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GFA AD 678 Issue 1

INCREASED RISK OF FLUTTER OF THE TAILPLANE AND DEGRADED SECURITY OF THE TAILPLANE ATTACHMENT CAUSED BY LOOSE BOLTS IN THE TAILPLANE ATTACHMENT BRACKET ASSEMBLY AND THE TAILPLANE CONTROL HORN

Applicable to all Schempp-Hirth types/models with all-flying tailplanes. Investigations into loose tailplane attaching bolts have discovered that due to very dry conditions recently experienced in Australia, the plywood tailplane spars have shrunk, allowing the attaching bolts that mount the tailplane to the fuselage to become slightly loose. Such looseness is transferred to the tailplane attachment and may lead to excessive free-play in the control circuit which increases the possibility of flutter occurring during normal operation. Left unchecked, looseness of the bolts may ultimately lead to excessive wear and damage to the tailplane structure. The bolts are retained by nuts at the rear of the spar however these are not captivated and freely rotate with the bolt when shrinkage of the ply has taken place. Access to these nuts is not possible without cutting holes in the fibreglass. This prevents the bolts from being torqued to the correct specifications. Schempp–Hirth have two different methods of attaching tailplanes in this generation of sailplane, and both methods have been found to exhibit the same problem. Of 6 aircraft inspected (both Cirrus and Nimbus 2) 5 were found to have this issue, with varying numbers of loose bolts. One aircraft was found to have all 8 bolts loose. There are 8 x bolt/nut combinations that affix the tailplane to the fuselage. Both methods are shown in the Appendix with information supplied from GFA members. Embodied reference documentation is GFA Safety Alert ASA No. 01/13 (8 October 2013), SCHEMPP-HIRTH Flugzeugbau GmbH Kirchheim/Tech TN No. Gen 4 (New epoxy resin-system for glass, carbon and aramid fibres)Schempp-Hirth Flugzeugbau GmbH Technical Note Gen-5, 15 Mar 2013 Approved Repair Design under (EU) No: 748/2012 and Schempp-Hirth Flugzeugbau GmbH Repair Instruction for loose bolts in elevator attachments - Valid for all-flying tails of Schempp-Hirth gliders.