Ice in fuel

[MyData]

Hi

I'm currently reading the excellent book 'The Killing Zone*' - a must read book for any PPL. Some of the articles are very informative, others highlight the incredibly poor decisions made by student pilots and those recently qualified.

There is a chapter on fuel management and one article got me thinking:

1. Does water in avgas freeze at 0C (or lower?)

2. If it does form ice, does the ice float or sink?

Based on my assumptions that ice will form, imagine the case where water has contaminated the fuel - by whatever means - and overnight it has frozen into ice in the fuel tanks.

A check for water in the tanks will draw clear fuel (assuming here that the ice has floated and so the bottom of the fuel tanks/pipes are clear of ice).

Would floating ice be easily visible during a visual check of the fuel tanks?

Following take off the temperature increases above the freezing point. The ice turns back to water and the water then leads to fuel starvation...

I'm sure this must have been discussed and documented many times in the past 100 years of flight - but I'm interested in any feedback on the importance of ice in the fuel system.

*The Killing Zone refers to the period from PPL qualification (when you are supervised) to about 350 flying hours. The majority of deaths in aviation occur in the group of pilots who are qualified to fly, but don't have the luxury of personal experience to draw on to prevent themselves getting into trouble.

[2Donkeys]

Your assumptions are more-or-less correct.

In my own experience if you have water in the bottom of your fuel tanks, this will indeed freeze when the temperature drops low enough. The effect is to block the fuel drains, making it impossible to get much more than a dribble out of them.


On the more general point about the period between 0 and 350 hours and the risk it carries, whilst it feels as though it should be correct, it does not tally with CAA stats.

2D

[CaptainMoore]

"On the more general point about the period between 0 and 350 hours and the risk it carries, whilst it feels as though it should be correct, it does not tally with CAA stats."

2Donkeys what are the CAA stats? As a low hours student pilot I would be interested to know.

[Mariner9]

Water will freeze, at as near to zeroC as makes no substantive difference. The the ice will not float on the avgas, but will form on top of any unfrozen water remaining in the tanks.

As 2D's says, frozen water should be apparent from blocked or restricted drains.

[2Donkeys]

You could do worse than to look at This publication by the CAA (http://www.caa.co.uk/docs/33/CAP667.PDF) if you want to see their GA accident stats and analysis.

2D

[CaptainMoore]

2D - Thanks for the link - very interesting reading.

Regards

Adam

[englishal]

I think they cite an incident in The Killing Zone where the tanks were checked before the flight, and no abnormalities were noticed. However, after departure, the large amount of water ice in the tanks (which had got in somehow) did melt, and caused the engine to stop....

[DragonflyDH90]

It would be quite feasible for this to occur in an aircraft with bladder style fuel cells such as a Cessna 182, 180 or perhaps a Chipmunk.
Where there is a ripple in the bladder and ice were to form, melting latter and finding its way to the fuel pickup, but it would be just as likely as a liquid.
With a wet wing tank or a solid tank as already mentioned it should be noticed with a blocked drain.
One thing that is worth noting is prior to commencing a preflight check it can be worth giving the wing or aircraft a reasonably firm wiggle to redistribute any water, hopefully to a drain point (make sure you give a reasonable time to settle).

[MyData]

Thanks for the reponses - and for the pointer to CAA document.

[skydriller]

One thing that is worth noting is prior to commencing a preflight check it can be worth giving the wing or aircraft a reasonably firm wiggle to redistribute any water, hopefully to a drain point (make sure you give a reasonable time to settle).

That is the one thing I have been told NEVER to do, and to check the fuel PRIOR to moving the aeroplane.....The drain points should be at the lowest points of the fuel system so any water collects there. Now, I know you said leave enough time for it to re-settle??

Regards, SD..

[DragonflyDH90]

If your that concerned about the time for any water to re settle just try a little experiment with a small jar full of fuel, add a little water and then stir like crazy. See how long it takes to settle out.

It doesnt take that long!!!! How long do you wait after re-fuelling before doing a water drain??? I bet not an hour.

As for drain points being at the lowest point of the system, this is generally true, but as I mentioned before there are a number of aircraft with rubber bladder style fuel tanks which over time begin to resemble a deflated ballon with all the associated ripples, water can collect in these ripples and it doesnt matter where youre fuel drain is it will never get to it...