Dear friends and followers welcome back to my channel and to an interesting video and a rare
technical video about freezing fuel we'll be talking about jet fuel
characteristics, how to actually prevent fuel from freezing up and
A crash that resulted from freezing fuel a few years back. This is going to be a very cool topic
So let's get started!!!
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Nowadays when you board a plane you expect to safely get from A to B and as fast as possible
Please, but many passengers still worry about an engine or pressurization failure
But hardly anyone questions freezing fuel.
well
Thankfully no one really has to primarily because of this part of equipment which is installed on most jet airliners
But I'll come back to that in a minute now to simplify this video a little we'll assume that car diesel has very similar
characteristics as jet fuel now flammable liquids such as diesel have
four important temperature values
The auto ignition point the temperature so hot that the liquid will self ignite. Then the much lower
Flash point, the temperature at which vapor would ignite if you add some flame to it.
Then the cloud point at which the liquid slowly becomes cloudy meaning particles are
Starting to freeze up and last but not least the so called pour point at which diesel slowly starts to solidify
Into a crystalline state giving it that wax or gel look-alike texture
Now if your country is on this list right here
You might have heard of winter alpine or even Arctic diesel now, now what's that?
Let's say you were to live in Germany. These are the diesel cloud points
you would be dealing with, now the summer diesel with a fairly high cloud point temperature
now if you were to get any colder close to the pour point the fuel would clog up your filter or injection system at
those temperatures now without knowing as soon as
temperature becomes lower towards winter the petrol stations then fill up their tanks with winter diesel with a much
Lower cloud point of minus 20 degrees. So your car doesn't suddenly stop on the German, Autobahn.
That means the winter diesel is chemically treated to lower its Cloud point and there is a country which sells
diesel with a cloud point of minus 50 degrees comment below if you think you know, which country that is
It is not Canada, by the way
So, how does this relate to jet
airliners? Now commercial jet fuel or commonly known as kerosene is split up into three major players
Jet A-1 available outside of the U.S.
Jet A which is only available in the U.S. and in much more rare jet B
Which is primarily used in military aircraft and to be found in northern, Canada, Alaska and sometimes Russia
because of its low freezing point. Now I said freezing point
the freezing point is
similar to the cloud point the jet fuel becomes cloudy and if it gets any colder
approximately six degrees less than the freezing point it
solidifies to wax. Now write this down as this is a common question in your ATPL theory exam
What is the freezing point of jet A-1?
minus 47 degrees
So it is much lower than your average diesel fuel from the petrol station and to all my American followers
Yes, it is called a petrol station. I don't know why you call it a gas station
99% of your cars run on a liquid not on a gas
So as the wing tanks of the jet airliner are being refueled, the fuel commonly enters at outside air temperature now
Let's say 20 degrees
Depending on where you are and how cold it is
fuel sometimes can be preheated before being filled into your wings.
So as the plane then takes off and climbs to cruising level
Let's say to flight level 3 6 0 the outside temperature
plummets to a chilly minus 56.5 degrees and lower
so over time the fuel will cool down as the jet fuel is in direct contact with the metal for example the wing
Which is exposed to the freezing outside air temperature and tests have shown that the cooling rate can vary
From three degrees to twelve degrees per hour in severe conditions
So let's quickly look into how fuel temperature is being measured
now on the Boeing 747 the fuel tank temperature sensor is located
In main tank one
Do you have any idea why it's located specifically in that tank
Now as the outer part of the wing is much thinner
It has a low surface to volume ratio
Meaning the fuel tank profits less from the thermal friction of over passing air
Then the tank near the wing root plus their volume is much smaller
So a small pond freezes up much quicker than a large lake
Now another very important indicator to monitor
The fuel temperature is the total air temperature gauge right here. Now what is the total air temperature?
Now the very simple answer it's the airplanes
surface temperature which generally is warmer than the SAT, the static air temperature now the
TAT is the result of the static air temperature and the Mach number
You can very often see it's probe placed at the forward part of the fuselage
So as a pilot you are advised to monitor the fuel temperature gauge from time to time
now other than that, in case the fuel temperature reaches
minus 37 degrees on the 747 the ICAS message fuel temp low is triggered. Now why is
minus 37 degrees the trigger for that warning? Minus 37 degrees is three degrees prior
freezing point of jet A
which is only sold in the States and Boeing being an American based company they want you to take action
Once that warning pops up before the fuel gets any colder.
So what do you do as a pilot if that message appears? Now funny enough
You would have to check the fuel receipt where you have last
Refueled your plane jet A-1 in your tanks meaning your freezing point is at minus 47 degrees
So at that point nothing really to worry
but you would have to time the
Decrease in fuel temperature and compare to the remaining flight time to not make the situation any worse
Now a very important statement here
But what if the plane was recently fuel in the States with jet A and then mixed with some jet A-1 fuel from Europe?
You would have to consider the higher freezing point of minus 40 degrees for the time being
Boeing recommends only after three consecutive jet A-1 refueling stops
You could use the lower freezing point of minus 47 degrees
Makes sense, right? So you see there is a potential risk
especially on long flights routing near the polar areas that fuel freezes or
Turns into a sluggish waxy jello state clogging up the fuel lines
Decreasing the engine output or even worse letting the engine flame out.
So what can you practically do as a pilot to avoid your fuel from freezing up?
Now the in-flight procedure
recommends primarily to closely monitor the indicated fuel temperature and the total air temperature as there difference is
your main indicator for further actions. Step 1 and you might think I'm joking, increase your speed
Yes, increasing your airspeed will have an impact on your fuel temperature now
but how? Flight tests have shown that only
0.01 Mach increase in speed will raise the total air temperature
respective the fuel temperature by
0.5 to 0.7 degrees
I personally find that quite impressive that just that little
increase in airspeed creates so much more air friction and so raises the total air temperature fuel temperature
But keep in mind
higher airspeed, more fuel burn per hour. The second option would be to
descend to a warmer airmass. Now the manual recommends
3,000 to 5,000 feet below the optimum altitude
optimum altitude the best aircraft cruise altitude for a given weight and
corresponding air temperature. Again as flight tests have shown
descending 4,000 feet in standard conditions
corresponds to 8 degrees in total air temperature
difference but again, lower level, higher fuel burn
The third option would be to divert to a warmer air mass now
for instance
If you were to be flying close to a jet stream it
often depends if you are on the warm or cold side of the jet stream and
secondly
the closer you are to the core, the colder it can be depending where the jet stream is coming from and moving to
Now, let's say you took all preventive measures from fuel waxing up
But there is still one more chance of the fuel to freeze up
Jet fuel itself isn't entirely all fuel
there are tiny parts of water in kerosene and
Water, as we all know, freezes at temperatures below zero degrees
so in order to not clog your fuel lines towards the engine combustion chamber airplane engineers have come up with a
very clever win-win solution
They have put a so-called fuel to oil heat exchanger in place
The engine oil of jet turbines gets pretty hot and as discussed, fuel gets pretty cold
So why not let the hot oil run through a set of pipes which are adjacent to cold fuel lines?
so the oil temperature
decreases while the fuel temperature rises
If that ain't clever, I don't know what is.
Side note very often
the engineer's place warmer hydraulic lines and bleed air pipes
along the fuel tanks to radiate their heat
and warm the fuel. Also an option is to pump the fuel into the center tanks as the fuselage very often is
warmer than the wings as it is less exposed to the cold air flow. A sad side note
the mentioned fuel to oil heat exchanger was the cause for the unfortunate landing of British Airways flight 38
at Heathrow in January 2008.
Now the route from Beijing towards Europe took the plane through air masses as cold as minus
74 degrees
leading to a lot of ice buildup in the fuel lines. Now as the plane started its descent only
little thrust was used but upon final approach the pilots added power
as usual which suddenly released the ice in the fuel lines
blocking the fuel to oil heat exchanger inlet.
The blockage caused an immediate thrust loss on both engines and at 500 feet the plane
glided towards the runway.
Lacking in power, it landed short of the runway and ripped off the landing gear.
Luckily all
152 passengers and crew survived.
Following that accident, the fuel to oil heat exchanger had to be redesigned that it could cope with large chunks of ice at its inlet
I think the message of today's video is never take anything for granted on an airplane,
know what you're doing, know your systems, and stay alert.
That's it for today. Thank you very much for your time
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See ya next week. Wishing you all the best, your Captain Joe.