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Check those fittings

kaa

Well Known Member
Not sure if there is anything new to the story, but I just wanted to share.

I've always steered away from doing work on the fuel system of my plane (I didn't build it). However with the panel upgrade I had to change some fittings, and then I needed to replace the carb, so I kind of eased into it. Anyway, today I was fixing a tiny seepage in the main fuel line fitting on the carb (probably hadn't tightened the NPT adapter enough when I installed it). This all went fine, but to my surprise when I turned the fuel pump on the first thing I saw was a a small puddle of fuel on the floor.

Turns out that a fitting to the red cube was finger tight! See it on the picture - the fitting is just finger tight and the torque strip is as it was. I've never touched these fittings since they were installed by an A&P during condition inspection a year and a half ago, when all fuel lines were replaced. So it sounds like I was flying for more than a year with a main fuel line fitting just finger tight, and the only thing that prevented it from undoing itself was some tension that the fuel line put on the connection. When I was moving the line away to remove the carb fitting, it probably tugged on the red cube just enough. I checked everything else of course and it was fine, but still I'm not exactly happy about this.

The bottom line I guess is - even if there is a torque strip on something, doesn't mean that it is tight. Better check all of them!

I wonder how often it happens. I remember finding something like this on a rental Arrow a while ago (I think a gascolator was loose).
 

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since this is the fuel system, you may want to step back and take a look as to why the connection became loose. there may be a better arrangement to minimize the stress on that fitting. in general, straight fittings will provide more retention over a 45 degree and especially a 90 degree angle fitting. if at all possible, use straight fittings when connecting to vibrating devices. this fitting appears to be straight, so try to understand what is really going on here.
 
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since this is the fuel system, you may want to step back and take a look as to why the connection became loose. there may be a better arrangement to minimize the stress on that fitting.

It sounds like it was always loose because somebody never tightened it properly in the first place? If it had become loose afterwards then the torque strip should be out of alignment?

I've also experienced leaks and other faults after maintenance so I agree it is worth having a second set of eyes over anything that is critical.
 
Yeah, I think it has never been torqued. I don't really see another explanation for why the torque strip is aligned. Plus, it's difficult to explain how it can loosen to the point of finger-tight, but not more. It's also supported pretty well.
 
Yeah, I think it has never been torqued. I don't really see another explanation for why the torque strip is aligned. Plus, it's difficult to explain how it can loosen to the point of finger-tight, but not more. It's also supported pretty well.

I agree. This fitting was never properly torqued up in the first place. I've seen torque seal spin around without fracturing when it was applied to an oily thread and that of course can be dangerously deceptive. But in this case the torque seal looks securely bonded to both surfaces so no chance that the B-Nut has backed off to finger tight.
 
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I have seen torque-seal break free from one side and stay intact. It looks like you have a fitting that has never turned, but in fact you just have one side of the seal un-attached.
 
check those nuts

I guess this is a new one for Vic - check those fittings along with checking those nuts!

Really glad this happened on the ground - not sure fuel spraying on the exhaust during flight would have been very fun.
 
just goes to show you that anyone can overlook something. Dont assume its tight, the assumption could be catastrophic.

Tom
 
This got me thinking about something I'm doing at the moment.

I just installed my 2 gear mounts into the cabin. I torqued all of the bolts down. I then started applying torque seal. However, I only had time to do a portion of the nuts before my "work from home" lunch break was over. As a result I left the hangar with the job half done. This is probably not a good idea in general and I try not to do it, but in this case I did. I double checked all the bolts were torqued before starting the application of torque seal, but I could see that if I walked away from this for too long it could allow for an error to occur and it could result in something like the poster saw. So I might suggest that a good standard work practice would be: before applying torque seal to always confirm that the bolt/nut is torqued properly.
 
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