DAMAGE ASSESSMENT METHODOLOGY OF UK APACHE LONGBOW

A battlefield damage assessment and repair technical manual for the AH-64A Apache helicopter was published in 1996. The document provides information and instruction for damage evaluation procedures and expedient repair methods and contains the damage limit criteria under the premise that the maximum utilization of resources can be achieved in a short-time duration, high intensity activities in combat operations through the deferment of damage repair. With the advent of an extensive flight load survey conducted on the AH-64D Apache Longbow helicopter, the opportunity to expand the damage limit criteria has arrived. Structural critical parts are evaluated for the expansion of deferrable damage limits. Major subsystems considered are airframe, flight controls, rotors and drive train. Selection of the components is predicated on factors such as structural integrity, functional performance, hit/kill ratio, cannibalization rating and deferability. The parts subject to analysis have both cycle count data during the flight load survey and failure history during the qualification test. A detailed methodology based on damage tolerance principles is presented. The analysis entails finite element modeling and iterative crack growth analysis under the spectrum loads. The serviceability criteria are determined on the basis of the expanded damage limits as a function of the calculated fatigue life. The results of this investigation are used to assist an assessor in the process of battle damage inspection, evaluation and decision making for deferment or repair with the aid of a triage assessment. The assessor will then determine the criticality of the situation in regard to the airworthiness and mission capability of the wounded rotorcraft.