L13 Blanik Mandatory Bulletin

After a fatal accident in Austria LET issued a Mandatory Bulletin:
http://www.let.cz/files/bulletines/M...9a_english.pdf

EASA issued an Emergency Airworthiness Directive:
http://www.caa.co.uk/docs/33/easa_ad_2010_0119_E.pdf

On Jun 22, 7:50*pm, Ernst wrote:
After a fatal accident in Austria LET issued a Mandatory Bulletin:http://www.let.cz/files/bulletines/M...9a_english.pdf

EASA issued an Emergency Airworthiness Directive:http://www.caa.co.uk/docs/33/easa_ad_2010_0119_E.pdf

Does anyone know if the L23 could have similar problem?

Reading the MB, It appears that based on the "flight data" of the aircraft,
and high number of launches per flight hour, the concern is overstressing
from repeated winch launches. LET is requesting all users submit flight
statistics for further evaluation plus a one time inspection of the load
bearing aft spar cap in the fuselage carry through structure.

I do not know if the L-23 and the L-13 have the same construction for the
aft spar cap.

"Ernst" wrote in message
...
After a fatal accident in Austria LET issued a Mandatory Bulletin:
http://www.let.cz/files/bulletines/M...9a_english.pdf

EASA issued an Emergency Airworthiness Directive:
http://www.caa.co.uk/docs/33/easa_ad_2010_0119_E.pdf

Provided that the correct weak link is always used, it should not be
easily possible to damage a glider by winch launching it. What
aerobatics had this glider done?

Derek C


On Jun 23, 3:23*am, "BT" wrote:
Reading the MB, It appears that based on the "flight data" of the aircraft,
and high number of launches per flight hour, the concern is overstressing
from repeated winch launches. LET is requesting all users submit flight
statistics for further evaluation plus a one time inspection of the load
bearing aft spar cap in the fuselage carry through structure.

I do not know if the L-23 and the L-13 have the same construction for the
aft spar cap.

"Ernst" wrote in message

...



After a fatal accident in Austria LET issued a Mandatory Bulletin:
http://www.let.cz/files/bulletines/M...9a_english.pdf

EASA issued an Emergency Airworthiness Directive:
http://www.caa.co.uk/docs/33/easa_ad_2010_0119_E.pdf- Hide quoted text -

- Show quoted text -

Am 23.06.10 04:23, schrieb BT:
Reading the MB, It appears that based on the "flight data" of the
aircraft, and high number of launches per flight hour, the concern is
overstressing from repeated winch launches. LET is requesting all users

Sigh. The urban legend lives.

On Jun 23, 6:58*am, John Smith wrote:
Am 23.06.10 04:23, schrieb BT:

Reading the MB, It appears that based on the "flight data" of the
aircraft, and high number of launches per flight hour, the concern is
overstressing from repeated winch launches. LET is requesting all users

Sigh. The urban legend lives.

Can you please clarify that remark? I don't see any urban legendry
here.

Winch launching inherently load the wings in bending more than
aerotow. Maybe not enough to actually exceed the design load of the
wings. But certainly enough to contribute a substantial amount of
fatigue and to make a measurable difference in long-term service
life.

When fatigue has weakened a structure, and then you apply a load that
exceeds the diminished capacity of that structure, it will fail. You
can say that it was overstressed, or you can say that it wasn't
overstressed and that it just exhibited a fatigue failure. Whatever
you call it, you still have a broken structure.

Thanks, Bob K.

Bob Kuykendall wrote:
Can you please clarify that remark? I don't see any urban legendry
here.

Winch launching inherently load the wings in bending more than
aerotow. Maybe not enough to actually exceed the design load of the
wings. But certainly enough to contribute a substantial amount of

Provided the correct weak link is used, the wing load during a winch
launch never exceeds 2g. Each turbulence stresses the structure more
than that. But as I've already said: Urban legends are here to stay.

On Jun 23, 3:58*pm, John Smith wrote:
Bob Kuykendall wrote:
Can you please clarify that remark? I don't see any urban legendry
here.

Winch launching inherently load the wings in bending more than
aerotow. Maybe not enough to actually exceed the design load of the
wings. But certainly enough to contribute a substantial amount of

Provided the correct weak link is used, the wing load during a winch
launch never exceeds 2g. Each turbulence stresses the structure more
than that. But as I've already said: Urban legends are here to stay.

Actually the maximum bending load on the wingspar during a winch is
equivalent to about 3 g, due to the point loading on the fuselage and
the lack of g unloading on the wings, but that still shouldn't cause a
failure. I have looked at the newspaper reports on this accident, but
they don't state which phase of flight the glider was in when it broke
up. They say that it crashed into a forest, which sounds as though it
was in free flight, rather on a winch launch when it would have been
over the airfield. Does anyone have any better information?

Derek C

Derek C wrote:
failure. I have looked at the newspaper reports on this accident, but
they don't state which phase of flight the glider was in when it broke

To my knowledge, the Blanik was aerotowed to about 1200m AGL, from where
an aerobatics program was flown. The wing broke only after the
aerobatics had been finished. It was too low for the two pilots to bail out.

On Jun 23, 8:17*am, Derek C wrote:

Actually the maximum bending load on the wingspar during a winch is
equivalent to about 3 g, due to the point loading on the fuselage and
the lack of g unloading on the wings, but that still shouldn't cause a
failure...

I think that 3g equivalent load is a large enough percentage of the
limit load to constitute a fatigue concern. If I were assessing
service histories, I would definitely want to know the cycle count on
activities likely to cause that kind of load.

Thanks, Bob K.