Could have been bad!

[Towner]

Had a hose change at annual in December. Not much flying since then, but the few times I went, I noticed a light fuel smell in the cabin when I first opened the door. Looked around, pulled the cowl, checked wing areas, pulled lower center panel and checked shut-off valve. Nothing. I had added a little fuel each time, so I thought maybe I was smelling fuel on my hands or something. Flew it a few times a never noticed a fuel smell while flying (probably to much ventilation coming through).

Today, the smell was a little stronger and I hadn’t touch fuel, so I went digging a little deeper. Started pulling things apart. Pulled lower center panel to check shut-off valve. Still looked good, but as I ran my hand up the hose towards the firewall, felt a drip. Pulled the center panel with the radios so I could see. While pulling the panel, the hose from the firewall to the shut off valve came completely off. I’m guessing the wires around it were holding it on, or pulled it off. There was no tension when pulling the panel, so whatever it was, it took next to nothing for the hose to come off. The band-it clamp was clamped around the fitting beyond the hose, with nothing holding the hose on except the hose itself. Got pretty lucky I was on the ground and that it didn’t come off during prior flights.
 

My question is about the fuel dumped into the cabin. Since I was chasing an odor or leak, I didn’t have the fuel hoses crimped. When the fuel hose came off, it started dumping fuel into the cabin until I saw where it was coming from and got my thumb over it. I’m guessing it dumped at least 1/2 gallon, probably closer to a gallon, into the cabin. Thankfully, I don’t think it got on any of the avionics since the panels were pulled forward. My concern is any other damage this may have caused by the fuel. Obviously the wires were soaked. It went into the pilots side floor and storage. Also saw some draining from the bottom of the fuselage behind the cabin.

Is there anything I should look for, be concerned about, or check? Needless to say, the hose is back on an properly clamped.

The mechanic has a pretty good reputation with these planes, so it just shows it can happen to anyone!

[Madhatter]

That's exactly why I changed all my hoses in the cabin to AN fittings. The current system is prone to design induced failure. Sure there are those that can install the fuel lines properly but it is still a very poor design and requires careful installation. Some have told me this has never been an issue, well now it has. I'm glad you weren't a descending fireball. 

[Warmi]

A few year back I had oetiker clamp fail while climbing out … thankfully nothing happened….this was a few months after 5 year rubber replacement and it appears my ( former) mechanic tried to reuse a clamp … when I took a closer look, it looked pretty mangled ..

 

[Steve Moliterno]

It's not fun when the fuel leak is behind the panel.

FYI, my mechanic discovered on my last years annual my fuel shut off valve has a small drip whenever it's not fully open and not fully closed.

 

 

[GrassStripFlyBoy]

11 hours ago, Towner said:

The band-it clamp was clamped around the fitting beyond the hose, with nothing holding the hose on except the hose itself

Sounds like the new hose was not on all the way, and mechanic blindly applied the band-it to the fitting missing the hose.  Was there fire sleeve over this line hiding it from visually seeing the issue or something?  Sounds like the diameter of the hose is also possibly a bit larger than stock?  I'm not a fan of band-it for that location, changed mine to a clamp.

[Tom Baker]

Was it the fitting before or after the fuel valve? What size was the hose? I use Oetiker clamps on pretty all of the fuel lines with a few exceptions. I use Norma fuel injection clamps where removal of the fuel line is a normal part of maintenance. I use Band-its where clearance is an issue. 

On the bright side our airplanes are very resistant to chemicals, so likely there should be no structural issues. Clean it up the best you can, and let it air out.

[Madhatter]

[Towner]

Thanks Tom. That’s what I was really concerned about. I knew a little fuel wouldn’t hurt anything, but I was worried about a large quantity puddling up somewhere I couldn’t see it. Cleaned it up the best I could, and left it to air out. Composite is still new to me after 2 years of owning it.

It was the feed line going to the shut off valve, where it attaches on the inside of the firewall.

As far as the clamp, it was just a miss. Clamp was put on just beyond the hose. Quality mechanic, he just missed one. I don’t know of mechanic that can say they haven’t made a mistake; cars, motorcycles or airplanes. And since the hose actually came off, it did it at the perfect time; sitting in the hanger. Other than a mess, everything is fine and clamp is secured.

Thanks for all the input from everyone.

[Tom Baker]

Again, what size hose? In my experience the correct 7.5mm hose takes significant force to pull off the fitting, even without a clamp. The 5/16" hose will fall of almost on its own.

[airhound]

Are other composite aircraft designs capable of, “behind panel” fire extinguishing”?   

[Towner]

2 hours ago, Tom Baker said:

Again, what size hose? In my experience the correct 7.5mm hose takes significant force to pull off the fitting, even without a clamp. The 5/16" hose will fall of almost on its own.

I’m really not sure what size hose. I’m guessing it’s a 5/16” because it slipped on without any force, but I’m not sure.

[Tom Baker]

1 hour ago, Towner said:

I’m really not sure what size hose. I’m guessing it’s a 5/16” because it slipped on without any force, but I’m not sure.

That is why I have been an advocate of using the correct size fuel hose, instead of the 5/16" substitute. Attached is a picture of the fitting in question. With the correct size hose slid on to the end of the clamping area it takes 12 pounds of pulling force for the hose to slowly slide off the fitting. With the 5/16" hose slid on the the same spot I can not get a pull force reading, because the weight of the scale will cause the hose to slide off. If you slide the correct size hose 1/2" past the clamping area it take over 50 pounds of force to remove the hose. Actually my scale goes to 50, and the hose did not budge. The 5/16" hose does have some resistance when it is slid on that far, but it will start sliding with about 20 pounds of pressure. Once it gets to the clamping area, then it just falls off. The 5/16" hose does not fit the barb with enough pressure to prevent leaking without a clamp.

[Towner]

2 hours ago, Tom Baker said:

That is why I have been an advocate of using the correct size fuel hose, instead of the 5/16" substitute. Attached is a picture of the fitting in question. With the correct size hose slid on to the end of the clamping area it takes 12 pounds of pulling force for the hose to slowly slide off the fitting. With the 5/16" hose slid on the the same spot I can not get a pull force reading, because the weight of the scale will cause the hose to slide off. If you slide the correct size hose 1/2" past the clamping area it take over 50 pounds of force to remove the hose. Actually my scale goes to 50, and the hose did not budge. The 5/16" hose does have some resistance when it is slid on that far, but it will start sliding with about 20 pounds of pressure. Once it gets to the clamping area, then it just falls off. The 5/16" hose does not fit the barb with enough pressure to prevent leaking without a clamp.

As always, thanks for the info!

[Roger Lee]

FD European metric hose is 7.5mm and 5/16" ( 7.9mm). Four tenths of one mm should not make any difference in our hose choice. Think about how small 4/10th of one mm is.The one issue is that FD came out with those fittings really meant for 1/4" hose which is 6.3mm. Later on they came out with larger metal fittings more correct for 5/16" - 7.5mm.   7.5mm for this fitting is technically to big too.

This said if you push the 5/16" / 7.5mm up past the first 1/2" onto the shaft past where the indentation is it fits much better and if you use a smaller than normal Oetiker clamp or a fuel injection clamp 5/16" hose works just fine and has been since 2007 when these metal fittings first came out with the new firewall blanket. FD used to just pass the rubber hose through the firewall. The huge majority use 5/16". Besides 1/4" hose 5/16" is all I use. When clamped PROPERLY it will never leak or come off.

[Skunkworks85]

44 minutes ago, Roger Lee said:

FD European metric hose is 7.5mm and 5/16" ( 7.9mm). Four tenths of one mm should not make any difference in our hose choice. Think about how small 4/10th of one mm is.The one issue is that FD came out with those fittings really meant for 1/4" hose which is 6.3mm. Later on they came out with larger metal fittings more correct for 5/16" - 7.5mm.   7.5mm for this fitting is technically to big too.

This said if you push the 5/16" / 7.5mm up past the first 1/2" onto the shaft past where the indentation is it fits much better and if you use a smaller than normal Oetiker clamp or a fuel injection clamp 5/16" hose works just fine and has been since 2007 when these metal fittings first came out with the new firewall blanket. FD used to just pass the rubber hose through the firewall. The huge majority use 5/16". Besides 1/4" hose 5/16" is all I use. When clamped PROPERLY it will never leak or come off.

For a multitude of reasons, it is down right silly to not use the correct hose. I would Never install an incorrect hose size, or allow someone to do so.

[Roger Lee]

You'd have to show me the science that says the 5/16" with only a .4mm difference doesn't hold and seal as well as the 7.5mm 

I have an idea. While out at the hangar today I'll see if I can make a test and video? When I usually test hose fittings I put the fitting in a vise and expect the hose to rip before it comes off a fitting. Even those both of these hoses work without leaking or other issues I would bet a bunch of money that both will pull off the fitting with some force which isn't there during its normal installation. We'll see.

Plus if you think like this then most things you buy in America isn't what was on your original engine. Then using our 1" coolant hose vs 25mm is different or our oil hose here is a few tenths different. 1/4" fuel hose is different. They use metric on everything. Even using different batteries. It all works.

People have been doing this for decades here in the US since we don't usually have metric items laying about. 

It isn't 100% just the size, but the fit and function after installation.

Just so you know we started talking about that "Y" and straight metal fitting through the firewall. The 7.5mm hose is too big for that too. The fitting supplied was just too small at that application point. This is why later on FD made the fittings larger. I carry both sizes.

[Tom Baker]

10 hours ago, Roger Lee said:

FD European metric hose is 7.5mm and 5/16" ( 7.9mm). Four tenths of one mm should not make any difference in our hose choice. Think about how small 4/10th of one mm is.The one issue is that FD came out with those fittings really meant for 1/4" hose which is 6.3mm. Later on they came out with larger metal fittings more correct for 5/16" - 7.5mm.   7.5mm for this fitting is technically to big too.

This said if you push the 5/16" / 7.5mm up past the first 1/2" onto the shaft past where the indentation is it fits much better and if you use a smaller than normal Oetiker clamp or a fuel injection clamp 5/16" hose works just fine and has been since 2007 when these metal fittings first came out with the new firewall blanket. FD used to just pass the rubber hose through the firewall. The huge majority use 5/16". Besides 1/4" hose 5/16" is all I use. When clamped PROPERLY it will never leak or come off.

I didn't say it fits much better, I said it has some resistance. What are the legal ramifications for using a fuel line size other than whet is spelled out in the parts manual? does it make the airplane un-airworthy? I wouldn't want to try and defend my position from the witness stand. There is no advantage for using the 5/16" hose over the correct size other than cost, and the cost differential from my current supplier is less than $10 per airplane. 

[Tom Baker]

4 minutes ago, Roger Lee said:

You'd have to show me the science that says the 5/16" with only a .4mm difference doesn't hold and seal as well as the 7.5mm 

I have an idea. While out at the hangar today I'll see if I can make a test and video? When I usually test hose fittings I put the fitting in a vise and expect the hose to rip before it comes off a fitting. Even those both of these hoses work without leaking or other issues I would bet a bunch of money that both will pull off the fitting with some force which isn't there during its normal installation. We'll see.

Plus if you think like this then most things you buy in America isn't what was on your original engine. Then using our 1" coolant hose vs 25mm is different or our oil hose here is a few tenths different. 1/4" fuel hose is different. They use metric on everything. Even using different batteries. It all works.

People have been doing this for decades here in the US since we don't usually have metric items laying about. 

It isn't 100% just the size, but the fit and function after installation.

Just so you know we started talking about that "Y" and straight metal fitting through the firewall. The 7.5mm hose is too big for that too. The fitting supplied was just too small at that application point. This is why later on FD made the fittings larger. I carry both sizes.

I didn't do a video, but I did actually do a pull test with a scale. The 5/16" hose does not fit the fitting. 

You are correct that the 1" coolant hose is not 25mm like the original, but there is an approval to use it. There is no such approval for the fuel hose.

I only use Rotax oil hose, I don't think its size is off. I don't use the Aeroquip oil hose because there are some fittings on some airplanes that it will slide off, just like the fuel line. That led to an parachute pull and total airplane for a member here.

[procharger]

Clamp it properly  it will be no issue I use screw clamps you will not pull it off.

[Madhatter]

The bottom line is the tube design is wrong. The tube is undercut to create the beaded end, it's just cheaper to do it that way but it can be prone to leaks depending on the installer. I have never seen a beaded tube end done this way on any aircraft ever.

[Towner]

Well, I’m still not sure what size hose it is. With the clamp on it now, it will not come off. Doesn’t mean I won’t look at the hose size and consider changing it next time I’m in there, but for now, I’m very comfortable with it staying on and not leaking.

[Roger Lee]

Okay real time video evidence that the difference from the 7.5mm vs 5/16" (7.9mm) which is only ,4mm difference make zero difference. I pulled so hard my work bench was shaking. Science and research is always better than conjecture. 

 

[Tom Baker]

Roger, no conjecture on my part. The hose should seal on the fitting without a clamp. If you are relying on the clamp for the seal something is wrong. I was working out of town today, buy I will post a video tomorrow. 

[Roger Lee]

10 hours ago, Tom Baker said:

Roger, no conjecture on my part. The hose should seal on the fitting without a clamp. If you are relying on the clamp for the seal something is wrong. I was working out of town today, buy I will post a video tomorrow. 

 

The main thing is you'd never put a hose on without a clamp so it really shouldn't be an issue. It's not a real scenario.

Both hoses would seal the SAME without the clamp, but that isn't real life because we always use clamps. The clamp only keeps it from coming off and of course gives a better seal. They both felt the same friction when applying them and pulling them off after I cut the clamp. .4mm makes no difference. I can make a fluid induced video. All hose make a better seal with a clamp or we would never need the clamp.

[Tom Baker]

9 hours ago, Roger Lee said:

 

The main thing is you'd never put a hose on without a clamp so it really shouldn't be an issue. It's not a real scenario.

Both hoses would seal the SAME without the clamp, but that isn't real life because we always use clamps. The clamp only keeps it from coming off and of course gives a better seal. They both felt the same friction when applying them and pulling them off after I cut the clamp. .4mm makes no difference. I can make a fluid induced video. All hose make a better seal with a clamp or we would never need the clamp.

Roger, I suggest you do a little research into how a rubber hose seals on a barbed fittings. Rubber hoses are pliable. The the hose should compress as it slides over the ramp of the fitting causing it to seal, not because of the clamp. That .4mm is the difference between the hose sealing like it should, and not sealing at all. The purpose of the clamp in not to provide the sealing force. In low pressure system like ours all of the fitting should seal without clamps installed. The reason we install clamps is because of outside and sometimes internal forces trying to remove the hose from the fitting. As hoses age they can lose pliability, and in this case the clamp is an added safety feature.

I pulled this from a simple search explaining how this type fitting should work. 

Sealing for single 'smooth' ramp single flute barbs takes place along both the increasing diameter ramp surface and at the peak of the single flute. That type of fitting often has an area for an external clamp. And the instructions for those fittings will offer something like "Do not place clamp on top of the barb."