Lately, I have received a number of questions concerning grounding or bonding an aircraft during the refueling process.
The reason for using a bonding strap during refueling is that when an electrically, non-conductive fluid like Jet A or 100LL is transferred, these liquids build up static electricity that can arc and cause a fire if not dissipated.
This is like how your body can build up static electricity when you walk across a carpeted floor and then arc when you touch a grounded item.
In the past, we called it grounding and we connected a jumper cable from a ground post to the plane and to the refueler.
But the airlines found that having a ground cable connected to a large airplane in a storm can lead to “electrical” and other problems.
So now the standards call for only one cable connecting the plane to the refueling vehicle. This ensures that the plane and the refueler are at the same electrical potential when the hose is placed in the filler neck and during the refueling process. This is called bonding, as opposed to the old grounding.
One of the problems with this process is that most refuelers use a cable retracting reel for the cable. The contacts in the reel can become corroded and not have electrical conductivity. That’s why they need to be checked with an ohmmeter every month.
Another problem is where to connect a bonding cable on your aircraft.
Some say to connect it to the exhaust stack. This may be OK, but some owners do not like their chrome stacks all scratched up.
Others say to bond to the landing gear or front strut.
The problem is that a bonding location should be identified on all new aircraft. But none of the manufacturers are willing to do that.
What I suggest is that, if you own an aircraft, go out with an ohmmeter and check to ensure that a chosen location on the plane does have electrical conductivity to your fuel filler neck. (Do not check conductivity with an open filler cap.)
Now you need to identify your chosen point with a label that is visible for the average FBO employee. This process is especially important for composite aircraft.
Another question concerns plastic fuel cans and how to ground them. There is no great answer here.
If you pour fuel from a metal container into an aircraft, the static charge can build up in the fuel and get transferred to the metal container. This charge can then jump a gap between the can and the plane and cause a fire. The transfer of just five gallons of fuel can build up a charge great enough to jump over half an inch under many conditions.
But with a plastic container, the static charge cannot build up on the container wall, so there may not be a problem as the charge will dissipate once in the tank.
However, if you are using a metal funnel, then you should bond the funnel to the plane.
In the past, I have read articles that recommended placing a metal strip into the plastic can before pouring and bond this to the plane.
I am not sure this is necessary and am looking for examples of static electricity accidents with plastic containers. I have not found any problems, but will continue to look. If any of our readers know of any problems, please let me know.
Fueling safely from portabe can should only use DOT or OSHA approved container. A Google search one can find stories and pictures of plastic gas containers burning and exploding. The FAA publishes training advisories on bonding and fueling aircraft. FAA does not allow grounding while fueling. I have over 65 years working aircraft line maintenance and full agree with the FAA on this issue.
The warning one get on a static discharge is after the occurance when it may be too late.
Clothing should be considered as it could be part of the static build up.
Dear Mr Jermakian,
I want to support your group of volunteers working with old planes in Floyd Bennett Field
I have read an article by Mr Luke Spencer where you mention you need to buy fuel
I wonder whether if you can get in touch with me to discuss your needs
thank you very much
best regards,
Arthur Papikyan
646-280-8411
Hello guys I work in the oilfield and safety people say no to plastic because plastic will make static elec they require metel buckets only to stop static elec so I guess we all have a fuel vapor problem of all kinds so a good ground is good in most problems is all I can say n thanks I got my two cents in I hope it helps im an oilfield worker in texas .
It seems there are three sources of ignition during refueling: The fuel, the airframe and the refueler.
Gas cans. The usfs has this handout that pretty much covers the waterfront: http://www.fs.fed.us/t-d/pubs/pdfpubs/pdf95512323.pdf Of interest here and on the OSHA site is flashback supressors in the gas can and receiving vehicle. It can be nothing more than metal window screen poked into the inlet and spout. Many mistake it for a filter.
F16 and 18 are essentially plastic planes. One wonders what precautions they take for refueling on a carrier deck or inflight refueling.
Some heli-loggers claim that the cable arrives with a heck of a charge and has to touch ground before the logger can hook it to the cable bridle. If that condition is true in fixed wing, and it retains that charge taxiing to refueling, then grounding seems like a good idea prior to touching a fuel nozzle to it. Bonding the plane and fuel source together further completes the circuit. I like the idea of a ground clamp at the nozzle that the fueler attached to the plane prior to touching the nozzle to the plane.
Scan the web for ‘refueling fires’ and there are multiple videos of ladies who sit in the car while refueling, jump out and touch the area where fumes are boiling out of the tank, get a spark and fire ensues. https://www.youtube.com/watch?v=WohRAM4_NQg How well the fire develops depends on what they do next. Gas tanks with flaps and the fuel shutoff are excellent flashback suppressors. People who freak out and spray fuel all over have a different outcome.
This points to three things: First: Ignition came from the person, not the vehicle or cell phones. Sliding across synthetic seats in synthetic clothing is the setup. Second: Old people grab ahold of the vehicle in various ways to support themselves and bond with the vehicle before touching the nozzle. Young people don’t and have fires. Third: Where is the fire extinguisher?
Does the common ground (steel or al) at most avfuel(100LL) pumps need to be covered w plastic tube? Or is the bare cable ok?
Plastic covering only protects the cable from abrasion, corrosion, stray wires, etc. Not necessary but helpful
I have a piper cub with wing tanks. I fill it from 5 gal cans, always plastic. I’ve been told that the plastic “gas” cans have some additive in the plastic to dissipate the static but have no way of knowing for sure. I always try to keep the flexible nozzle of the can in contact with the filler opening. I’ve never seen any sign of a spark doing this but i only put in 5 gallons at a time and seldom more than 10 in total so maybe I’m not in a position of risk with what i do.
One thing, I have heard of a fire starting at the tank filler from a spark, never seen it but heard of it, so I keep a big cloth right at the filler point when I’m filling and work on the assumption that maybe, with luck, if a fire started I could just ram the cloth into and over the filler and smother it before it got going? Probably wishful thinking but when you are standing on a ladder balanced on a float… well wishful is about all you’ve got!
After loosing an airplane to a static electricity fire and sending a year rebuilding it when it was one year out of a fresh rebuild I had adequate time to think about and research the issue.
The problem is that the fuel in the plane and the plane, assuming a metal tank, will be the same charge but the fuel in the can may be a different charge. If the can is metal then the fuel and can are the same charge. If you touch the closed can to the metal plane the charge will dissipate. If there is no difference in charge, there is no chance of a spark jumping from one to the other. The difference in charge if there is one is called potential difference or voltage.
Plastic is usually an insulator. Mr funnel (the only funnel I would use at this point) is conductive to a limited degree. However when checking resistance there is some. Mr funnel will stop water, always a potential issue when fueling from cans.
If a plastic can is used it will allow the fuel to remain at a different charge than the plane and when the fuel is poured as it gets closer to the differently charged plane and its fuel the spark can jump from one to the other in the presence of fuel vapor.
I put a bolt through the plastic can or the filler spout of the plastic can with a standard ground strap on the inside where it is in contact with the fuel. I connect a wire to the bolt when the plastic can is closed, no vapors are present and the can is not under the plane. I then take the wire to the plane and touch to to metal and any potential difference is dissipated prior to the can or tank being open. No difference in charge and therefore no spark.
Static electricity is higher risk in cold and dry climates. Wearing wool or poly pro pollens also makes it worse.
My caps and receptacles are isolated in composite wings. What should I ground to? Always get a chuckle out of my friends clamping their exhaust….
Jeff: Static electricity will equalize between the two through the bonding strap rather than the fuel hose. The issue is when the plane and the truck have different electrical charges (i.e. one is negatively charged and the other is positively charged). If not bonded, and a sufficient differential builds between the two, it will bridge through the fuel hose and the aircraft. Bonding just provides a path of least resistance to travel.
Miami Mike: In short, it has to do with how automobiles deal with the gas vapors. As you fill an airplane, the vapors in the tank push up and out the filler nozzle. The vapors are what will catch fire with a spark. Modern cars push them through a filter canister to be later drawn into the engine intake, which is why you really don’t smell much gas at the pump anymore. I believe there is also an internal bonding mechanism within the nozzle, but I’m not positive. I know there are hoses with internal bonding wires embedded in, but if I recall correctly, they tend to break from frequently being wound around spools like they are on aircraft refuelers.
Years ago I was working as a gas-jockey for a community college fight school. The CFIs were always in a hurry and did not believe in grounding the airplanes as “they were too slow to build a static charge.” We grounded them anyway, Piper Cherokee Warriors and Arrows. I had a visible spark only once, with the Piper L-21 Super Cub that was used for spin training.With the ground clip about an inch from the exhaust,(I had just started to squeeze the clip), a bright blue spark jumped the gap! This was a sunny day and the spark was fully visible. This was the slowest plane in the fleet, I don’t remember if it was really low humidity or not, but I doubt it being a Michigan summer. The Razor Back,(fiberglass), fabric may have contributed to the static charge build up as well.
Interesting article. In boats the filler neck and tank used to be bonded, but it is no longer required. Nor is the boat ever grounded or bonded to the fueling equipment, unless it is in the water.
Also in the article it states to bond between the fueling vehicle and the aircraft but not grounded. How is the static charge discharged?
Portable tanks are to be put on the ground when filling at a gas station to prevent static charge build up in a truck bed. But no discharge when fueling or when in the truck?
Jeff, are you sure? The fuel entry line is a standard fuel hose with a built in ground which is grounded to your ‘aluminum’ fuel tank when steel fuel nozzle enters the ‘metal’ entry, which is in contact with the engine grounding system. You will see a ground connection on the tank which is a common for the fuel gauge as well. This same system can be used in composite aircraft with a ground attached to the entry which connects to the aircraft ‘ground .
Question: Why don’t we need to ground cars, trucks and motorcycles when we fuel them? Essentially the same fuels, essentially the same machinery, all insulated from the ground by rubber tires. Hundreds of millions of road vehicles are refueled worldwide every day, in every kind of weather (hot, cold, damp, dry, windy, calm) yet they don’t explode and it is safe to say NONE of them are grounded, and sometimes they are refueled by people (morons) with lit cigarettes in their mouths!
I intend to ground my airplane every time I refuel it, but I’d like to know why airplanes are so different from other vehicles (other than they fly and are much more fun). Is this a function of putting 30,000 gallons of fuel into a jet versus two gallons of fuel into a mower? Is this something left over from WW2 technology (and if so, what)? I’ve also heard that de-fueling an airplane is more dangerous than re-fueling one, also for static electricity reasons.
I’m an AGI, and I’m curious about stuff like this . . .
one factor to be considered is the flow rate and the rate of static build up on a conventional car you may only be pumping at about 40 litres per min whereas on a 747-400 i have uplifted 140 000 liters in 36 min which is 3888.88888889 liters per min most refueling truck driver make it standarf practice to first job the bonding on arrival at the aircraft but as pilot oe engineer it is our duty to check before a figure is handed over or valves opened and commencing of the delivery begins . practises vary worldwide so always check
my composite aircraft has a conductive webbing between layers of the composite. I am told it is for lightning strikes, but don’t know anymore than that about it yet. I found this out when having a wing ding repaired recently.
Yes that metal mesh is for lightning strikes. Composite airframes tend to explode when struck so they need that protection built in if they are intended for any serious IFR use. Of course it could help with the static discharge being discussed here as well, I don’t ever recall that facet being among the selling points.
Tires have a compound that provides a ground. When you slide out of your car, the cloths you wear can generate static electricity and because you are separated from the metal in your vehicle you will carry the static till it finds a place to dissipate. Grab some bare metal or chromed metal as you leave to dissipate the static electricity. As I said in a previous post, when you see the spark, it may be too late.
That is all fine for the classic metal airframe but what does one do with a composite airframe? As I recall fiberglass makes a great insulator so just how does one ground a non-conductive airframe effectively.