Some part of the fuel system busted. What's the takeaway?

SixPapaCharlie

SixPapaCharlie

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Was flying with my wife today and we smelled fuel. It's an old plane and sometimes we smell fuel but today it was strong.
We were in cruise and I had forgotten to lean the engine so I decided maybe I am sending too much go juice and its not all burning up and some unburned fuel maybe is coming out of the exhaust or something.
I leaned back and the smell seemed to go away. After about 5 min I asked do you still smell it and she said "I think a little but certainly not as bad as before. " I agreed it seemed significantly less..

We finished the flight and landed and went home. I drove back to the hangar to give everything a once over and noticed this:


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I have only ever seen blue like that around wing roots and tank sumps. I get underneath for a better look

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The nose gear well is blue. All over, like someone just splashed a pint of Low Lead up on there.
I call a MX and we talk through a few ideas and he says "Turn your fuel pump on and see if it is dripping" So I do and I see this:





My mechanic comes over to help me take a closer look and this Tee had snapped leaving part of it inside the elbow bracket (I don't know what anything is called)

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During preflight, I didn't see any fuel on the gear. Runup was fine, and actually the engine was smooth the whole flight. Wondering if I was a couple of bumps away from a much more dramatic day.

If you are in flight and detect a strong fuel smell, land immediately? In hindsight, that seems like it would have been the right action. However the odor reduced significantly after leaning the mixture so we were lulled I guess into thinking maybe it was a non issue.

I think if you smell fuel to the extent that you notice it and are asking others "Do you smell that?" land the plane and start looking for blue stains.
 
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No, I didn't put the tool marks on the tee but it sure looks like someone chewed it up.
I don't know what it should be made out of.

Engine doesn't vibrate too much. It did when I got it but I've had the motor mounts replaced and the prop balanced so vibration is minimal
 
Damn dude....that could've gone a lot worse. Glad it worked out.

Did you turn your fuel pump on for landing, and did it get noticeably worse then as well? All that gas...right next to the exhaust....:eek:

I'm not sure what takeaway there is other than airplanes break. And they're not getting any younger. My plane very often smells like gas when the tanks are totally full, but we can't find any leaks. I'm not sure I would've done things any differently than you. I suppose any sudden change is worth investigating.

That tee is pretty beat up. Wonder if some ham fisted mechanic over-tightened the bejeezus out of it at some point, setting the stage for the failure.
 
Was that fitting attached to the aux pump or the engine pump?
 
Engine pump. My understanding is on this setup they are in line and the aux pump really just pressurizes the area between itself and the engine mechanical pump
 
Dan Thomas said:
Was that fitting attached to the aux pump or the engine pump?
Click to expand...

Building on where (I think) Dan is headed: There is plenty of anecdotal evidence (with engineering behind it) that aluminum fittings are a bad idea FWF for anything subject to vibration or movement.
 
these old planes leak like old harleys. except yours, that is not very harley-like. it's different.
 
Dude, you smell raw fuel in the cockpit during cruise, you get the plane on the ground. Now. Well, at least at the closest strip that's safe.

JMO
 
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Vibration is the single greatest risk to the GA airplane. This is a great example, and why we have to inspect the crud out of these marvelous beasts.

I’m very glad you’re ok, because (and I ain’t joking) a leak like that could lead to a terrible fire.

—-

Edit: What Salty said ^^^.
 
SixPapaCharlie said:
No, I didn't put the tool marks on the tee but it sure looks like someone chewed it up.
I don't know what it should be made out of.

Engine doesn't vibrate too much. It did when I got it but I've had the motor mounts replaced and the prop balanced so vibration is minimal
Click to expand...
Sorry I deleted my post by accident.

Is that a pressure snubber fitting it is attached to?
 
Man, that could have been bad. Glad you’re okay.

Whaddaya bet that it had a little weepage and someone “fixed” it by over tightening the crap out of it? Go over that entire fuel system carefully. This might not be the only ham fisted example. Be suspicious of tool marks.
 
I also had a t-fitting crack; mine was under the floorboards and pretty beefy; -8 as I recall.
It went to the aux fuse tank.
It was so much more robust then the B-nuts & hardlines, I didn’t think it was a mx error.
 
The saving grace was that the leak wasn't likely that prominent with the engine running, especially at cruise speeds. With the engine off and not consuming fuel, the pressure from the aux fuel pump will certainly make it spray out further. However, that scenario would have been ripe during final approach where you have the aux fuel pump on and low engine speed. In-flight fires would be no bueno. New t-fitting and you should be good to go, although I'm surprised it isn't an AN fitting.
 
The first flight after getting a new carb and fuel lines installed, I noticed a strong fuel odor. Looked down and my fuel pressure started dropping off. It was probably only about 1lb of pressure and I made a 180 back to the airport. Come to find out, a nut on one of the fuel lines wasn’t torqued enough and it was peeing fuel out. The smell of fuel in flight gets your attention quick, and yes, get on the group asap.
 
SixPapaCharlie said:
Engine pump. My understanding is on this setup they are in line and the aux pump really just pressurizes the area between itself and the engine mechanical pump
Click to expand...
Vibration did that. Fittings stuck together like that, with hoses hanging off them, put a lot of stress on the fittings nearest the source of the shake, and they crack at the threads.

Continental made a booboo when they did the plumbing for the oil on the engines in the Cessna 400 and, I think, the Cirrus SR22T. They had a stackup of fittings all handing off a 1/4" NPT nipple in the oil cooler, and engine vibration cracked that nipple and there was at least one failure due to oil loss. The setup was to provide oil to the turbo and wastegate, and to carry an oil pressure switch. Someone in engineering obviously wasn't thinking about vibration; after all, vibration is the responsibility of engineers who specialize in that, right?

In the TCM service bulletin http://www.tcmlink.com/pdf2/CSB15-7B.pdf We see this:

upload_2023-5-21_21-42-4.png
The bushing at top left screwed into the oil cooler, which is mounted on the left side of the engine and so this stuff gets shaken up and down all the time as the engine vibrates around its crank axis, sometime quite violently.

The SB turned into an AD: https://drs.faa.gov/browse/excelExternalWindow/119AF17054BD08C58625804C0051FD49.0001

From the preamble to the AD:

upload_2023-5-21_21-48-30.png
 
RyanB said:
Come to find out, a nut on one of the fuel lines wasn’t torqued enough
Click to expand...

I have to wonder how many b-nuts receive proper torque.
A) you need to use crowsfeet and how many bother....even when they do have them....even when there is enough room to get one in there.
B) you have to do some calculations....and from the arithmetic many mech's have, I wouldn't be shocked by egregious errors in that department.
C) The torque values on b-nuts seems crazy-high to me, especially the larger ones.
 
When I first got my bonanza I started to smell fuel while doing practice approaches one day. Immediately landed and sniff tested out to the fuel selector. Pulled everything off and the flare had broken in the b nut on the fuel line that leaves the selector to the engine! Glad nothing worse happened!
 
A few times I had to find tiny fuel leaks that were causing odors. They can be notoriously hard to find unless they've been leaking long enough to leave a blue stain. The fuel will evaporate as fast as it leaks out and so no wetness is seen, and the odor is everywhere and you can't pinpoint it.

So I took about 30" of 1/4" poly tubing and a bit of thin rubber diaphragm material and made a sniffer. I formed the rubber into a funnel that taped onto one end of the tubing, and cut its open into into a profile that fit fairly closely over my nose. Now I could suck in air that was coming only from the other end of that tube, and by running that end over the various lines and fittings I'd get a good blast of fuel stink that instantly located the leak.

I know, gas sniffer jokes... heard them all...
 
Glad you and the plane are OK and that you posted the story. My take aways are - land if you smell gas, and that the blue dye sure works pretty well.
 
So.... I am looking at the replacement Tee.
I see it comes in Aluminum and Steel
The Elbow comes in Aluminum and Brass

What variety of parts should I get? My MX says doesn't matter. His 250 has aluminum.
I feel like I should get the steel variant and no idea on the elbow.
Price difference is negligible.
 
Domenick said:
I have two fuel gauges and don't use them. I fly by time assuming the POH's 9 gph. I've never hit 9 gph.
Click to expand...
This scenario is a good reason to use the gauges also. A clock won’t notice a leak but the gauges will.
 
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SixPapaCharlie said:
So.... I am looking at the replacement Tee.
I see it comes in Aluminum and Steel
The Elbow comes in Aluminum and Brass

What variety of parts should I get? My MX says doesn't matter. His 250 has aluminum.
I feel like I should get the steel variant and no idea on the elbow.
Price difference is negligible.
Click to expand...

I'm not sure how dissimilar metals would affect this. I've got an aluminum hose permanetly corroded onto a brass hose bib due to dissimilar metal interactions.
 
SixPapaCharlie said:
So.... I am looking at the replacement Tee.
I see it comes in Aluminum and Steel
The Elbow comes in Aluminum and Brass

What variety of parts should I get? My MX says doesn't matter. His 250 has aluminum.
I feel like I should get the steel variant and no idea on the elbow.
Price difference is negligible.
Click to expand...
The parts catalog will tell you what to use there. Using what was found there risks repeating the mistakes of past mechanics. Cessna uses steel fittings in places like that.

If you don't have the parts catalog, there might be one online as a .pdf, for free. Google it. And download it if you find it.
 
Dan Thomas said:
The parts catalog will tell you what to use there. Using what was found there risks repeating the mistakes of past mechanics. Cessna uses steel fittings in places like that.

If you don't have the parts catalog, there might be one online as a .pdf, for free. Google it. And download it if you find it.
Click to expand...

Thank you!
The parts catalog calls for aluminum
 
SixPapaCharlie said:
Thank you!
The parts catalog calls for aluminum
Click to expand...
OK. See what the mechanic can do to relieve the strain on the fittings. Long lengths of hose hanging off them could be clamped to the engine, near the fitting, to take the strain off the fittings. Short lengths of hose yanking on the fitting when the engine moves should be replaced with lengths mentioned in the parts catalog.

Old airplanes are full of mistakes. 40 and 50 and 60 years give a lot of time for that to happen, and one mechanic's mistake can be carried forward and repeated for decades.

And see that the fittings are torqued as per standard practices. Too tight is as bad as too loose. Overtorquing starts cracks.
 
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