When I was young, I enjoyed watching Bugs Bunny and, on occasion, Bugs matched wits with Marvin the Martian … who was usually working on blowing up the Earth. Bugs managed to foil Marvin, who had the usual line of the foiled nemesis: “Where’s the big Kaboom?”
Much like Bugs, our job as pilots covers some of the same ground — how to keep the fueling of our plane from turning into the “Big KaBoom.” In case you didn’t know it, fueling your airplane can be very dangerous, if you don’t know what to look for.
CASE IN POINT – My airport has suffered for years with an “antique” fuel truck. Don’t get me wrong, I like antiques — well kept antique airplanes fly for years and years without a problem. The key was “well kept,” because this fuel truck was ANYTHING but. Starting it was a challenge, and once started, it lumbered across the ramp like an arthritic elephant headed to the water hole. Actually, saying that is an insult to arthritic elephants in a way, since I’m told they move a lot more quietly than this truck did.
Needless to say, when the airport bought a “new, used” fuel truck, we were overjoyed. Gone was the old, corroded carbon steel tank, replaced with a corrosion proof aluminum tank. The trucks were fairly recent, which meant you could still get parts for them at the local auto store. Better yet, the truck engine was recently overhauled, and didn’t die when you engaged the fuel pump PTO.
SOUNDS PRETTY GOOD, RIGHT? Well, pretty good is just that, because something was missing from our fancy new fuel truck. What was missing was the most critical part of the truck, because it is the part that makes sure the stray electric current has a path to ground. In case you haven’t guessed it, I’m talking about the ground strap.
HERE’S HOW IT WORKS – As the line person adds fuel to your airplane, the flow of fuel through the rubber hose creates static electricity. The fuel flowing into your fuel tank does the same thing – it passes its static charge to the airframe. This is why the first thing your line person does before they fuel your plane is to connect up the ground wire between your plane and the fuel truck. This assures that the static charge remains at the same potential between the truck and the plane. If there is no difference in potential, there is no chance of a fuel vapor igniting spark occurring.
STILL, WITHOUT THE GROUND STRAP TO SIPHON THIS CHARGE OFF TO GROUND, THE STATIC CHARGE STAYS WITH THE FUEL TRUCK. The setup on this one is insidious, because you can’t see it, but when it happens, it’s hard to miss the aftermath.
THE FUEL TRUCK, MISSING ITS GROUND STRAP, trundles out to your plane. The line person dutifully connects up the ground wire to your plane. LITTLE DOES HE KNOW THAT THE GROUND WIRE BROKE ON THE LAST PLANE, AND HIS CONNECTION DOES NOTHING TO PROTECT HIM. He engages the PTO, and pulls the fuel hose from the truck and over to your fuel tanks. After opening the cap, he carefully inserts the nozzle into the fuel tank.
YOU JUST GOT BACK FROM A LONG FLIGHT. Your fuel tank has a little avgas inside, and a lot of vapor. As the fuel nozzle is inserted into your fuel tank, a HUGE EXPLOSION OCCURS, KNOCKING THE LINE PERSON BACK FROM THE FUEL TANK OPENING AND ON TO THE GROUND. The ensuing fire quickly spreads, destroying your airplane before the airport fire department can arrive.
YOUR PLANE JUST GOT SHOCKED – THAT’S RIGHT – SHOCKED BY THE FUEL TRUCK. Since the fuel truck wasn’t grounded, it developed a pretty good potential as it traveled along the ramp. That potential was protected from ground by the rubber tires on the truck, and on your airplane. When the line person inserted the fuel nozzle into the fuel tank, he got it close enough to the tank to allow that static charge to equalize – and it did with a fairly good spark! KA BOOM!
AVOIDING THE BIG KA BOOM:
- Look over the fuel truck – make sure it has a ground strap. These straps can be anything from a black strip to a chain. Unless it touches the ground when the truck is stopped, IT ISN’T WORKING.
- ALWAYS GROUND YOUR PLANE TO THE FUEL TRUCK WHILE FUELING. While these ground straps may break, they are your only line of defense.
Nobody wants to see his or her airplane get burnt to a well-done crisp. Take a moment and become more familiar with your local fuel truck. The airplane you save from a toasty demise will be your own!