NH90 qualification according to damage tolerance

Abstract

The NH90 is the first military helicopter in the world to be qualified according to the new Damage Tolerance requirements, FAR 29 amendment 31. For all Principal Structural Elements1, a Retirement Time and repetitive Inspection Intervals, approved by the Authorities, are included in the Airworthiness Limitation Section of the Instruction for Continued Airworthiness. The Retirement Time is based on the conventional "Safe Life" concept. The repetitive Inspection Interval is established by using one of the three offered concepts ("Flaw Tolerance", "Crack Tolerance" and "Multiple Load Path"). The advantage of this pragmatic approach is to improve what exists today, i.e. the substantiation of repetitive Inspection Intervals with full-scale tests and/or analysis, formerly based on in-service experience. This paper presents the necessary research program undertaken by EURO-COPTER to deal with these new concepts and the full qualification process for some dynamic components. It is concluded that the Damage Tolerance philosophy is viable and should contribute to enhance the flight safety of helicopters.