LET Blanik L-13 OE-0935 History Details?

[Tim Taylor]

Does anyone have a source for the flight history of Blanik L-13
OE-0935 that was involved in the wing failure? Total hours, take-off/
landings, aerobatics, and winch launch history?

[Andy[_1_]]

On Aug 30, 12:48*pm, Tim Taylor > wrote:
> Does anyone have a source for the flight history of Blanik L-13
> OE-0935 that was involved in the wing failure? *Total hours, take-off/
> landings, aerobatics, and winch launch history?

If you're going that route you'll probably need all accident and
repair history as well.

Andy

[Andrew Corrigan]

It would be interesting to know this information for curiosity sake.

But, I'm not sure if this historical data can conclusively say fatigue
was the root cause of the failure. The failure might have been caused by
flying the glider out of it's design limits.

This would not be hard to do if a pilot screwed up an aerobatic manevour.
If things go wrong, Vne and G limits can be easily exceeded in a hurry.

Our friends that had the last flight may done a normal basic training
flight. But, a previous flight might have damaged the glider.
Unfortunately, no one said anything about over stressing the glider and
someone else paid the price.

Andrew


At 20:12 30 August 2010, Andy wrote:
>On Aug 30, 12:48=A0pm, Tim Taylor wrote:
>> Does anyone have a source for the flight history of Blanik L-13
>> OE-0935 that was involved in the wing failure? =A0Total hours,
take-off/
>> landings, aerobatics, and winch launch history?
>
>If you're going that route you'll probably need all accident and
>repair history as well.
>
>Andy
>

[vaughn[_3_]]

"Andrew Corrigan" > wrote in message
...
> Our friends that had the last flight may done a normal basic training
> flight. But, a previous flight might have damaged the glider.
> Unfortunately, no one said anything about over stressing the glider and
> someone else paid the price.

I think that accident investigators can fairly positively tell the difference
between a structure that has failed from overstressing and one that has failed
from fatigue. The AD says "The preliminary investigation has revealed that the
fracture may have been due to fatigue". So there seems to be little reason to
suspect this accident resulted from prior overstress damage; particularly damage
from a recent flight.

Vaughn

..

[Bart[_4_]]

On Aug 30, 2:42*pm, "vaughn" > wrote:
> I think that accident investigators can fairly positively tell the difference
> between a structure that has failed from overstressing and one that has failed
> from fatigue. *The AD says "The preliminary investigation has revealed that the
> fracture may have been due to fatigue". *So there seems to be little reason to
> suspect this accident resulted from prior overstress damage; particularly damage
> from a recent flight.

If a glider is routinely overstressed by, say, 20%, I would not expect
it to fail. I would, however, expect its fatigue life to be
significantly decreased. Years later, the wing could fail when under
"normal" load, and the fracture would look like a fatigue fracture. I
may be wrong... am I?

Bart

[Bart[_4_]]

> If a glider is routinely overstressed by, say, 20%...

I would like to add that the scenario above is purely theoretical and
I am not trying to suggest that the accident in Austria was caused by
anyone who has flown the glider in question in the past.

B.

[[email protected]]

Let's not speculate too much. This is not as simple it appears IMO.

I was on the phone with the FAA Engineer this AM. He has a difficult
problem on his hands, and the MFG is not being helpful. We need to
ping the Mfg via Vitek, and the SSA to get on board with this problem.

Accident aicraft had been overhauled in the past, recent annual, and
only 2318 hrs.

I urge you all to look at the overhaul manual, and understand the
structure and fatigue concerns, there is a lot of info there.

MM.

[Andrew Corrigan]

Bart,

Thank you for being sensitive to our friends in Austria. Our problems with
the L-13’s are nothing compared to the issues the families of the pilots
have.

You asked about the effect of exceeding limits. Your logic is correct.
Ductile metals, such as aluminum, have known performances. Stress-Strain
data is what engineers use to design structural components. It will tell
them the Elastic Limits, Elongation Limits, Ultimate Tensile Strength, and
when a Fracture will occur.

Your comment of a “Theoretical” scenario of constantly flying 20% above
the limit might result in a reduced life of the spare.

My “Theoretical” scenario would be one flight where the pilot got into
trouble and accidentally exceeded 50%. This would take the spare past it
Elastic Limits and significantly reduce it’s life. To add to my scenario,
if the limits were exceeded 10-20 years ago, the oxidization build up on
the aluminum might mask that damage. A fresh fracture would be shiny
because of the absence of oxidation.

Again, this is a theory that has almost no data backing it. However,
there are approximately 3000 Blaniks in the world that have been flying
for 2-3 decades. That is a solid record that speaks to the design life.
The L-13 in question is low time and had been over hauled. It does not
appear to be the norm.

Since this is a fatality, the investigators will get to the root cause for
the accident. They will probably review the design calculations. They
might also do a metallurgic test to determine the pedigree of the aluminum
in the spare. Their investigation will take time. We probably won’t see a
report for a year. (Again, my guess)

Andrew




At 22:21 30 August 2010, Bart wrote:
>> If a glider is routinely overstressed by, say, 20%...
>
>I would like to add that the scenario above is purely theoretical and
>I am not trying to suggest that the accident in Austria was caused by
>anyone who has flown the glider in question in the past.
>
>B.
>

[jcarlyle]

Andrew, there would be no masking due to oxidation. Anyone who has
ever looked under a microscope at a fatigue crack scenario leading to
overload failure would agree with Vaughn above, who said "accident
investigators can fairly positively tell the difference between a
structure that has failed from overstressing and one that has failed
from fatigue." Believe me, if this failure had fatigue as its initial
cause, the evidence will be very clear - the fatigue "bench marks"
won't disappear. An overload due to high Gs that blunted the fatigue
crack temporarily will also be evident.

-John


On Aug 31, 10:12 am, Andrew Corrigan >
wrote:
> if the limits were exceeded 10-20 years ago, the oxidization build up on
> the aluminum might mask that damage. A fresh fracture would be shiny
> because of the absence of oxidation.

[Andrew Corrigan]

John,

My intent is to keep an open mind on the root cause of the failure.
Prematurely stating this is fatigue issue is a mistake.

The investigation will have to look at many aspects. How was the glider
used or abused? It might include metallurgic analysis to ensure the
aluminum spare was made from the correct type of alloy, tempered properly,
and has no inclusions, etc.

As a person that has looked through a microscope at granular structure of
metal I can tell you this. This is not a lab experiment where all the
variables are controlled. There will be a lot of unknowns because of the
age of the glider, how it was flown, and how it was cared for. As such,
this is not a text book case where engineers can pull out a chart and look
up data to determine a resultant.

As an aerobatic pilot, I can tell you this. We make mistakes. If trained
properly a pilot will be able to recover from any situation without
exceeding the glider’s limits. However, inverted recoveries are not
intuitive. A simple mistake while inverted can quickly lead to the glider
going over Vne or exceeding G limits. It’s easy to do. Something happens;
the pilot gets caught off guard, takes a few seconds to figure things out,
mean while the glider is accelerating towards the ground. If inverted,
pulling on the stick will cause the glider to accelerate. The pilot may
never have known the ASI was above Vne. I’m not saying this happened to
the glider in question.

What I am saying is this “Don’t label the root cause as fatigue until the
investigators have done their due diligence and reached a conclusion based
on ALL the data!”. Labelling the issue as fatigue without data is not just
when there are thousands of these gliders with tens of thousand hours
without failures.

Andrew



At 14:44 31 August 2010, jcarlyle wrote:
>Andrew, there would be no masking due to oxidation. Anyone who has
>ever looked under a microscope at a fatigue crack scenario leading to
>overload failure would agree with Vaughn above, who said "accident
>investigators can fairly positively tell the difference between a
>structure that has failed from overstressing and one that has failed
>from fatigue." Believe me, if this failure had fatigue as its initial
>cause, the evidence will be very clear - the fatigue "bench marks"
>won't disappear. An overload due to high Gs that blunted the fatigue
>crack temporarily will also be evident.
>
>-John
>
>
>On Aug 31, 10:12 am, Andrew Corrigan
>wrote:
>> if the limits were exceeded 10-20 years ago, the oxidization build up
on
>> the aluminum might mask that damage. A fresh fracture would be shiny
>> because of the absence of oxidation.
>

[Canav8]

Update on Blanik ADs and Manfacturer Bulletins
> 8-31-2010
>
> The continuing airworthiness issues, manufacturer’s (LET / Aircraft
> Industries) Mandatory Bulletins, European Aviation Safety Administration
> (EASA) Airworthiness Directives and the Federal Aviation Administration
> (FAA) ADs concern SSA as well as the owners and operators of the affected
> L-13 and L-13A Blaniks. It is likely that most of the Blanik fleet in the
> United States and around the world will be affected and/or grounded before
> the manufacturer and the European agencies issue appropriate methods to
> inspect and modify the aircraft to prevent recurrence of the problems that
> have led to structural failure and death. The SSA has worked with FAA
> since the beginning of the current spar problems.
>
> At this point the manufacturer and EASA have not developed or approved an
> effective inspection or modification program to ensure safe continued
> flight of the affected aircraft.
>
> However, the FAA’s latest AD states that the flight-hour record-keeping
> requirements of the manufacturer do not apply to American operators and
> that the FAA will review Alternative Methods of Compliance (AMOC’s)
> presented to them. These statements are encouraging for American
> operators.
>
> SSA does not have the expertise to engineer solutions, but some of our
> members may. SSA encourages qualified members who work on aircraft
> inspection and repair methods to contact Greg Davison, Aerospace Engineer
> at FAA’s Small Airplane Directorate in Kansas City at (816) 329-4130.
> Also please send copies of correspondence with the FAA to SSA and we will
> summarize and publish information about them on this site on a regular
> basis.
>
> SSA will also use this page to publish other written reports of
> developments or offers of assistance. In particular, FAA is working on an
> informational statement that it hopes to forward to SSA for publication
> in the next few days. At the moment SSA believes that acting as an
> information clearinghouse is its most appropriate course of action while
> it encourages its members and the owners/operators of Blaniks to work
> together to develop technical solutions.
>
> Finally, SSA also believes that owners and operators of affected Blaniks
> should make the manufacturer (LET / Aircraft Industries) and its American
> representative (Blanik America) aware of their concerns and the need for
> their help and timely solutions. Meanwhile, owners with valid questions
> and suggestions continue to be invited to contact the FAA as stated in
> the AD’s.
>
> SSA Aircraft Certification Committee
>
> Posted: 8/31/2010 By: Government Liaison Committee

[No Name]

Many years (and brain cells) ago I recall looking at an old L-13
spar end cap and it had a very large number of bolts going through
it. It seemed like it was very close to what I remember as a hole
to edge and hole to hole distance requirement. My calibrated
thumb nail showed it to be within what I remember as a 2D
distance but I remember that from rivet holes to edge on wing
skins. I wonder if some of this is caused by hole to hole to edge or
radius cracks and if so that would be a very serious concern. Also,
I believe that the 2D used to be 1.5D and there had been questions
if that was hole edge to edge or hole center to edge.