Jet A Fuel?

Question

What is the difference between Jet-A Fuel and Jet-A-Prist fuel?

Answer 1

prist is an additive mainly for anti-icing that

lowers the freezing point of water to -43 degrees centigrade

Answer 2

Water molecules are entrained in Jet A with the highest acceptable rating being 30ppm per ATA103.

Adiabatic lapse, (the decrease in temperature as altitude increases,) can cause the water entrained in even acceptable fuel to crystalize out of the fuel and clog fuel filters. Obviously, an engine being fed fuel from a blocked filter doesn't run.

Three ways of treating that are fuel heating methods, which typically exchange the excess heat of the engines to melt ice crystals before they get to the filters, older Hawkers used methanol injection to dissolve the ice accumulations when a warning light announced a problem, and common to really old jets such as the 20 series and 35 series Lear was the addition of Prist. Or Fizzy (Generic name,) as the fuel is being pumped into the tanks.

The additive works much like the anti-freeze in your car's radiator. It moleculary bonds to the entrained water and prevents it from freezing. Unlike the anti-freeze in your radiator, Prist and Fizzy are both flammable.

There are three methods of delivering Prist to the fuel in an aircrafts fuel tanks; spray can, truck injection, and ordering pre-blended fuel. Depending on which FBO you use, should you need it, you might recieve it in any of the delivery methods listed above, or even get if it you don't need it. (Won't hurt anything.)

The problems with Prist, and preblended fuels, is that as oil floats on water, if you have free water in a tank, the prist blends with it and dead bacteria to create "apple jelly." (No, I didn't make it up.) This is part of the reason that many jet aircraft periodically require a "tank & plank" inspection.

The other part of this question is that jets usually don't glide well. Off field landings in jets usually don't come out well.

From a customer service standpoint, if the pilot calling in doesn't specify, ask. If the line service tech calls back and can't remember if the aircraft requires it or not, (or read the placcard beside the fueling point,) give them prist whether they want it or not.

Most pilots flying aircraft that need prist will more than gladly tell whomever answers the phone at the FBO that they need it. In the event that the person answering doesn't know, didn't remember, or didn't make a note, I'd rather give them the prist than risk killing someone because I didn't.

At only 10-15ppm, for prist, (or fizzy,) giving it away is less expensive than trusting my entire crew to have everything together when someone calls at 3:30 in the morning.

JT

Answer 3

I'll concur with the detailed answers.  Here's the quick and dirty summary.

Prist is an anti-icing additive added to jet fuel.  It also has anti-microbial properties.  Some airplanes REQUIRE it.  Other airplanes don't require it because they have an anti-microbial lining in the fuel tanks and the engines have fuel heaters as a precaution to melt ice so it doesn't clog filters/lines/nozzles.

If Prist is required per the aircraft manufacturer, USE IT.  If it is not required, Jet A with or without Prist are both acceptable.