Part of the concern over the use of auto gas in aircraft is procedures used to handle the fuel.
Part of the concern over the use of auto gas in aircraft is procedures used to handle the fuel.
When a pilot uses avgas, he just pulls up to the fuel island and fills up or has the fuel truck pull up to his plane and pump in the needed quantity of fuel. Many airports do not have a dedicated fuel supply for auto gas, so pilots must find a way to transfer the fuel from a service station to their planes.
When transferring fuel, there are a lot of little problems, but the two main concerns are contaminates and static electricity.
The control of solid contaminates is ensuring that you use good housekeeping practices. This includes using clean containers and a screened funnel. I would recommend that you use a water-separating funnel and watch as the fuel is poured to look for any major discoloration, sediment or water.
Aviation fuel handling systems are designed with floating suction. This means that the intake of the fuel transfer pump is always floating on top of the fuel tank where it will pull in clean, dry fuel. Water and most solid contaminates are denser than the fuel, so they settle to the bottom and can be removed through the water drain. In contrast, the fuel intakes on service station pumps are fixed. This is not normally a problem since the throughput of most service stations is very high compared to that of most local FBOs. The biggest problem is that when a service station tank is refilled, the incoming fuel stirs up all of the contaminants on the bottom of the tank and it takes time for them to settle back down. Therefore, it is important to not buy fuel from a service station that just had its tanks refilled.
The other concern about fuel transfer is static electricity. Whenever fuel is transferred from one container to another, the fuel acts like a generator and builds up a charge. This means that one container will have a higher potential charge than the other. This is why we use a ground cable on the refueling truck. The cable bleeds off the charge build up so that there is no arcing between the fuel nozzle and the aircraft. At a service station, the hose and nozzle are electrically conductive so that the hose will bleed off the charge build up. A problem can occur if you pour auto gas from a container into your plane. Transferring just five gallons of fuel can build up a charge high enough to arc almost a half an inch, if the conditions are right. This could easily ignite the fuel vapor coming out of the tank and cause a fire. The same is true if one is pumping fuel from a tank or drum in a car or pick-up truck to the aircraft. As both vehicles are insulated from the ground, a potential charge can build up, which can arc and cause a fire.
If you have ever walked across a carpeted floor in the winter and gotten a shock when you touched a door handle, you can understand what a shocking experience that can be and why you do not want that to happen around gasoline.
Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at [email protected].
