B-nut Fire Safety

[CFI1513840]

I just read about an incident involving a fire in an RV-8. Fortunately, it happened on the ground and both occupants were able to exit the aircraft safely. The fire was extinguished in a timely manner by ground personnel. The problem was traced to a loose B-nut at the firewall.

This brings up the point of safetying B-nuts. Obviously, Vans thought it was necessary for the fuel tank pickup tube and issued a Service Letter, but what about all the other B-nuts?

Are there some special circumstances that make only the fuel pickup tube prone to loosening? Why not safety all B-nuts? Would loctite be a possible solution? I realize that there are thousands of airplanes flying around with unsafetyed B-nuts, but knowing that fact would be little consolation if your airplane is on fire.

[Vern]

My dad and I rescued a member of the US Aerobatic team (Bob Nance) many years ago when the fuel line b-nut loosened and caught his Great Lakes Special on fire after landing. He stomped on the brakes and flipped [yes-even taildraggers can flip. This was NOT an A model} The the plane had just had an engine overhaul.

I once met a missionary mechanic who was was interrupted while re-installing a fuel line. When he returned to the job, a visual did not reveal the loose nut. He later watched the departure takeoff and saw the plane catch fire and crash.

[az_gila]

Originally Posted by Vern

My dad and I rescued a member of the US Aerobatic team (Bob Nance) many years ago when the fuel line b-nut loosened and caught his Great Lakes Special on fire after landing. He stomped on the brakes and flipped [yes-even taildraggers can flip. This was NOT an A model} The the plane had just had an engine overhaul.

I once met a missionary mechanic who was was interrupted while re-installing a fuel line. When he returned to the job, a visual did not reveal the loose nut. He later watched the departure takeoff and saw the plane catch fire and crash.

...good $1.95 safety item!

http://www.skygeek.com/f-900torque-seal-orange-.html

[CFI1513840]

It may be just a question of strength, but from what I understand, torque seal does not "lock" the part in place, but rather provides an indicator that will show if the part has loosened. In other words, a visual inspection would still be required to detect a loosened nut. What I had in mind was a something more like locktite or pro-seal that would positively keep the nut from coming undone.

[Mel]

I think Gil's point was that if the missionary mechanic had been in the practice of using torque seal, he would have noticed that the b-nut had not been final tightened.

[AlexPeterson]

Originally Posted by Mel

I think Gil's point was that if the missionary mechanic had been in the practice of using torque seal, he would have noticed that the b-nut had not been final tightened.

This is sort of a mystery to me - why many don't use the inspection lacquer, that is. I am amazed at how many "ready to fly" planes I've looked at that don't have inspection lacquer telling the story of the individual nut's tightening. Another issue are those that tighten ten nuts, then apply the inspection lacquer to all ten. Defeats the purpose. Torque one, mark one, repeat as necessary.

Oh, and I have found more than one loose b-nut on said planes. One loose nut could kill you, why not add 20 minutes' time to the airplane assembly by doing this procedure correctly?

[rocketbob]

Originally Posted by AlexPeterson

This is sort of a mystery to me - why many don't use the inspection lacquer, that is.

Last year I made up a few lines on the Mustang I help a friend of mine with. When you have as many lines as these:



Its not uncommon to tighten something up thinking you're done then have to take it apart later. Then you have to clean off the old torque seal and redo it. That can be a major pain. When plumbing the sequence valves here in order to get one line off it often took getting two or three others off to get to it. The other gear well was worse.

Or, you tighten something up, look down for the torque seal, and you end up marking the wrong one. Easy to do if you get distracted.

So I have a simple rule. If you put it on, you tighten it. If you leave it loose, either leave them ALL loose or tag them as I did here with masking tape. When something's tight, pull the tape off. And I always double check every nut before I call anything finished, especially on b-nuts.

[deene]

It still scares me to relate this story...

Many years ago, I flew my former homebuilt after an installation of a new fuel pressure gage. As I climbed out, a strong fuel order was evident. I Immediately reduced power and landed. I rolled to a stop near the pumps and pulled the mixture leaving all other switches alone. Opened both doors and evacuated the plane.

After an hour or so of ventilation, I pulled the plane to my hangar and looked for the problem...a loose b-nut on the fuel pressure line at the firewall bulkhead, aft.

The whole bottom of the fuse was soaked with fuel and any ignition source would have set off an conflaguration which would have mean't a short end to me and my plane.

So, on my new project, all torqued fasteners and components have a torque seal mark...any not marked will be fixed before first flight.

[N814P]

OK - I'm a beginning builder and have a question. By "B Nut" are you referring to (in the above posted picture) the blue colored nuts that hold the fuel lines to the different T fittings? I'm only on the empennage kit, but do Van's instructions call for any kind of seal on the outside, or is it just common A&P knowledge?

There's a community college about 20 miles from my home that offers an A&P certificate class -- I may just figure that into the cost of the build, just to be safe

[CFI1513840]

Originally Posted by N814P

OK - I'm a beginning builder and have a question. By "B Nut" are you referring to (in the above posted picture) the blue colored nuts that hold the fuel lines to the different T fittings? I'm only on the empennage kit, but do Van's instructions call for any kind of seal on the outside, or is it just common A&P knowledge?

There's a community college about 20 miles from my home that offers an A&P certificate class -- I may just figure that into the cost of the build, just to be safe

Ralph,

Yes, the B nuts are the blue colored nuts that are used on the fuel lines. A couple of years ago Vans issued a service letter to safety the B nuts on the fuel tank pickup tubes with safety wire. Apparently there were some cases of fuel tubes coming loose. You'll become familiar with this mod when you do the tanks. Otherwise, there is no requirement that I know about, either on homebuilt or certified aircraft, to safety B nuts. They are simply tightened, which is why I asked the question in the first place.