Fuel line failure

[n5lp]

Yesterday, after I shut down, I noticed fuel dripping from the cowl air outlet. Today I investigated and found that an aluminum line from a tee, downstream of the fuel flow transducer to the fuel pressure transducer, was leaking a large volume of fuel. It required removing the line to find the source of the leak.



The aluminum line was cracked at the edge of the sleeve. The crack is through the order of 150 degrees of the line. This was invisible from the outside of the line, but could be seen on the inside.



Both the fuel flow transducer and the pressure transducer are mounted to the engine mount with home fabricated aluminum brackets mounted to the engine mount with adel clamps. The length of the failed tubing is 4 1/4 inches.



The RV-6 has around 1,000 hours and was built at a time of no firewall forward instructions or kits by someone with no background in these arts.

The best guess of me and my cohorts is that the mounting of the fuel pressure transducer was flexible enough to allow a resonant vibration that over time cracked the line at the edge of the ferrule.

Those with more knowledge can supply their analysis.

I fabricated all the fuel and oil lines on my airplane, but my plan is to order a flexible line to replace this one. I will need to move the pressure transducer to allow enough space for this.

[Ironflight]

Great post Larry - and very glad that you found this on the ground!

It does go to show that we need to be very thorough when we do our condition inspections, as I know that you are. Some things you just don't find unless you take them apart. the other good point is that 1,000 hours is actually a fair amount of time for the average RV - when you get out that far, it is really time to look close at things like the fuel system - things that can really ruin your day!

When I do tech Counselor visits, I am rarely worried about an V's primary structure - it is pretty hard to screw it up. Were I spend my time is looking at the systems - primarily fuel and oil line plumbing. And personally, I have a large collection of "bad" flare ends from when I plumbed my own airplane - I flair them, look at them closely, and frequently cut off the end and do it again.

Fire in flight is probably the worst thing I can imagine, and I take NO chances with my fuel system.

Get it fixed, and get back into the air Larry!

Paul

[N941WR]

Originally Posted by n5lp

I fabricated all the fuel and oil lines on my airplane, but my plan is to order a flexible line to replace this one. I will need to move the pressure transducer to allow enough space for this.

Here is a question, which is better, flexible lines or formed aluminum lines?

It is my understanding that flexible lines need to be replaced every so many years and yet there is no expiration date on hard lines.

[Geico266]

Great catch. These machines need constant vigilance & surveillance.

Could you smell the raw gas in the cabin, or on the ground? One of the ways I "inspect" is with my nose. Anything different than the last flight gets special attention. Come to think of it, I must look pretty strange sniffing my plane!

[n5lp]

Originally Posted by Geico266

...Could you smell the raw gas in the cabin, or on the ground? One of the ways I "inspect" is with my nose. Anything different than the last flight gets special attention. Come to think of it, I must look pretty strange sniffing my plane!

I have smelled fuel in my plane before (never in flight) when the tank selector valve was seeping but I didn't smell anything at all on this flight. I think it was an inflight failure.

[mannanj]

Originally Posted by N941WR

Here is a question, which is better, flexible lines or formed aluminum lines?

It is my understanding that flexible lines need to be replaced every so many years and yet there is no expiration date on hard lines.

Bill:

Replace flex lines at specified intervals, replace solid lines when they break.

Not trying to be a smart a$$. My personal choice is flex for anything forward of the firewall, and about a 12 in. flex for the brakes between the solid lines down the gear leg and the calipers.

Inspect, inspect, inspect. Did I say "inspect"?

[AlexPeterson]

Originally Posted by N941WR

Here is a question, which is better, flexible lines or formed aluminum lines?

snip

I would think that aluminum lines which are rigidly attached to non-relative motions structures would always be preferred to flexible lines.

It seems that Larry is correct - there was some sort of relative motion between the flow transducer and the other end of that aluminum tube.

Whew!