Citation 525 pilots help!

jgheggie

jgheggie

Well-Known Member
Hey guys,

I have a question for anyone flying a citation. Or other light jets I suppose....

What are the effects of NOT adding prist to the fuel?

I ask because my little cousin works at an FBO. He fueled a citation yesterday that required prist. He says he injected it and double checked.

Last night his boss called and said he must not have added prist to this aircraft because they got a "filter bypass warning light" in air.

I just want to know what kind of damage it could have done. He didn't get fired...so I assume it wasn't incredibly large of a screw up??
 
PRIST is primarily used as an anti icing agent to lower the temp at which the fuel will start to gel up. JET-A has a min temp of -40ish and PRIST will further lower that number to -50ish (I might 5 degrees off one way or the other). The smaller jets, Citation IIs, BeechJets, etc don't have true fuel/oil heat exchangers and can't keep the fuel relatively warm at altitude.

A Fuel Filter Bypass warning doesn't mean he didn't add PRIST, there is a whole list of things that could cause that. Unless the jet was nearly empty and all the fuel your cousin put in was negative PRIST I would have a hard time believing that the lack of PRIST on one tank of gas (partial tank of gas) would cause that.
 
Not to familiar with light jets, however sounds like something clogged the filter. I would guess it could be gelled fuel from not using the prist. In my short career I have only heard one story from a plane going down because they determined it was from gelled fuel from lack of prist.
 
What kind of 525? I used to fly the 525B (CJ3), and it had a fuel/oil heater. It did NOT require prist, and we always fueled negative prist.
 
A little more info...he said he pumped 177 gallons in the a/c. Not sure how much they hold. He said the boss told him the pilot determined that the lack of prist is the only cause.

In my (limited) experience, I don't see how the pilot can say that for sure.

What are some of the other things that would cause this filter bypass light? Pilot said they tested the fuel and no particles. So he doesn't think it's contamination.
 
I depends.... How much fuel was in the tank before he fueled it? There is a relative ratio that needs to be met to prevent icing. That being said I highly doubt that this would be the only cause for a bypass light to come on in flight. It is just the easiest reason to point fingers.
 
CJ2+, CJ3, CJ4 DO NOT require PRIST because of a fuel/oil heat exchanger.

Also, PRIST explicitly says on their web site that their product is no longer an official bio-boar, anti fungi additive.
 
I don't know how much fuel was in the aircraft. He said he pumped 177 gallons into it. He said the aircraft requires prist.

I'm just confused because I always though that prist was more of an option rather than required. I remember my line service days and some aircraft taking it one day when it's cold but then not taking it the next day when it's warm. So it makes sense that it lowers the freezing point.

What I don't understand is, this aircraft apparently requires prist at ALL times.

Everything I have looked up (google) says that the filter bypass warning is likely caused by debri or contaminated fuel. How can the pilot be so sure that it was due to the lack of prist?
 
PRIST used to be an actual biocide, but the newer formulation no longer qualifies, and it is no longer marketed as such. I don't have any CJ time, but in the Lears, we need PRIST. That said, unless you landed with very, very low fuel, and took a lot of fuel that was not mixed with PRIST, there'd still likely be enough remaining to give the desired effect. Remember, PRIST has a low and a high concentration at which it is effective, and most FBO's and refineries blend in the middle of this range. So, if you had, say, 100 gallons in the tanks, and you added 200 gal of PRIST- negative fuel, you'd likely still be close to the line of having enough, and there likely wouldn't be an issue.

This certainly isn't to condone operating aircraft that require anti-ice additive without it, but in reality, it only comes into play if you get multiple fuel loads without it to where there's no protection in the resulting fuel mixture.
 
Thanks guys.

He was just worried because he really believes he added prist. He's positive in fact. But he's down on himself for the potential risk. He feels bad because he thinks he could have risked lives if he did in fact forget prist.
 
jgheggie said:
Thanks guys.

He was just worried because he really believes he added prist. He's positive in fact. But he's down on himself for the potential risk. He feels bad because he thinks he could have risked lives if he did in fact forget prist.
Click to expand...

Well lets play devils advocate here for a second and say he didn't turn the prist switch on... sure he is responsible in some manner BUT ultimately the pilot should monitor fueling to ensure that he did turn the prist switch on. People are human and make mistakes... I'd say about 20% of the time when I wander out and ask about prist I get a "deer in the headlights" look. Sometimes they know and sometimes they are clueless.... then its time to stop fueling and get a someone who does know whats going on involved. Only once have I ever been completely fueled where prist wasn't added and it was due to a pump failure.
Ultimately it is up to the PIC to ensure the safe operation of the aircraft END OF STORY.
 
A lot of FBOs premix PRIST into their fuel. Perhaps he should make the suggestion. The potential of forgetting to flip a switch is greatly reduced when they do that.
 
jgheggie said:
Thanks guys.

He was just worried because he really believes he added prist. He's positive in fact. But he's down on himself for the potential risk. He feels bad because he thinks he could have risked lives if he did in fact forget prist.
Click to expand...

Tell him to think about it this way... If prist required a/c were that sensitive to one fueling with a lack of prist, testing fuel after uploading would be mandatory.
 
So he added 1000# of fuel give or take to an aircraft that can hold I think at least 5000# or more. I have the type but I forget now. So only 1/5th (or less) of the fuel? It wouldn't matter. I know for a fact I've done a leg or two with no prist when the FBO didn't have it available.

There are lots of reasons that fuel bypass light could come on. I highly doubt it had anything to do with your friend.
 
I HIGHLY doubt the lack of prist would cause a fuel filter bypass light to come on.
 
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