"Steve R." wrote in message
...
"Stu Fields" wrote in message
...
It seems that if there are two possible causes for a helicopter accident,
the preferred one for the manufacturer is the one for which they have no
fault. That certainly is the best for them. However, lets say that a
low hour helicopter suffers a failure directly attibutable to fatigue.
Further lets assume that the helicopter had had a prior series of hard
landings or other beyond normal stress loadings. Now lets further assume
that the fatigue failure occurred at a point in the helicopter drive
system where a diameter change was machined into the shaft without any
radius or attempt at a proper fillet which yielded a strong stress riser.
Lets say that the kit manufacturer is very aware that a number of kits
have been sold with the same machining flaw.
Should the kit manufacturer issue a service advisory statement advising
all owners of those ships of a potential safety issue caused by those
parts? What should their action be? Recall and supply exchange parts for
no charge? Recall and supply exchange parts for their cost? Change the
machining process and ignore the other parts out there?
How about sell the business to someone else and just duck and hope that
nothing bad ever comes from the above?


Hi Stu,

You mention a lot of variables here. My thoughts are this - first, why
did the bird have a series of hard landings or other "beyond normal stress
loadings?" Those, to me, sound like a piloting issue and not necessarily
the kit manufacturers problem. Second, if the kit manufacturer discovers
that they're selling parts that do have some kind of defect in design or
machining, I think they should be obligated to making that right, either
by an outright recall or by offering proper replacements to kit owners at
cost. At the very least, they should issue a service advisory statement on
the problem to be certain that the kit owners are aware it.

Having said that, we are talking about "experimental" aircraft here. If I
understand all that correctly, that means the owner/builder "is" the
manufacturer of the aircraft and is ultimately the one responsible for the
safe operation and maintenance of said aircraft. Still, if the kit
manufacturer has any integrity, they'll be doing all they can to assist
their customers with parts and materials that are discovered to be less
than ideal for the job it's asked to do.

I'm reminded of something Air Command did many years ago when they finally
came around to the benefits of an in-line thrust design for pusher style
gyroplanes. If I'm remembering correctly, they issued a statement
advising anyone owning the older/original design bird to stop flying them
and offered a new frame upgrade with a center line thrust design to "any"
owner, "at cost," regardless of whether those owners bought the bird
directly from Air Command or from an individual. I think it took a lot of
guts for them to do that and speaks volumes for the integrity of the
company.

Does that answer your question? At least it might help spark the
conversation! :-)

Fly Safe,
Steve R.


Surprising enough a series of hard landings were experienced by high time
helicopter pilot. Ship didn't have anywhere near 400hrs when a shaft in the
transmission experienced a fatigue failure. The focus was on the hard
landings as the cause and the stress risers of the shaft were ignored.
Another accident occurred where the builder did something not right which
caused some strong vibrations. He corrected the problem but didn't replace
a part that had a near zero radius fillet and that is exactly where the
fatigue failure occurred. This resulted in a fatal accident. Another fatal
accident occurred where another fatigue failure occurred at a place where
the fillet radius was reported as sharp. Again other historical occurences
were logged and the failure occurred at the sharp fillet radius. Again the
focus was placed on the historical occurrences and not on the poorly
machined fillet.
There are a number of kits out there that have been supplied similar
elements. The machinist for these parts had drawings which did not call out
a fillet radius. (That has been changed now.)
Another instance was called to the kit manufacturers attention where a
rubber seal was scarring (0.020 deep jagged groove) in a main rotor shaft.
The response was that they had seen this before and it didn't constitute a
dangerous condition.
To date the kit manufacturer has not sent out any warnings. They merely, on
their website, offer to inspect and replace the parts if you are concerned
about them. It sounds like they don't see a problem, but if you the
builder-flyer does, they will try to make you happy.
All of these parts are enclosed inside elements that come from the kit
manufacturer complete and closed up and evern cotter keyed. Unless the kit
builder tears these elements down and has enough of a technical background
to do a good inspection, he will not be aware of the risk that he is taking.
Yeah the Air Command story speaks highly of someone's integrity. (We
probably know the guy). The "Center Line Thrust" was an arguable issue.
Cdr. Ken Wallis had his opinions about this and he had more than a few hours
in non "Center Line Thrust" ships. On the other hand the Stress
concentrations seen in this other kit is a well known issue to avoid.
Yeah I wish this kit manufacturer of issue would adopt the Air Command
philosphy.

Stu