Last month I wrote about quality assurance issues with 100LL (How can I ensure an FBO’s fuel is not contaminated?). This month, let’s look at jet fuel.
Jet fuels fall under the classification of hydrocarbon distillates as they are basically straight run fuels right off the distillation column, with only minor trimming like hydro treating to remove sulfur.
In the US, we have commercial fuels Jet A and Jet A-1 that meet the ASTM D1655 spec. The difference between the two fuels is that Jet A has a -40°C freezing point and Jet A-1 has a -47°C freezing point.
Speaking of freezing points, in the past there was a Jet B fuel that corresponds to the military JP-4 fuel with a much lower freezing point, but these fuels have been discontinued for safety reasons.
The problem is that when refueling with Jet A or any distillate, the air/fuel ratio at the fuel neck is too lean to burn if a spark should occur. With avgas or auto gas, the air/fuel mixture at the fuel neck is too rich to burn. Jet B and JP-4 are a blend of Jet A and a light gasoline component, which means the air/fuel ratio at the fuel neck during refueling is right in the combustion range.
The other two common jet fuels are JP-5 and JP-8. These fuels are similar to Jet A except they contain some additives specified by the military. The difference between these two fuels is that JP-5 has a higher flash point specification for use on aircraft carriers.
The main quality concern for jet fuel is water, just like with avgas. But there are some additional concerns.
Most jet fuels are carried by common carrier pipelines, so the chance of getting contaminated by some surfactant or other contaminate are much greater.
The main concern with surface active material is that they can disarm a filter separator element or fuel level system. To guard against this problem most jet fuel terminals or systems have a clay filter or tower. These systems absorb any surfactants before the filter separator so that water can safely be removed.
Most commercial flight operations use their aircraft daily so there is always fresh fuel going into the aircraft. And most airlines have personnel that are trained to properly maintain their fuel farm. The same is true of the military, so we usually do not see too many problems here.
The problem with some of the FBOs and private jet fuel operations is inactivity.
Many business or private jet operators have planes that may sit for extended periods of time. As we have learned from low usage piston engines, inactivity is very hard on mechanical systems. The same is true of fuel systems.
Any aircraft or fuel system that sees limited usage is open to problems. Water can accumulate in the dispensing system or even in the tanks of the aircraft from rain or condensation. This can lead to an accumulation of very low levels of surfactants or to microbial growth. These can accumulate and even destroy a fuel tank in an aircraft, which would be very expensive to replace.
So what can you do?
It is very important for both the FBO and the plane owner to follow the proper maintenance schedule for the fuel system and aircraft. This includes proper sumping of all tanks and filters on a regular basis.
In addition, if you have a low usage aircraft, you need to look into using an additive like Prist, which is a fuel system icing inhibitor, or Biobor JF, which is a fuel system biocide and lubricity additive.
In the past some fuel suppliers would automatically add Prist to their deliveries, so always check with your fuel supplier.
In addition, aircraft owners may wish to use Biobor detection kits called HumBug bug test kits.
Another point is pilots who fly older ex-military jet aircraft on commercial Jet A may want to look into using the Biobor additive or equivalent for the lubricity properties.
