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Injector Line Failure In Flight

Toobuilder

Toobuilder

Well Known Member
Took a very short hop this am with my bride to check out the results of a small local brushfire. Cruising sedately along at 22 squared and lean we approached our airport for landing. Still out about 2 miles, the engine went rough and #4 EGT dropped out on the way to ambient temp. In light of the recent ignition issues I have been though, that was my first thought. Quick mag check showed exactly the same behavior on both ignitions, so that ruled out spark as the issue. That only leaves fuel and air... Since the other cylinders are still going strong, "air" seems unlikely as a cause. So that leaves fuel. With fuel injection and all other indications normal, a blocked nozzle pops into my mind - not a huge deal...

...Then I smell the raw fuel! I'm suddenly not interested in troubleshooting any more and just want on the ground ASAP. Fortunately, I'm on top of the pattern and simply chop the power, bleed off some speed with some s turns and set myself up for an uneventful landing.

Minutes later I have the cowl off and sure enough, #4 injector line is broken right at the nozzle and dumping fuel right on cylinder head near the spark plug boot. Good thing I didn't go full rich! Anyway, it's an odd failure in the respect that the line broke INSIDE the nozzle ferrule and the silver solder separated cleanly at the joint. Hard to inspect for THAT failure mode!

All in all it was a non event, but I thank God this this didn't happen at 8500 feet over the open desert!

29mwsw8.jpg
 
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Yikes!

Amazing that you didn't get a fire!
I did a repair on a line like this for a Maule one time.

It was clear to me that the silver-braze job was not done right. Lots of folks don't know how to braze stainless steel properly.

I used to build custom bike frames, so I'm pretty good at silver brazing:rolleyes:
 
Inspect those injector nozzle lines!

Actually we see this type of pending failure a lot. Most people and mechanics kind of forget about the nozzle lines. But being that these systems have thousands of hours on them most people don?t think about replacing the nozzle lines on their engines at the time of the overhaul of the components. Even if installed correctly the metal will work harden at the radius going down to the nozzle line cone (ferrule). If you inspect this area around the braze joint (use a 5X to 10X magnification glass) and you find cracking of the braze material next to the nozzle line material, it?s time to replace the lines. Personally I would replace the lines at engine overhaul (2000 hours), for what it costs (around $110 for a four cylinder engine) it?s cheap insurance. Another issue with old lines is the coking up of the interior of the line with fuel dye. After repeated heat cycling of the lines on top of the engine, the fuel dye will no longer dissolve and will build up on the inside of the nozzle line. This debris then breaks off and can clog the injector nozzle. The material will look like black hard substance that will crumble if you can get a piece of it. Again, this doesn?t happen until the lines have thousands of hours on them. But you would be surprised how many of these we see that are probably from the 1960?s.

So next oil change, check you injector nozzle lines and the clamps for proper installation and condition of the rubber on the clamps (it?s good practice to do it every oil change or at condition inspection). We make nozzle lines and can supply the clamp kits that comply with the Lycoming Service Bulletin.

Don
 
These certainly look to be OEM lines, and though appear to be in good overall condition, are likely to be as old as the basic engine.

Don, I'll be contacting you soon.
 
Amazing that you didn't get a fire!
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That's what I used to/still sorta think. But, after finding a half dozen of these broken here and there, and worse yet seeing a couple engines encased in blue paste from long term leaks I'm stumped. I'm stumped as to why they don't all ignite, they don't though.
 
Auto Ignition

aerhed said:
That's what I used to/still sorta think. But, after finding a half dozen of these broken here and there, and worse yet seeing a couple engines encased in blue paste from long term leaks I'm stumped. I'm stumped as to why they don't all ignite, they don't though.
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You need about 475 deg F. to auto ignite gas so the cyl-heads will not be enough alone to get it started.

The Exhaust temp. is enough though:eek::eek::eek: If you spray gas straight onto the exhaust riser you WILL have a fire.
 
I am guessing with 200-350F cylinder heads and all of that dilution air, any liquid has turned to vapor and too lean to ignite by the time it reaches the hot exhaust pipes. It amazes me too.

Glad all worked out for you guys.
 
That line looks like it had been under a fair amount of stress.

Shaping them so they sit in position might help.

Maybe Don can expand on that.
 
RV10inOz said:
That line looks like it had been under a fair amount of stress...
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Nope, not so much. The clamp is mid span, and several inches away, so there is only the slightest pressure needed to pull the free end back to the injector. I am aware and in full agreement that hard lines should not be pulled into alignment by force. That's aircraft mechanic 101 stuff, and I learned that as a much younger man.
 
OK, just looked like it had sprung back a fair way when it broke. Maybe that was you when you found it.

For the newbie's watching, this is a great thread!
 
Spin up an old thread....

One week to OSH, so I spent some time yesterday inspecting inside the engine compartment.

Well, well, lookie here:



A clean separation at the braze/ferrule joint is obvious, at only 581 hours. And yes, it was correctly fixated with the proper Adels in the proper places, and there was no residual stress as installed.

However, I think there are two separations here. Note where the fuel stain was collecting on the tube in the first photo....above the brazed area. It appears that fuel was leaking at the small diameter where the braze meets the tube. Note that some of the braze material seems to have flaked away.

There was a possible clue in operation. Recent EGT indications said this cylinder was drifting leaner than previous. It was slight, but noticeable; it was no longer peaking close to the others.

 
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Is Teflon an option

Would flexible fuel lines like the ones that TS Flightlines make work in this area?
 
Happened to a friend with fatal results

A friend of mine in the late 90's broke a injector line in a HR2. An in flight fire ensued. As I remember there was an aluminum plate (definitly a no no) covering a hole in the firewall. The fire quickly burnt through the a aluminum. He was able to land the plane and save his passenger. He died two weeks later from breathing super heated air.

Steve
 
DanH said:
Spin up an old thread....

One week to OSH, so I spent some time yesterday inspecting inside the engine compartment.

Well, well, lookie here:
Click to expand...

So glad you found this before blasting off to Osh!

I know you love to fire test stuff and I know you most likely have one of the most fire resistant firewalls in RV land but I am sure glad you did not get to experience a real test on that plane!
 
Considering how durable these lines are in actual operation, a failure at 581 hrs is borderline infant mortality.

At any rate, much better to find it in hangar than on the conga line into OSH!
 
grubbat said:
Would flexible fuel lines like the ones that TS Flightlines make work in this area?
Click to expand...

I don't think so -- these are the injector lines from the divider (aka spider) to the injector nozzles and the diameter is pretty small. I just did this SB as part of my 1st condition inspection last month.
 
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