This question may seem a bit silly, but it crossed my mind yeaterday.How do pilots check fuel quality in the airline world, in terms of water in the fuel etc? Also...do airlines follow the GA practice of fillig the tanks overnight to prevent condensation?thanks in advance

Um, i know in the GA world the fuel testers will show water right away when u drain them from the sumps. (You can visibly see the water when it is present) Idk if airlines drain the fuel like GA. I also think that Jet A (Jet fuel) is a puerified form of kerosene so I'm not sure if there are diff. properties associated with it.

Each tank has one or more "drip-sticks" under the wings, or in the case of the centre tank, under the body.It is usually the responsibility of the ground engineer to pull the sticks to drain any water in the bottom of the tanks (fuel floats on water, obviously) and to sign off that it has been done. Some airlines require the captain to either perform the check himself, or to witness it being done.Steve

Steve-Actually the dripsticks/floatsticks are for determining fuel quantity in the tanks..never heard of them being used to drain off water (would be quite messy and tick-off theenvironmental police) and the tubes would have to be at the tank low-points.The fuel (Jet A) has a anti-ice/biocide added to it (used to be called "Prist") to prevent water freezing. If the fuel strainer gets "plugged" the fuel-filter-by-pass light comes on and the fuel heat switches are thrown...this is enough to melt the ice on the strainer.In the old 727 the Flight Engineer would manually throw the fuel heat switches when the by-pass light came on...on the 75 and I think 76 its automated.Never ran across a problem with water in the fuel, but I'll do some checking and see...Tim__757

It's guys like me that check for water in the fuel. Part of the daily check that the maintenance engineers have to do is drain water from the fuel tank. A tool is inserted into the fuel drains and a sample is taken. As long as water is present (quite easy to spot as it is denser than the fuel and thus is visible at the bottom of the sample bottle) samples are taken and dispensed off in appropriate containers. Once no more water appears in the sample the tank is then said to be relatively free of water. The bottle that we use is about 1 litre in capacity, and I have never had to take more than six samples before no more water shows.pAnMaN

PanManBetter you than me...hated smelling like jetfuel all day....Tim--757

hey Tim,Who do you fly for?

I tend to shy away from giving all that information out-made the mistake before on another forum and had to change my email addy etc etc.I just lurk...but if you are airline savy and read when I answer you'll know.Tim__757

CheckAirman and All,Ran this by a friend. Apparently, water is not an issue for turbojets as a water fuel mix will actually produce a higher thrust from a turbine powered engine. Such was the case with "water wagon," 707s that actually had water tanks for a water injection system. Also, water injection systems have even been used on turboprops as was the case with the BAe 3100.My friend went on that he had never heard of major or regional pilots flying turbine powered airplanes having to check for water in the tanks. Maybe this is due to additives in the jet fuel so what small amounts of molecules left would have no effect other than to boost output.Anyone else?

I think you'll find that water injection is not achieved by adding water to the fuel, but by generating a mist of water in the intake or compressor of the engine (helping condense the air for better combustion in the core of the engine).AFAIK, all jets are checked for water in the tanks on a regular basis. On the larger jets, this will of course not be the responsibilty of the pilots, but of the engineers.Engines, however, will tolerate small quantities of water in the fuel. Fuel provided to aircraft invariably contains water in suspended form... but the water has a tendency over time to sink towards the bottom of the tank. Small hydromechanical scavenge pumps (with no moving parts) in Boeing aircraft like the 767 and 747 suck up small quantities of water found in the bottom of fuel tanks and this is mixed with the much larger main fuel flow going to the engines. These hydromechanical pumps allow the water to be removed over the course of the flight: The last thing a pilot needs is finding him/herself short of fuel on a flight... and then finding nothing but water at the bottom of the tanks.Hope this helps.Cheers.Ian.

Ian,I agree 100%. Injection systems seem to be geared for the intake. But my friend also gave the example of a straight pipe flying through a rainshower without injection. His point was that if there were small amounts of water in the fuel it would make no difference for a turbine engine. The turbine will keep burning. . .until either the ignition is overwhelmed, the O2 runs out, or the fuel stops running.Good point on modern jetliner fuel systems. Is it even possible for water to reach the engine at all?The only question I have is regarding possible additives in Jetfuel and the properties regarding this fuel? Are water molecules even allowed to bind together even in small amounts within this enviroment?

>Good point on modern jetliner fuel systems. Is it even possible for water to reach the engine at all?Perhaps I didn't explain properly....The water in the bottom of 767 tanks is slowly mixed with the main fuel flow, so unless the fuel cutoff levers are in CUTOFF, the water will inevitably get to the engine. Water is assumed to be in the fuel and fuel systems are designed to accommodate this water. For example, on the early series JT9D engines (fitted to 767's), an automatically (with manual backup) activated fuel heating system was designed to look at fuel differential pressure across ice-susceptible fuel system components such as fuel filters. When the pressure gets too high, the heat is turned on. i.e. high differential pressures are assumed to be blockages due to ice. Even if the filter was blocked because of other reasons, the heat would be turned on!>The only question I have is regarding possible additives in Jetfuel and the properties regarding this fuel? Are water molecules even allowed to bind together even in small amounts within this enviroment?I'll have to hand you over to the fuel specialists here.... This is not my field of expertise (if I have any at all) ;-)Cheers.Ian.

Where I work, the fuel bowsers have a guage fitted that is similar to the Fuel Test Kit you can buy for a small GA plane. Instead of dipping the tanks to check for water, the engineers usually have a quick look at this guage to check for any water contamination in the fuel before loading.

In the "Oh yea, I remember that now..." Department.The one fun thing that happens infrequently is a fuel probe will get a little slug of water in it...owing to the different density and electrical ability this will blank out the fuel quantity till it clears.Just another day at the office....Tim__757