AD&C offers an STC to regain airworthiness of the Blaník L-13 grounded by EASA-AD-2010- 0185-E

Neckargemünd, (PresseBox) - It is the worldwide most produced glider, but not allowed to fly anymore. The European Aviation Safety Agency (EASA) issued Airworthiness Directive (AD) EASA-AD-2010-0185-E as preventive safety measure in the course of investigation of the June 12th, 2010 Blaník L-13 glider accident in Ferlach/Austria. Investigation of this crash has not been officially concluded yet. The AD prohibits any further flight. The US American Federal Aviation Administration (FAA) and many other airworthiness authorities followed EASA and published respective measures.

Aircraft Design and Certification Ltd. (AD&C) is developing a supplemental type certification (STC), including a structural modification as well as an inspection and replacement program, as method of compliance for EASA-AD-2010-0185-E. The approval process utilized a cooperation arrangement with the type certificate holder Aircraft Industries (formerly "LET"). The STC is now available at AD&C.

The STC is based on elaborate 3D geometry and load path analysis (by reverse engineering) and is verified by high quality finite element method (FEM) calculations and structural testing including strain verification. Even individual rivet/bolt load analysis has been performed to identify the root cause of the problem. The well known and approved load spectra KosMos, incorporating a realistic quantity of aerobatic maneuvers, is adapted and applied for the analysis of the Blaník wing and fuselage carry through sections. Further analysis includes the horizontal tail attachment area. Based on the findings of the analyses 3 new parts have been designed and installed to improve the load transfer from wing spar to fuselage. Hi-Lok® bolts, known to have superior fatigue resistance, are used to exchange the critical rivet in rivet spar cap connections and to ease later inspections in the affected areas.

The structure of the Blaník, when healthy, has proven for decades to be safe within the limitations of the airplane. However, after many years of operation, potential occasional abuse, repair, maintenance and overhaul, the determination of whether a given structure is still healthy is a challenging task. Inspection by advanced, affordable as well as proven methods for detection of cracks does not on its own allow declaring critical areas healthy. Crack propagation analysis on the original structure by AFGROW using stress intensity factors of the aforementioned FEM analysis have shown that crack growth in the area of concern, if unchanged, can quickly become uncontrollable.

AD&C expresses their gratitude for the support received in the development of the modification and inspection program to Aircraft Industries (Kunovice, TC-holder), Wolf Hirth GmbH (Kirchheim/Teck, parts production), ATG (Prague, non-destructive testing), Schur NDT (Hamburg, consultancy on NDT/Eddy current testing), MP Magnetische Prüfungen (Reutlingen, production of Eddy current test normal). Special thanks go to AirTech s.p.o.l. (Holešov), a Part-145 approved organisation which undertook the initial installations and is available for your airplane modification. Likewise special thanks go to the Red Bull Blanix- Spiegelflugteam of Austria who made the STC possible by faithfully offering their airplanes to us for the initial modification and structural testing.

Currently the STC is at final approval stage by EASA; approval by FAA has been applied for. Current types of aircraft are the L-13, the L-13A will be included shortly. The permissible operational life of the modified area is prolonged to a total of at least 6000h (irrespective of the accuracy of individual historical records), however the limitations of the rest of the aircraft cannot be changed, without according in depth analysis, from the original 3750h. AD&C is considering a further program for a general life time extension, pending on market response.

The modification can be installed at any Part-145/Part-M or equivalent approved maintenance organisation having the Blaník within their scope of approval. In the course of the modification, personnel approved (EN 4179 or NAS 410) for non-destructive testing utilizing Eddy current, optical (borescope) and dye penetrant inspection techniques is required.

Aircraft Design & Certification ltd

AD&C is a small, but international and efficiently operating engineering service provider with EASA Part 21 Subpart J Design organization approval. AD&C, based in Neckargemünd/Germany, was founded in 2005 by Dipl.-Ing. Marcus Basien and Dipl.-Ing. Boris Kölmel. The aviation experience background covers three decades on four continents and ranks from numerous general aviation type certification projects to specific experimental airplanes like the SolarImpulse, where AD&C staffed design and certification leading functions. Further information can be drawn from the AD&C website

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