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airkas1
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Posts: 7904
Joined: Sat Dec 20, 2003 7:01 am

Fuel Filter Bypass Warning

Thu Mar 10, 2011 2:27 pm

Hi guys,

Today we had an aircraft, a C525, divert to the airport because it had a fuel filter bypass warning for both engines. They didn't declare an emergency, but they did say over the radio that they wanted to land as soon as possible.

None of us in the office knew what that actually meant, what kind of 'emergency' it was. So after marshalling the plane, I stayed to ask the pilots if everything was ok and what the fuel filter bypass actually does. Due to the strong winds I could barely hear it, but he did mention something about possible contamination of the fuel at the airport of departure (water in the fueltanks). They rwere on the ground for about an hour, refueled, and went on their way again without any problems.

Since I'm still a bit confused about what this fuel filter bypass system actually does, I thought I'd ask here. Does it only involve a contamination of the fuel or is there more to it? Sorry if it's been asked before, but neither a Google and the search function of this site provided me with a clear answer.

Thanks in advance!


-Kas
 
LMP737
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Joined: Wed May 08, 2002 4:06 pm

RE: Fuel Filter Bypass Warning

Thu Mar 10, 2011 3:38 pm

When fuel bypasses it means that the filter on the engine has become clogged. Since contaminated fuel is better than no fuel the filter is bypassed letting fuel go directly to the engine. That's pretty much it. Hope this helps.  
Never take financial advice from co-workers.
 
nomadd22
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RE: Fuel Filter Bypass Warning

Thu Mar 10, 2011 4:07 pm

The thing that causes the bypass warning with fuel filters that have been properly maintained is usually contaminated fuel that clogged the filter way too soon. So, now you're running that same crappy fuel straight to the engines with no filtering.
I'd want to land as soon as possible too.
Anon
 
Mir
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RE: Fuel Filter Bypass Warning

Thu Mar 10, 2011 4:53 pm

A fuel filter bypass means that the fuel flowing to the engine is no longer flowing through the fuel filter (there's one per engine). This means that something is clogging the fuel filter, and the most likely cause of that is contaminated fuel. Continue running the fuel into the engines and there is a chance that you could either do damage to the engines, or have the engines shut down in flight.

There's not much you can do about this in the C525 - the checklist directs you to not transfer fuel unless absolutely necessary (especially if only one filter is showing the bypass), to expect partial or total loss of thrust, and to land as soon as practical (land as soon as possible if you've got the annunciator for both engines). If it happened to me, I'd be declaring an emergency and getting on the ground ASAP.

-Mir
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411A
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RE: Fuel Filter Bypass Warning

Thu Mar 10, 2011 8:34 pm

The penny-in-the-pail test of fuel, both before (especially) and after refueling, is still practised, by old time crews, worldwide.
IE: it works as advertised.
 
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jetmech
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RE: Fuel Filter Bypass Warning

Fri Mar 11, 2011 5:15 am

Quoting airkas1 (Thread starter):

Just to add to what the others have said, you can see the fuel filter and bypass in the lower left hand corner of the following picture;

http://home.roadrunner.com/~eastudio/images/fulepump.gif

Under normal operations, the ball check valve will be held against the left hand set by spring pressure. All the fuel must pass through the filter to get to the engine. There will be a pressure difference across the filter, which will be monitored by a differential pressure switch. This pressure differential will exist under normal operations, as a filter represents an obstruction, which demands a pressure drop to pass.

However, if the filter starts to become blocked, this pressure differential will rise. If the differential becomes high enough, it will raise the ball check valve off its seat and allow fuel to bypass the filter element. Once this pressure differential reaches some threshold value, it will trigger a "fuel bypass" warning.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
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airkas1
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RE: Fuel Filter Bypass Warning

Fri Mar 11, 2011 9:17 am

Awesome explanations guys! It's petty clear to me now.
Thanks!  
 
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HAWK21M
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RE: Fuel Filter Bypass Warning

Sat Mar 12, 2011 11:07 am

Fuel filter bypass indication is when the Fuel does not flow thru the fuel filter but bypasses it to prevent fuel starvation.
Cause could be clogged/contaminated filter.

Jetmech.....Fantastic animation....Where is this from....some CBT?.

regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
nomadd22
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RE: Fuel Filter Bypass Warning

Sat Mar 12, 2011 1:24 pm

Quoting HAWK21M (Reply 7):
Jetmech.....Fantastic animation....Where is this from....some CBT?.

How do you know he didn't just make it up on the spot for this thread?
Anon
 
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HAWK21M
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RE: Fuel Filter Bypass Warning

Sat Mar 12, 2011 6:36 pm

Quoting nomadd22 (Reply 8):

How do you know he didn't just make it up on the spot for this thread?

Knowing jetmech & his detailed explanations with Schematics/pics ......Thats a possibility  

regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
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larshjort
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RE: Fuel Filter Bypass Warning

Sat Mar 12, 2011 9:24 pm

Quoting nomadd22 (Reply 8):

How do you know he didn't just make it up on the spot for this thread?

The "Gary D. Baker ® 93" in the lower left corner might be a hint 

But I agree with HAWK21M

Quoting HAWK21M (Reply 9):

Knowing jetmech & his detailed explanations with Schematics/pics ......Thats a possibility

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tb727
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RE: Fuel Filter Bypass Warning

Sat Mar 12, 2011 10:18 pm

That's a pretty good animation of how it all works. I want to say I remember seeing it before in Lear ground school, that basically looks like the TFE731 system on the 30 series.
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