31 July 2011 C1 CIVIL AVIATION DEPARTMENT HONG KONG ...

CIVIL AVIATION DEPARTMENTHONG KONG, CHINAAirworthiness NoticeDETERIORATION OF WOODEN AIRCRAFT STRUCTURESNo. 50Issue 530 September 20051 Concern over the susceptibility of wooden aircraft structures to deterioration, andrecognition that extensive dismantling and inspection may be required to ensure theircontinued integrity was first expressed in earlier Airworthiness Notices in the UnitedKingdom. The Director-General has published this Notice to alert possible ownersof such aircraft to the problems they may face, especially in a tropical environment.2 Examination of older type wooden aircraft has highlighted several serious structuralfailures, and continued vigilance is therefore essential if the integrity of woodenaircraft structures is to be maintained. Deterioration has occurred in thoseassemblies where normal inspection is impossible and has not come to light until theadjacent structure has been disturbed to embody repairs or modifications, or duringextensive overhaul. These closer examinations have revealed failure of glued jointsin the primary structure and patches of timber in a state of decay as a result ofexposure to extremes of atmospheric conditions.3 General conclusions which have been drawn from the results of the examinationsare:-(a)(b)(c)(d)(e)The external appearance of wooden aircraft may give little or no indication ofthe condition of the timber and glued joints beneath the surface.Aircraft built with glued ply and timber torsion box construction are the mostvulnerable.Under extreme conditions, deterioration can be very rapid indeed.Lack of proper drainage can be a significant contributory factor, particularlywhen associated with (c) above.Many glues, especially those in use before 1950, lose strength with age and/orcycles of humidity and temperature.AN-50 P.130 September 2005