This is a repository of information regarding the Blanik L13 spar issue.  Similar documentation can be found on Wikipedia, and at SSA (login required).  This website has a USA bias.

See the Files page for all the documents.

The website was last updated on 22 April 2015.  Send comments here.

Latest Updates
22 April 2015 - Information about Blanik Aircraft CZ added.
05 February 2013 Mandatory Service Bulletin L13/116a added.
26 February 2012 - FAA section updated with news about a statement released to SSA.
21 July - added the "Current Airworthiness" synopsis.
21 July - LET MB L13-112a and EASA AD 2011-0135 added to Files section.
6 July - BGA Technical Note cited.
20 June - EASA AMOC 10035384 added.
15 June - EASA STC 10035295 added.
24 May - Update from LET added.
24 May - Added reference to Blanix. 
18 April - Added updated customer information and an an order form for the STC from AD&C.
25 March - Update from LET added.
28 February - L13 A1 gliders returned to flying status
27 February - Czech presentation added to Files section.  Seeking a translation. Email if you can help, thanks.
24 February - Rind email added.
25 January - Robertson opinion paper added.
6 January 2011 - added status report from LET Product Support Department.
28 December - corrected a statement about the validity of EASA ADs in Australia.
31 October - Undated letter from SSA to LET added.
5 October - Information regarding the grounding of gliders in Australia and New Zealand added.
5 October - Official English version of LET opinion paper added, unofficial version removed.
30 September - LET opinion paper added.
23 September - Llewellyn Modification: factual information added, speculation removed
20 September - FAA has updated the 14 September clarifying letter to SSA.  Updated version is here.
14 September 2010 - FAA has issued a clarifying letter to SSA regarding FAA AD 2010-18-05.

Current Airworthiness Status of the Blanik L13  05 February 2013
See the "Factual Information" section, below, for details.

The current EASA Airworthiness Directive is  2011-0135, which grounds most Blanik L13s and specifically ungrounds the Blanik L13A.

The AD allows the return to service of L13s
  1. that are in compliance with EASA STC 10035295, or
  2. whose wings have been modified to L13A standards, according to MB L13-112a.

The current FAA Airworthiness Directive is AD 2010-18-05, which grounds the Blanik L13 and L13A in the United States.

Factual information
On 12 June 2010, a Blanik L13 wing separated in flight, resulting in two fatalities.  The accident occurred near Ferlach/Glainach, Austria.

As a result of the accident, the manufacturer, Aircraft Industries a.s. (aka LET) issued a mandatory bulletin L13/109a.  The bulletin prohibited aerobatics, required an inspection, and required a report of the results of the inspection to be sent back to LET.  The mandatory bulletin was published on 18 June 2010, six days after the accident.  See below for information about subsequent bulletins published by LET.

On 30 September 2010 LET published an opinion paper acknowledging the shortcomings of MB L13/109a and stating that a non-destructive eddy-current test was being developed in cooperation with the Prague Aeronautical Research and Test Institute (VZLU).  The paper predicted that the test would become available in 2011.  On 4 October 2010 the official English version of the paper was published.

In a private communication from the product support department on 6 January 2011, Mr. Bruno Kovarik wrote:
"Concerning gliders, our application has been accepted by EASA and project has started already. We are touch with the project manager, we are working on certification programme translation and preparing of conclusive materials. Research institute is processing Eddy current method for crack checking, that will be in next phase tested on samples of critical place with cracks of different sizes with focus on determination of minimal identifiable crack size. We expect to have first results during February 2011."

On 21 March 2011, LET published an update, in which they claim that an inspection is "practically developed," and that they are working on the approval of a modification (probably the LLewellyn modification).

On 16 May 2011, LET published a Mandatory Service Bulletin, MB L13-112a, which authorized the return to service (with lifetime limits) of the L13A model and any L13s that have been modified to L13A standards.  The bulletin describes a procedure for determining the status of each glider, and specifies that the status be reported back to LET, who would then reply with the approved lifetime limit of that particular glider.

On 18 May 2011 LET published another update.  In it, they state that a factory-approved inspections may become available by July 2011, and they refer to the AD&C modification.

The European Aviation Safety Agency (EASA) reacted to the original mandatory bulletin by issuing a series of Emergency Airworthiness Directives.  The first one 2010-0119-E (18 June 2010) simply adopted the LET bulletin, making compliance mandatory within Europe. A few days later (23 June 2010), EASA issued a new AD (2010-0122-E) which superseded the old one, differing only by the inclusion of the L13A model. Upon further reflection, EASA published the third AD, 2010-0160-E on 30 July 2010. The third one superseded the other two. 

The third EASA AD states that, in the opinion of EASA, the inspection described in the original mandatory bulletin
"might not be sufficient for detecting the crack which means that the unsafe condition might still be present even if the sailplane has passed the inspection"

The third EASA AD incorporates all the required actions of the previous two EASA ADs and adds a set of conditions that must be met before continued operation of the glider is allowed. The conditions pertain to the recorded history of aerobatics, winch launching, and 2-pilot operations. If the conditions are not met, or if the records don't exist, then the aircraft is grounded in Europe.

Apparently realizing that the accident glider itself met the criteria for continued flight operations specified by the third AD, on 3 September 2010, EASA issued the fourth AD, 2010-0185-E, which grounded the glider in Europe.

EASA certified the AD&C spar modification as STC 10035295 on 14 June 2011, and approved the STC as an Alternate Means of Compliance with the fourth AD six days later.  Gliders with this modification are now allowed to fly in Europe.

On 20 July 2011, EASA issued its fifth AD, 2011-0135, which supersedes the other four.  This AD adopts the approach of LET MB L13-112a.  This action ungrounds (in Europe) the L13A and any L13s whose wings have been modified to L13 standards.

On 28 February 2012, EASA issued Revision 1 of STC 10035295.  The revision removes all restrictions regarding 2-pilot operations and extends the lifetime of gliders not used for aerobatics to 5000 hours.

In 1971 the FAA issued Type Certificate G24EU to the Blanik L13.

FAA did not issue an AD as a result of the original EASA AD.  However, twenty days after EASA issued the second AD (i.e. 13 July 2010), FAA published AD 2010-14-15.  The FAA AD was essentially identical to the EASA AD, differing only in the magnifier required to perform the inspection.  As a consequence of copying the EASA means of compliance, FAA mandated that the inspection report be sent to LET (and not to FAA).

On 25 August 2010, shortly after publication of the third EASA AD, FAA issued AD 2010-18-05, which superseded AD 2010-14-15.  This, the second FAA AD, refers to the third EASA AD and essentially copies it (including the reference to the "L13A" model, which does not exist in the FAA Registry).

The differences between the third EASA AD and the second FAA AD are important.

The third EASA AD supports a philosophy that airworthiness (in general) can be ascertained by a combination of inspections, modifications, and logbook records.  The third EASA AD constructs such a combination that allows continued flight operations of the Blanik L13 in Europe.

The FAA, on the other hand, relies solely on a program of inspections and modifications, and devalues logbook records.

The second FAA AD makes this point by not mentioning logbook records here:
"The FAA is relying on an inspection and/or modification program approved specifically for this AD to detect and correct cracks before further flight."

The AD further states that the logbook information critical to compliance with EASA 2010-0162-E, is not required to be recorded in the logbooks of US-registered aircraft.  As a result of FAA AD 2010-18-05, the Blanik L13 is grounded in the United States.  The aircraft is grounded even if it can be shown to be in compliance with the third EASA AD.

The discrepancy between the United States and Europe disappeared on 3 September 2010 when EASA published its fourth AD (2010-0185-E), which grounded the glider in Europe.

FAA leaves the door open for future flight operations with this statement:
"To address this problem, before further flight after August 30, 2010 (the effective date of this AD), incorporate an FAA-approved inspection and/or modification program developed specifically for this AD. Corrective action is considered FAA-approved if it is approved by the State of Design Authority (or their delegated agent)."

"Until such a program is approved, owners/operators may apply for an alternative method of compliance (AMOC) following 14 CFR 39.19 described in paragraph (f)(1) of this AD."

This states clearly that, in the USA, the burden of creating a solution that will allow the Blanik L13 to fly again rests solely on the owners/operators of this type of glider.  (There are approximately 193 of them, according to the registry.  The number is approximate because multiple aircraft codes have been used for the L13).

On 14 September 2010, FAA wrote a letter (original version, updated version) to SSA containing factual information about the accident glider, the construction of the wing spar, inspection methods, and the justification for AD 2010-18-05.  The letter is intended to clarify the situation as of 14 September, and it does not contain any advice or proposals for solutions.

The letter confirms that, according to FAA
  • The date of manufacture, total time, and total number of flights of the accident aircraft are uncertain.

  • The problem is in the wing, not the fuselage.

  • Any inspection/modification program must be approved by LET and EASA before FAA will consider approving it.

  • The Blanik L13AC is not affected by AD 2010-18-05.
Both the original version and the updated version are dated 14 September 2010.  The updated version contains minor editorial corrections and more complete references to FAA publications.

At the February 2012 SSA Convention, FAA released a statement regarding the status of their potential approval of the AD&C modification as an Alternate Method of Compliance with AD 2010-18-05.  The statement implies that the AD&C solution (previously approved by EASA) is the only AMOC under consideration and that the FAA Small Airplane Directorate is not developing a solution on its own.

The Government Liaison Committee of the Soaring Society of America has been in communication with FAA on this matter.  SSA members can read the latest reports from the Committee here.  (A login is necessary to see this page).

On 18 September 2010, SSA sent a letter to LET urging them to find a solution as soon as possible.

Transport Canada
The Canadian Authority has adopted, without modification, the first four EASA ADs.  The Blanik L13 is grounded in Canada.

GFA (Australia)
The Gliding Federation of Australia (GFA) is responsible for glider certification in that country (as delegated by CASA). They have developed an extensive maintenance program for the L13. In the 1980s, they established a total hours lifetime limit for the L13, and have subsequently published a pair of ADs describing inspections and/or modifications that allow extension of the limit.  On 27 October 1989, GFA pubished GFA AD-369 which describes three separate programs of inspections and/or modifications to allow service life extensions.  One of them, the "Llewellyn Modification," involves replacing the carry through member and is described in GFA AD-160 (4 May 1990).  Gliders so modified have received Supplemental Type Certificate 96-1 and are re-designated "Blanik L13 A1" in Australia.

On 23 September 2010, Mr. Llewellyn kindly provided this information:
1.    STC 96-1 was issued to Riley Aeronautics in 1979.  Riley aeronautics no longer exists, and the STC holder is now Dafydd Llewellyn.  The drawings and stress analysis for the STC were done by Dafydd Llewellyn.

2.    The original drawings exist, as does the original stress analysis.  Both are held by Dafydd Llewellyn.

3.    Both CASA and the GFA are aware of the above.

4.    The modification involves reinforcement of the lower wing spar cap, replacement of the root ("hinge") fitting, replacement of the lower fuselage carry-through member, replacement of the tailplane spar root fitting with steel ones, reinforcement of the tailplane rear-spar carry-through structure, and reinforcement of the tailplane spar; and the addition of an external steel doubler to the base of the fin.

5.    The modification does require accurate jigging to ensure correct location of the new lower wing root fitting, and of the carry-through member in the fuselage.  As the reinforcement does require that the wing be opened, it is also necessary to support the wing accurately so that no unintended twist is introduced.  This means, the work needs to be done by a suitably-equipped aircraft maintenance shop.  The necessary machined steel parts have to be manufactured under appropriate quality-control.  At present, no appropriately-approved aircraft maintenance shop in Australia or New Zealand has expressed interest in performing the work.

6.    The modification gives a life extension from 3750/4000 hours, as justified by VZLU Report Z31 (1977), to 11,250/12000 hours.  These lives apply only to aircraft whose aerobatic usage does not exceed 2% of TTIS.

7.    The criterion by which wings are accepted for life extension, is by eddy-current inspection of the bores of the critical rivet holes in the spar material, in the wing root area.  A probe capable of detecting cracks less than 0.5 mm is required;  and the holes are later reamed 2mm oversize.  The highest-time aircraft modified so far had 7750 hours TTIS and tested crack-free;  whereas the aircraft in the Austrian crash failed at 2217 hours.  This reflects the great variability caused by aerobatic usage.  The risk of wings being rejected due to cracking obviously increases with the TTIS of the aircraft, but more importantly, with aerobatic usage.

8.    Negotiations are currently under way to have this modification made available in Europe.

The Llewellyn Modificaton is approved only in Australia and New Zealand.  As of February 2011,  there were no maintenance facilities performing the modification (but see below).  There are no reciprocal agreements that would allow the adoption of the Australian STC 96-1 by any other aviation authority.  No modification kits currently exist, and drawings are not available.

On 25 June 2010, GFA issued GFA AD-663 which is based on the second EASA AD (the one that requires only an inspection before further flight), so the L13 could still fly in Australia, as of that date.  Interestingly, GFA AD-663 does not apply to the Blanik L13 A1 glider.

Whether every Blanik L13 was actually grounded in Australia is subject to debate.  On 21 July 2010, GFA published an "update to GFA AD-663," (since removed from the GFA website) which does not appear to be a new AD.  In the update, the GFA Senior Technical Officer for Airworthiness (STO) states:
"To the best of my knowledge there are no Blaniks in Australia which can meet the average operating conditions, so effectively our L-13 fleet is grounded until further notice."

Whether this is an opinion or a directive is not clear.  GFA prohibits the redistribution of an email exchange between the STO and LET, which GFA has published here.

On 14 September 2010, GFA issued an ALERT that states that all L13, L13A, and L13 A1 gliders are indeed grounded in Australia.

On 10 February 2011, GFA published an announcement that certain L13 A1 gliders have been exempted by CASA from EASA 2010-0185-E, and indicated that the Llewellyn modification will again be available (from Southdown Engineering). The announcement was repeated in the GFA President's newsletter in late February.

CAA (New Zealand)
The New Zealand CAA has issued four ADs which follow very closely the first four EASA ADs.  The Blanik L13 is grounded in New Zealand.  CAA publishes all current ADs for each type aircraft in a single document, deleting superseded versions. It is also worth noting that AD DCA/BLAN/5B allows the L13 service life extension by certifying the Australian modifications described above.  New Zealand, however, does not re-designate the aircraft type following the modifications.

On 1 September 2010, the British Gliding Association (BGA) made compliance with the third EASA AD mandatory by publishing this Technical News Sheet.  On 6 September 2010, notice of the grounding of the Blanik L13 was published on the BGA website.

On 4 July 2011,  BGA published a Technical Note stating that the expertise needed to carry out the AD&C modification does not currently exist in UK.

CAA (South Africa)
The South African CAA has adopted all four EASA AD's, without modification.  The Blanik L13 is grounded in South Africa.

CAA (Czech Republic)
As a member state of the European Union, Czech Republic is subject to EASA regulations.  Despite this, the Czech CAA has resisted the grounding of the Blanik L13 by EASA.  CAA published their version of the story in the Czech language (but not in English).  With the cooperation of LET and the Czech Aero Club, the Czech CAA has developed an exemption from EASA AD 2010-0185-E.  Certain Blanik L13s will be allowed to fly in the Czech Republic until the exemption expires in November, 2010 April 2011.

DNA (Argentina)
In Argentina, DNA republishes foreign ADs.  So far they have republished the first three EASA ADs without modification, which implies that the Blanik L13 will soon be grounded in Argentina.

AD&C (Germany)
On 10 March 2011 Aircraft Design and Certification (AD&C) announced a factory approved inspection and modification procedure and has offered a Supplemental Type Certificate (STC ADxC-DC-39-001) for sale.  EASA certified the modification as STC 10035295 on 14 June 2011, and approved the STC as an Alternate Method of Compliance (AMOC) to the EASA AD.  The corresponding FAA approvals should follow.  AD&C has published a FAQ on the STC. They have provided this order form for the STC.

On 2 March 2012 AD&C announced that EASA had published Revision 1 of STC 10035295, which extends the life of gliders that have incorporated the AD&C modification to 3750 hours with up to 2% aerobatics, and 5000 hours without aerobatics.  The announcement also answers questions about the modification and its cost.

At the end of March, 2011, Blanix, the aerobatics team sponsored by Red Bull, began flying again, with the AD&C modification. 

Blanik America
At the beginning of April, 2011 (ten months after the accident), the US agent, Blanik America, began to update their website with news about the progress of the efforts to return the L13 to flying status.

Blanik Aircraft CZ
April, 2015:  Aircraft Industries, a.s. and LET are no longer the type certificate holder for the Blanik L13.

A new company, Blanik Aircraft CZ s.r.o., has been formed to produce a new variant of the L23.  According to its website, the new company "was settled in 2014 as subsidiary of Blanik, Ltd. Company, which is owner of all Blanik type certificates."  Blanik Aircraft CZ is prepared to develop and certify an independent modification to the L13 wing spar and has undertaken a survey of Blanik owners to ascertain the demand for such a modification (update via Michael Derry).

Contact information
The manufacturer, or Type Certificate Holder, is Aircraft Industries, a.s.  Former business names are LET Aeronautical Works and LETECKÉ ZÁVODY a.s. Ask for Customer Support.

Aircraft Industries, a.s.
Na Záhonech 1177
686 04 Kunovice
Czech Republic

Phone: +420-572816002, +420-572816004
Fax: +420-572816006
Email: ots@let.cz

Vitek Siroky
Blanik America, Inc.
P.O. Box 1124
Wenatchie, WA  98807-1124

Phone:  +1 509-884-8305
Fax:  +1 509-884-9198

Airworthiness Directives
Safety Management & Research Section
Certification Directorate
European Aviation Safety Agency
Postfach 10 12 53
D-50452 Koeln, Germany

For further information about AD 2010-18-05, or to submit an Alternate Means of Compliance:
Greg Davison,
Aerospace Engineer
Small Airplane Directorate
901 Locust, Room 301
Kansas City, MO 64106

phone: +1 816-329-4130
fax: +1 816-329-4090

To submit a comment on AD 2010-18-05 (deadline for comments:  12 October 2010)
U.S. Department of Transportation
Docket Operations, M-30
West Building Ground Floor, Room W12-140
1200 New Jersey Avenue, SE.
Washington, DC 20590
Fax: +1 202-493-2251
Go to http://www.regulations.gov and follow the instructions.
Go directly to http://tinyurl.com/3443ugq and enter your comment.

SSA members can look up the Government Liaison Committee on the SSA website and send email to Steve Northcraft and Jim Short.  Non-members should send email to the SSA Office and ask that it be forwarded to the Government Liaison Committee.

Correspondence, Rumors and Speculation
Disclaimer:  the statements made in this section may or may not be true.  If you want to add or remove anything from this section, click here.  Information taken from rec.aviation.soaring will normally not be attributed.

According to a news article, the accident glider was used for aerobatics, and aerobatics were performed during the accident flight.  The glider was in a normal flight attitude, entering the landing pattern, when the spar failed.

While it is fairly common for FAA to ask for engineering feedback from the field, it is fairly unusual (and remarkable) that they did not do so in AD 2010-14-15.  By copying the EASA means of compliance, they mandated that all feedback go directly to LET.  Perhaps they expected LET to issue a follow-up service bulletin.

An L13A is an L13 fuselage with Vivat wings.  The differences are small.

On 17 September 2010 an online petition urging LET to develop a solution was created.

In Australia, EASA AD-0185-E supersedes GFA AD-663 because CASA has made compliance with foreign ADs mandatory since 2009.  Also, apparently, the Australian CASA believes that EASA AD-0185-E applies equally to all Blaniks, regardless of previous modifications.  This was not the original opinion of GFA, but since CASA is the higher authority, GFA has adopted it in principle.  The grounding of the entire fleet of Blaniks in Australia is labeled as an "ALERT" and seems to exist only on that web page.  Update: On 10 February 2011, CASA reversed itself and adopted GFA's original position that the L13 A1 should be allowed to fly.  The L13 A1 was ungrounded.

FAA seems to be focused on the method of attachment of the lower spar cap to the steel "wedge"  (also called "hinge") and the possibility of cracks in the steel wedge.  This suggests that FAA does not believe that there is a problem in the upper spar cap or the fuselage carry through.

Hearsay from FAA (before the 14 September 2010 clarifying letter from FAA to SSA)
An owner/operator of a Blanik L13 (name withheld here) received a return call from Greg Davison (point of contact at FAA for this AD).  This is a summary of the points made during the discussion.  Note: this email summarizes a conversation which took place at the end of August 2010.  Most of points made in this summary were confirmed/clarified by the 14 September 2010 letter from FAA to SSA.

Blanik L-13s are grounded until the factory adequately addresses the wing
spar fatigue crack issues. This could be accomplished by an inspection
and/or modification program. 

During the conversation, Mr. Davison, discussed the issues that concern him
(no significance to the order of listing):

* EASA AD 2010-160-E says "EASA now concludes that the inspection
method (of Mandatory Bulletin No. L13/109a) might not be sufficient for
detecting the crack which means that the unsafe condition might still be
present even if the sailplane has passed the inspection required by EASA AD
2010-0122-E." Apparently cracks were discovered during the subsequent
investigation of the failed spar that cannot be detected by the inpection
detailed by the MB and previous AD.

* The most likely place for cracks to begin, i.e., the outer surface
of the spar cap cannot be seen without removing the outer skin.

* The design of a steel tapered spar cap sandwiched between two
aluminum members and fastened by rivets.

* The skin is fastened to the spar cap by drilling into the rivet
heads holding the spar cap together and then rivets installed to hold the
skin to the spar cap rivet heads which potentially further compromises the
rivets holding the spar cap sandwich together.

* Knowledge, or lack of, the corrosion and fatigue characteristics of
the materials involved.

Mr. Davison said that the reason a US DER may have trouble proposing a
satisfactory solution is that the material details and characteristics are
not known within the US. He also said two other things which will likely

* The FAA will likely issue a document which is intended to clarify
some of the confusion.

* A delegation of folks from the US may go to Europe to discuss these
issues and what to do about them. Participants and date of visit unknown.

I'm willing to help in any way that I can but don't know what would be
helpful at this moment. It does appear that the FAA is waiting for the
factory and EASA to come up with something. Due to the concerns and
unknowns listed above, the FAA will likely be looking to the factory and
EASA to approve any proposals received in the US.

Pass this along to anyone as I am interested if anyone else has received any
information that would shed new light or open up a new avenue allowing us to
resume flying more quickly.

More hearsay
The 1970s vintage Blanik Overhaul and Repair Manuals give all the metal alloys and strength data used in the Blanik L13, as well as a complete spectrum and fatigue analysis.  The manuals specify a service life of 3750 hours, assuming a 5:1 ratio of winch launches to aero tows.

Allegedly factual information from r.a.s.
The accident glider carried registration  OE-0935.

Information about the accident glider, from FAA

 Date of Manufacture 1972 (to be confirmed)
 Serial Number  175117
 Time since new  2318 hours (to be confirmed)
 Cycles since new  5151 (to be confirmed)
 Time since last overhaul  428 hours
 Cycles since last overhaul  853
 Date of last overhaul  February 15, 2000
 Time since last repair/inspection  7 hours
 Cycles since last repair/inspection  17
 Date of last repair/inspection  March 21, 2010   

Informed Opinion
In January 2011, Gerard Robertson, professional engineer and President of the New Zealand Division of the Royal Aeronautical Society, published an opinion paper in the journal, Soaring New Zealand. The paper was subsequently published by SSA.

USA Numbers
The number of gliders affected is difficult to estimate, for two reasons.  The first is that it isn't known how many were airworthy at the time the AD was issued.  The second is that there are five aircraft codes associated with "L13" models.  All five of them refer to the same Type Certificate (G24EU).

The number of aircraft certificated under each aircraft code are as follows (data taken from the FAA Registry on 1 September 2010):

 Code  Manufacturer Name  Model Name  Number of aircraft
 1360306 LET  BLANIK L-13 180
 1360312 LET  L13 AC BLANIK 15
 1360305 LET  L-13 BLANIK  5

The L13AC is the (physically different) variant marketed as a fully aerobatic version of the L13.  The original mandatory bulletin from LET applies to "ALL L13, L13A BLANIK gliders," and not to the L13AC.  The 14 September clarifying letter from FAA confirms that the Blanik L13AC is not affected by AD 2010-18-05.

Just to add to the confusion, there is evidence that at least two L13s are erroneously certificated under the code for the L13AC.

Letter from Pavel Rind
Air-Tech Ltd is an EASA-certified Continuing Airworthiness Management Organization authorized to work on Blaniks.  On 23 February 2011 Pavel Rind of Air-Tech wrote:

Yes, we are in close touch with LET and at this moment the new inspection method is developed and all documents and details about the wing root area inspection were sent to EASA for the final approval. If everything goes smooth we expect that at the beginning of March more information will be released.

The new inspection will be based on eddy current waves and should 
allow the check of wing root area without opening the wing.

When I get more information, I will contact you.