Originally posted by elpasys
"Filtering or rapidly pumping a liquid that is a relatively poor electrical conductor, like jet fuel, can result in a static charge being created
much faster than it dissipates." [i.e. entropy growth]
"When the accumulated charge exceeds the ionization potential" {i.e. maximum entropy state]
"of the air above the liquid, it can discharge from the liquid surface as a spark. The energy of the spark can initiate an explosion if the liquid is
flammable and the composition."
More:
Chevron
Aviation fuels
2. Aviation Turbine Fuel Performance
You missed this bit from your same link
To prevent explosions triggered by a static discharge, well designed fuel handling systems use bonding and grounding (or earthing), pumping rate
limits, and time for charge dissipation (relaxation time), before the fuel is exposed to air.6 Military jet fuels and international Jet A-1 require
the use of an additive to increase the electrical conductivity of the fuel. Conductivity improving additives are also called anti-static additives
or static dissipator additives. Use of the additive reduces the hazard of charge accumulation for handling situations that are less than optimum.
The additive does not prevent charge generation, rather it increases the rate of charge dissipation by increasing fuel conductivity.
And yes you have to ground an aircraft while you fuel it, to dissipate all static build up. Though honestly chances of static from pumping are just
about zero (maybe its higher in dry climates), they control the speed that you pump at and the pressure, it’s all governed by the hydrant truck.
Jet-A is really not that different then diesel fuel used in trucks, and we used to fuel our diesel ground service equipment and run it off of Jet-A
Its funny I was an aviation fueler here in Florida and I have never heard of Entropy, Delays for Fuel stabilization (plenty of fuel delays though,
LOL. Means that there are too many planes and not enough fuelers), or fuel weathering (unless you mean the density change associated with temperature
meaning that the fueler was unable to deliver the poundage of fuel requested). Now it could be that these factors are a bigger concern in area’s
where it’s drier and more prone to static discharge, but you think that I would have at least come across these terms before.
Then there are the wing vents that open to the outside atmosphere, and there are only two, not one per tank. To my knowledge they cannot be closed,
and if the center is overfilled it spills over to the wings, and if the wings are overfilled the fuel spills out onto the ramp out these vents. I have
even seen aircraft go out that are so full that the fuel is splashing out of the wing as the wings bounce with each bump on the taxiway that the plane
hits.
The Volumetric Shut off it seems to me (would have to get out my old books and dust up a bit) was nothing more then an arrow on the gauge that could
be set to the pounds per tank to automate shutting the tank valves. These are only available on the newer aircraft and like any other fancy
unnecessary item would break all the time, and you were better off to fuel manually and never even bother with them to begin with (push the arrow to
the top of the gauge). I mean how hard is it to watch the tank levels and snap down a button when the arrow hits 9K on each wing tank and 5K in the
center anyway, by way of example?
I think that zaphods busted wing picture was a stuck fuel valve, where the fuel is trying to pump into a valve that is stuck shut until the pressure
builds so high in the pipe that it structurally damaged the plane, but correct me if I am wrong there zaphod.
It also sounds like you feel that there are more tanks on some of these aircraft then there are, as an example there are 3 on a 737, unless it has an
aux tank, not multiple ones in each wing. If the wing tanks are in fact actuality broken into multiple tanks per wing then there is no way for the
fueler to control them, they simply flow one into the next, or the fuel is transferred by pumps that are not under the fueler’s control. But I can
assure you there are three gauges and three shut offs on a 737.
So no offence but this does not sound like a serious concern to me. Besides if this was such a danger there would be aircraft popping at the gate
while being fueled all the time, and I cannot say that I have ever heard of this happening once.
Originally posted by elpasys
Please read between the lines of the official report:
"The VSO (volumetric shutoff) will also shut the valves when fuel enters the tanks if a fuel tank is overfilled. While the accident airplane was
being fueled at JFK the fuel system's automatic VSO activated"
[due to fuel weathering (nucleate boiling)] (the unspoken words)
"before the fuel tanks were full. A mechanic overode the safety system and finished fueling manually."
"TWA Flight 800 was schedulded to depart JFK (New York, New York, USA) for Charles de Gaulle Airport (CDG, Paris, France) about 19:00; however, the
flight was delayed"
[1.2 hour] [due to fuel weathering (nucleate boiling)]. [Official:] (the unspoken words)
"a disabled piece of ground equipment (a fleet service vehicle was blocking the accident airplane at the gate) and concerns about a suspected
passenger/baggage mismatch (the missing passenger was on board the whole time)."
To me this means that the crew wanted say, 10K of gas, but because of the density of the gas being higher then normal due to temperature, they could
only fit 9K and had to force the poundage on the plane by fueling manually since the gauges want to shut off when it hits that arrow. The part of this
that makes no since to me is that you seem to assume that you can squeeze 10 pounds of crap into a 5 pound bucket and I am sorry to report that if you
try with on a commercial airliner, your going to be on the phone with the fire department explaining why you have a fuel spill at your gate. Now I am
not a mechanic and perhaps there is some way to make this happen, but I have never heard of it.
So yeah it’s a fuel delay in that they could not get the fuel load onto the plane that the flight crew requested, or a gauge was sticking and would
not let them top off the tank. To be honest a 1.2 hour delay sounds a lot more like a fueler over-fueled a tank and it had to be de-fueled, which is a
pretty slow process since the plane does not have the large pumps that the truck does to suck the fuel back out of the tanks. The only other thing
that takes that long is to transfer fuel from the center to the wings.
As to the rest, that is SH that happens at an airport, nothing unusual there, equipment breaks down in the pushback path of the aircraft, and the
baggage/passenger list has to match up, stuff like that.
I also want to put in here that the reason that a plane officially takes a delay and the real reason are not always exactly the same. It used to be a
trick, if the deck crew allowed you to do it, that to get around a delay, you could push back the plane a few feet to finish loading bags or whatever
you had to finish, and it would get charged as a taxi delay and does not get counted against the airlines on-time records, as an example.
[edit on 10/22/2005 by defcon5]
