins and spec variations. Search for information on Speedbird 38 .. very probably caught out by fuel waxing .. and there have been more than a few other incidents.

Having been involved on the tech side of an investigation into a similar event, I have read a range of relevant technical reports on the subject which suggest that the problem is one which warrants cautious consideration by pilots operating some susceptible aircraft (due to unfortunate fuel system design matters) or aircraft generally on long range operation in cold air masses. Quite a while ago now so I would have to dig deep to find the report on the particular event.

Your suggestion that fuel flow (or, perhaps, fuel quantity indication, depending on fuel tank arrangements) irregularities might be the first indication is consistent with what I have read elsewhere in the literature.

For the pilot's problem, it is not so much a matter of the fuel mass freezing as precipitating wax bodies which then tend to gum up the works, as it were. As the fuel temperature continues to decrease, the proportion of waxing grows ..

[hptaccv]

@john_tullamarine: ok. will do the search. thx!

@aerobat77: ..that's why I referenced the topic to an outbound-USA flight with simple JetA. Basically the topic only becomes one during winter on eastbound flights from the US westcoast to Europe.

[Fly3]

Jet A has a fuel freeze point of -40C but this a conservative figure. Having operated flights on a regular basis over the North Pole from the USA we had actual fuel freeze analysis done during refueling prior to each trip. The results showed that we were always safe down to -45C at least. The problem is, as stated, fuel waxing, and even when the temperature increases again the fuel may not return to it's original state and so fuel flow may continue to be adversely affected.

[hptaccv]

interesting.

The fuel freeze analysis done prior each flight - was that time consuming / costly? It would be interesting to know if the fueling companies can accomodate for this on request.

[Fly3]

Costly, probably, but if the information acquired prevents a descent to warmer air and a tech stop due to the increased fuel burn at that lower level, then worth it. Time consuming, no, done whist refueling is taking place, one sample at the beginning, one in the middle and one at the end. Results available almost immediately. No problem getting it done at LAX, JFK, EWR or BOS.

[fdr]

fuel mixing...

your problem is not just outbound... remember that the residual fuel contaminates the new uplift, and there is good guidance material available as to how long it takes to achieve the return to the single fuel quality. In practical terms, you remain contaminated, Jet A for the return. No one seems to really care, but there it is.

[john_tullamarine]

No one seems to really care, but there it is.

Except those folks and organisations who have been bitten by fuel waxing problems in flight ...

It is a REAL problem if the weather conditions and aircraft configuration put you in a bad spot.

We went far too close to having a splash one outcome .. saved only by the presence of a crewmember who had some familiarity with the background problem as it might present in that particular Type.

[JammedStab]

Details please....

......could prevent a future incident on a vague subject.

[john_tullamarine]

Sorry, not able to give too much in the way of details. However, generically -

(a) aircraft has a small section of the fuel system which is susceptible (ie somewhat exposed) to OAT variations

(b) longish flight at high level

(c) chilly air mass

(d) waxing caused a reduced fuel flow through the relevant bit and consequent downstream tank quantity alert (ie more going out from the downstream tank to the engine than coming in from upstream tanks)

(e) crew twigged that it was not likely to be a tank fuel loss problem but rather a fuel flow imbalance problem. Either way OAT was determined to be the likely culprit

(f) descended to a level where they could maintain cruise with reduced power settings until the wax dissolved (this descent, as you might suspect, was more in the nature of a programmed decision rather than a commanded action ..)

Problem - had they dilly-dallied at height trying to fault find, the waxed up region might well have gummed up totally and caused total fuel starvation to both moteurs with heart palpitations the likely result as they were over a watery area and a long ways from land.

[9.G]

a operator should have a rule in place for mixing the fuel types. If JET A is less than 10% of the total quantity after refueling with JET A1 than the freezing point corresponds to JETA1. Apart from that for the polar flight the operator usually operates fuel with additives to lower the freezing point and determines actual one which might be below the published by the manufacturer e.g JET A1 for A 330 published in limitations sections is -47C but the actual might be -50C.
However if no info regarding the actual FP is given before the flight then it's as per limitations. :ok:

[compressor stall]

Airbus have a pdf freely avaiable called Getting to Grips with Cold Weather Operations. http%3A%2F%2Fwww.smartcockpit.com%2Fdownload.php%3Fpath%3Ddo cs%2F%26file%3DGetting_To_Grips_With_Cold_Weather_Operations .pdf&ei=go64UMHqA4isiAfA8IDIDw&usg=AFQjCNGeY7EruAndJfk9Ww2XpjBgJuEiXg (http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDEQFjAA&url=http%3A%2F%2Fwww.smartcockpit.com%2Fdownload.php%3Fpath% 3Ddocs%2F%26file%3DGetting_To_Grips_With_Cold_Weather_Operat ions.pdf&ei=go64UMHqA4isiAfA8IDIDw&usg=AFQjCNGeY7EruAndJfk9Ww2XpjBgJuEiXg)

It has a section on fuel freezing and cold soaking. Worth a read.

[Brian Abraham]

Further to compressor stall, Boeing offers this

Aero 16 - Polar Route Operations (http://www.boeing.com/commercial/aeromagazine/aero_16/polar_story.html#3)

[galaxy flyer]

One might read the BA 038 report on fuel freezing. While rather specific to the B777 and RR engines, it does point up that fuel freezing (yes, waxing John) isn't to be trifled with.

GF

[chimbu warrior]

Some flight planning providers now incorporate a fuel cooling prediction chart/table for certain flights.