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Loose Fuel Line Fittings, a very close call !!!

Walt

Well Known Member
This guy was extremely lucky, he asked me to do a prop balance and check for what he thought may be a vaccum leak because the engine was running "a little rough" (the aircraft had recently made a long cross country trip into our airport).

Well when I taxed the aircraft over to do the balance I could barely keep the thing running unless I kept working the throttle. No way I could balance this thing without fixing whatever was going on first. After about a 2 minute taxi over to my hanger, I shut it down and proceed to do a preliminary inspection.

It didn't take me to long to spot the rather large fuel puddle that had already accumulated on top of the airbox and fuel dripping everywhere. Further investigation revealed that the 'B' nut on the fuel manifold was loose and fuel was spraying on the engine block and running down the fuel line inside the fire sleeve :eek:

Keep in mind the fuel pressure in this line at idle speeds is just a few PSI, at high power settings the pressure goes much higher. I had a really good leak going at idle, at full power, fuel would have been spraying everywhere.

This is why I always say: put a wrench on all critical bolts and fittings everytime you do an oil change or at least every condition inspection. Merely looking at things is not good enough!!!

Somebody was watching over this guy....

leak1.gif


Here's the 'B' nut that was loose, you can see behind it all the blue on the bracket and engine case. Fuel was also running down inside the fire sleeve. The top of the fire sleeve "had" red silicone sealing it, I peeled it away to inspect the hose fittings (it was loose and coming off anyway at this point from being soaked in fuel).

leak2.gif


Needless to say I checked the rest of the fuel lines FWF and found a few others that were under torqued.

The prop balance came out good: from a very high 0.523 to nice 0.022 IPS :D

Be safe out there folks, and take care of your machine.
 
Thanks!

Walt,
Thanks for the pictures and explanation. I am sure someone will learn from this and take heed of your warning.
The A&P that did the pre-purchase inspection on my 6A told me to never say "I HAVE to take the cowling off", but rather "I GET to take the cowling off" and to use every opportunity to look over the FWF.
This prevented something very bad from happening to me recently when I caught a bent push rod during an oil change! (Engine had ran great without any issues!)

Dan
 
First of all, I want to give Walt a HUGE THANK YOU for finding this.

The issue was on my airplane and here is the backstory. This airplane has just a tad under 100 hrs total time, and has been a perfect runner the entire time I have owned it. I took the airplane to Walt's field to get the airplane painted at Glo-Custom in the middle of Feb. On the last leg of three from the Farm, I noticed that the fuel flow was very slowly creeping up. The engine was running fine, and the EGT's were stable at 30 deg LOP. The only indication of an issue was the .75 to 1 GPH higher fuel flow, and a sub normal #3 CHT. There was NO smell of fuel at all, and the heat was on. On landing at 52F I could barely keep the engine running for the short taxi to Grady's, and now had some real concerns about the return trip in six weeks. I had already set up with Walt to do the prop balance, and to fix a tank leak. I also asked him to investigate what I thought was an induction system leak (no fuel smell at all) , as that was what I thought might be the problem. I was obviously not going to fly the airplane again until these issues were resolved. Walt emailed me last night with the prop balance results and what he found with the fuel line. That was an OMG moment if there ever was one.

It seems obvious that the B nut was under tourqued and that over time it had been vibrating loose. It finally got loose enough to spray fuel on that last leg. Now as Walt said, someone was looking out for me, because the fitting was spraying fuel at some rate for the better part of an hour. Only providence could have kept that airplane from catching on fire.

So folks, take Walt's advice to heart and check stuff every time the cowl is off or other things are open on the airplane. I KNOW I certainly will.

I will end this missive by saying again that Walt has jumped to the very top of my good guy list. He is a wonderful resource for all of us in the Van's world, especially us RV newbies.
 
Mike---you are a very lucky guy. Looks like the builder used 701 hose, and a NYLON tie wrap to secure the firesleeve? suggestion---fix it right. Walt can do that.
Tom
 
A guy brought me a 210A one time that had a leaking diaphragm on the flow divider. Old style divider with pinhole instead of drain line. It had been leaking so long that it and the top of the case were encapsulated in blue putty. When I scraped off the putty, I found a chunk of crankcase and one bolt torn out and epoxied back into place. Someone had tried to lift the plane by the engine hoist loop after a gear-up and tore a chunk out of the case. A skysmasher I worked on had 3 injector lines chafed through on the rear engine that were shooting fuel everywhere. No way all 3 lines chafed through at once. I guess you take your luck where you find it.
 
Mike---you are a very lucky guy. Looks like the builder used 701 hose, and a NYLON tie wrap to secure the firesleeve? suggestion---fix it right. Tom

I agree with Tom, when you get back to your home base I would recommend, as soon as practical, you pull all the fuel/oil hoses and send them to Tom for duplication with properly fire sleeved Teflon hoses with swaged fittings.
 
Torque seal is another great low cost product to help in visual verification of torque.

Torque seal will only show if relative motion has occured between the painted surfaces, it does not show "torque". In the case of a sheared bolt head for example (which I have seen) "torque seal" will still look good but obviously will not be representitive of torque. Broken bolts can only be found using a wrench (although sometimes you will find the head laying somewhere and now you must search for the origin).

I learned "inspection" from an old geezer that told me you must inspect with all your senses, especially feel, not just by looking. This motto has served me well over the years.

When I inspect an airplane torque seal don't mean didly to me, for all I know you marked it "by accident". Nobody leaves fuel lines loose on purpose, so don't tell me it can't happen.
 
Torque seal is another great low cost product to help in visual verification of torque.

Walt, thanks for shooting me down. You will note in the above quote that it will "help" in the verification. I did not say it was the end all to all problems. Your original post stated that the B-nuts had backed off their torque. In that situation, torque seal, if it was applied properly would have easily indicated that condition. I work on and fly OH-58 and UH-1 helicopters. With the extreme vibratory conditions, our lines are marked with torque seal. During pre-flight, it provides a quick visual condition indicator along with physically checking the lines. I have personally located a perfectly torqued, torqued striped, B-nut that when I tugged on the line, the line came out in my hand. The stainless tubing had failed at the base of the flare. Torque seal did its job, but that wasn't the problem area. The problem was the failure of the tubing. I have also found nuts that have backed off their torque and was quickly noticed by the broken torque striped line. This was similar to what you described. I was merely adding a low-cost additional safety step that people can use in determining if their aircraft is safe to fly. It is imperitive to understand what torque seal does, and it's limitations. If you don't fully grasp it's function, don't use it. I have over 25 years experience in maintenance with a foundation started in army helicopters. In the army, everyone of the un-safetied nuts on my helicopter was torqued striped. This has continued into my current law-enforcement job and into the construction of my own RV. The proper application requires one to torque the part and immediately apply the torque stripe. The practice of merrily painting away of the fittings isn't even considered. And no, Walt, I have never just painted a nut without first torquing it. If you did do that, then I could see what you said could happen. The discipline of the Army and hopefully for any A&P would dictate that they not do that. Many peoples (A&P's) standards vary, but for the above stated reasons, I insist on using torque seal as another tool in the chain of safety of flight. I truely hope some of the other RV'ers would consider the same and not be discouraged by the berating of the subject in your previous post.
 
Greg: Interesting, I didn't take Walt's post as berating at all, merely adding information which you subsequently agreed with. I think you two are on the same sheet of music.

All good info. :cool:
 
I learned "inspection" from an old geezer that told me you must inspect with all your senses, especially feel, not just by looking. This motto has served me well over the years.

.

So now you're the old geezer :)
 
guess we take things differently

Pete,
I guess we see things differently in reading Walts response. Maybe if all of us carefully read a post before we respond, this will be a much nicer place to be.

Greg, as the son of an Army AH-64 Longbow pilot, I would like to thank you for the service and care you took when servicing the helicopters for our armed forces. My son also flew the 58's while training at Rucker. Im sure you are taking the same care with the planes you work on now. I wish I was closer to TN, I would bring my plane to you anytime.

rockwood shepard
glenwood springs CO
 
Greg - My apologies if I offended, I could have worded my response better.

It wasn't my intent to shoot down using torques stripes, only that torque striping should not be the only method used to verify torque on critical items.

I do agree that using torque seal is a good way to keep track of things.

In the airline world (which I grew up in) only the "inspector" was allowed to use torque seal, and he only did this after he personally observed the torque process or checked the torque himself. So for critical items torque was always physically verified by 2 people, the mechanic and inspector before seal was applied.

The intent of my post was simply to get people in the habit of not relying solely on torque seal for an inspection technique or as a means to avoid getting their hands dirty.

The experimental world is quite a bit differnent and "undisciplined" from world from we both come from (airlne and army), I am just trying to instill some good practices that you and I both take for granted.

PS: My son is in the Army so I love the Army!
 
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Greg: Interesting, I didn't take Walt's post as berating at all, merely adding information which you subsequently agreed with. I think you two are on the same sheet of music.

All good info. :cool:

Yes, but the part about torque seal meaning diddly kindda rubs me the wrong way and I think Walt could have been a little clearer in his meaning. I understand where he's coming from, but the torque seal does have a very big role in maintenance. If I had an unfamiliar aircraft roll up with torque stripe covering everything then I can see and understand Walt's reluctance to depend on it. And, the above scenarios do have validity without doubt. For the average homebuilder here that does his or her own maintenance, then torque seal will be of great benefit. Any abnormality will stand out.

To be fair to Walt, we need to define what torque seal is and what its mission is for in case some one on here is new to it. Torque seal is a colored inspection lacquer that dries hard. One can paint a stripe from the fitting to the nut and create a bridge that dries hard. If applied correctly, any movement of the nut will cause the stripe to break indicating movement. However, before you stripe the nut, the nut must be brought up to the correct torque and then the torque seal applied. If you under torque it or not torque it at all, then the stripe will dutifully be a record of the event till it moves from that position. As both of us has stated, other things can happen under the striped piece without any indication of anything wrong by the torque stripe. Its an indicator, not insurance.

The proper way to use it is to torque the item and then stripe it to verify you have torqued it. When you have completed your task, you now have a visual indicater that you did torque all the items. If the one maintenance person goes back at a later time and sees a broken stripe then they will know its not right. Maybe your not doing a full conditional inspection or just have they cowling off to fix a minor issue. How many people put a hand on every fitting everytime they have the cowling off? That's the time when a visual indicator could tip you off to something amiss. Torque Seal does have its place and I do place it above diddly, but I do understand what Walt's saying, and I'm sure we're more or less on the same page. I was just a little let down by the harshness. No harm no foul.
 
I think the REAL lesson here is that any time the cowling is off, do a good look over inspection to see if anything is out of sorts. Pierre Smith did that last year after an inflight alternator failure, and the cowling was off during that repair. Probalby saved his life as well as his wifes' and anyone else that may have flown with him. Not the alternator failure-----the fuel hose laying on the exhaust. Walt's SOP to put a wrench on B nuts is great advise--only takes a few minutes during an oil change. ( what do you do while its draining?)
Torque seal is a good visual, but nothing compares with the good ole wrench check. I dont have an RV, or a plane, but I fly quite a bit with friends that do. Its the little things that count.
My .02 cents
 
The cowling was probably off at least three times. After test flight and two oil changes. Every fitting and many bolts on my plane have torque stripe. I went through three or four tubes. It does tell me that I torqued it. Since I did not have Army QC available like I did 20 yrs ago, I put my QC hat on and rechecked all torques before first flight. I will continue to recheck anytime a particular area is opened up.

Another good reason to have fuel flow indication and some test data sheets at various temps/altitudes/power settings on board at all times. If something looks off, you are better off hitting the nrst button and check it, even if only one hour from your destination. It only takes a few minutes and fire can be coming through the floor(this happened recently to a good friend). No custom paint necessary at that point. I am also glad I installed my 250F cowl exit temp limit switch. Good job Walt!
 
Yes, but the part about torque seal meaning diddly kindda rubs me the wrong way and I think Walt could have been a little clearer in his meaning.

What I should have said was: when it comes to inspecting experimental aircraft, I don't accept torque seal as proof of proper torque, I check it regardless.

I may not necessarily put a wrench on every fitting on my own aircraft at every old change because I have a high confidence factor in my own work (but I will at ever condition insp).

When it comes to working on other folks aircraft, I leave nothing to the imagination (thats why an annual condition inspection with me costs a little more than the "other" guy).
 
Man, there's a fair amount of thread drift here. Bottom line for me: How the heck does some of this stuff pass inspection?

I would think someone using a nylon tie as a firesleeve clamp would scream., "stop whatever else you're doing and take a good LONG look at everything on this engine."
 
How often does a properly torqued fuel line fitting come loose?

I agree with the idea of checking all critical fittings early and often with a newly built aircraft and whenever the cowl is off after that.
 
I hate to be a pain, but a 302* high temp nylon tie wrap wasnt exactly what I had in mind. We all have seen firesleeve secured by safety wire, which is better than nothing. Fastenal makes a stainless pinch band that can work too, for those doing a one time assembly.
 
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Ref Fuel leak

I had to off field a Commanche 260 on 10/2/1992 in Aliceville AL (N8548P)
for NTSB reference for EXACTLY the same reason. Luckily the three of us walked away thanks to good primary off field emergency proceedure training during my primary flight training (thanks Don Lindsay).;)
 
The truly amazing thing for me is how well designed our aircraft fittings are. There should have been lots of warning that this fitting was leaking.
I am surprised that the smell of fuel, or a stain did not get noticed early on, before the leak became so gross. No disrespect intended.
I recently had a pin hole leak in a hard fuel line on the Bucker caused by some internal corrossion due to a poorly fabricated part. The amount of fuel leaking was barely enought to cause a drip, yet I could smell the fuel immediatly when I flew it, and this is an open cockpit.
 
Man, there's a fair amount of thread drift here. Bottom line for me: How the heck does some of this stuff pass inspection?

I would think someone using a nylon tie as a firesleeve clamp would scream., "stop whatever else you're doing and take a good LONG look at everything on this engine."

It is all related, we are learning and being nice.

As far as passing inspection...the builder has to make the signoff before first flight, so he is ultimately responsible. It depends on who you get to look at your plane. DAR/A&P's may notice. The FSDO inspector may not. I would think neither check torques on all hardware/fittings and they won't be with you on your test flights.
 
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The truly amazing thing for me is how well designed our aircraft fittings are. There should have been lots of warning that this fitting was leaking.
I am surprised that the smell of fuel, or a stain did not get noticed early on, before the leak became so gross. No disrespect intended.
I recently had a pin hole leak in a hard fuel line on the Bucker caused by some internal corrossion due to a poorly fabricated part. The amount of fuel leaking was barely enought to cause a drip, yet I could smell the fuel immediatly when I flew it, and this is an open cockpit.

The only time pressure is on that line on the ground is with the boost pump on, throttle and mixture forward(priming). Only about an ounce of fuel at low pressure flows through. At this point in the start procedure one may just think they overprimed. We don't leak test this during our before test flight checks. I only tested to fuel servo outlet while doing my 42 gph fuel flow test.

After start up and in flight there is alot of heat and airflow to dilute the 2 oz of fuel leaking every minute. Depending on firewall sealing, eyeball vent
open/closed position and your sense of smell it may not be noticed. These lines can stay snug enough to not leak measureably for hours, but once they
do turn it can turn in to a gusher in a short amount of time depending on line position/tension/pressure and vibration frequency.

I had a one drip leak every five minutes during pre-test flight checks just after fuel filter in tunnel with boost pump running. I thought it was my neighbors leaky Mooney. I finally pinpointed it with an electronic combustible gas detector.
 
Easy fix-Safety wire

I am thinking all these critical B-nuts, especially on the fuel system, should be safety wired. may be a pain in the but, but this pain is better than a fire. JMHO
 
Johnny---there are alot of place that you would have to be a magician to safety the nuts. Safetying isnt the answer, but checking the connections is.
 
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