Grounded: What’s the proper way to ground during refueling?

Why is it important to ground an aircraft during refueling? What’s the proper way to ground an aircraft during refueling? These are just some of the many questions I’ve received about the process, so I thought I’d tackle them in this post.

We ground an aircraft during the refueling process to ensure that the plane and the refueling apparatus are at the same electrical potential and to dissipate the electrical charge that is generated by the fuel transfer process.

It is very important to remember that whenever fuel is transferred it acts like an “”in-line”” generator to build up an electrical charge. In an auto service station, the conductive hose is used to dissipate the electrical charge buildup. In addition, autogas has a higher vapor pressure so that the air/fuel ratio at the fill neck/fill hose contact point is too rich to burn.

In aviation, we have the added safety of a ground cable. At a ground mounted avgas pump, the ground cable goes from a ground strap to the aircraft to dissipate the electrical charge. In a refueling vehicle, the cable goes from the refueler to the aircraft to ensure that the two vehicles are at the same electrical potential. The problem here is if someone is standing on the ground and reaches for the nozzle, that person can be a ground path causing arcing. That is why on large aircraft a refuel vehicle will usually have ground cables connected to the aircraft and to a ground strap.

The important thing for pilots to know is the location of the ground lug or connection point for your aircraft. It is important that the lug has an electrically conductive path to the fuel filler neck or port. If the lug gets painted or is rusty, you will not have a good conductive path to dissipate the charge buildup. I would recommend that every aircraft be inspected as to the condition of the lug and, on a periodic basis, use an ohmmeter to check the conductivity between the lug and the fuel tank neck. I use a long jumper wire to help check conductivity. If you are using a metal can to transfer fuel, always use a cable to connect the can to the aircraft. If you are using a plastic fuel container, place a long clean metal strip into the container and then connect a jumper from the strip to the aircraft.

The important points for FBO personnel to remember are that the ground cable system must be checked periodically and used for every refueling operation. The periodic checks should be performed at least every month and should include a visual inspection of the ground cable, clamps and reels and a continuity check with an ohmmeter. Two of the most common problems are corrosion of connections and poor contact in the cable reel. So connect an ohmmeter to the cable end and ground strap and then pull the cable out of the reel to ensure continued conductivity. It is also important for FBO personnel to learn the proper ground point for each aircraft and to use ground cables when defueling aircraft as well.

Always remember that electricity has its place in this world, but one place that it shouldn’t be is near the fuel filler neck.