The apparatus comprises one or more acoustical transducers associated with a particular interchangeable rotor blade for monitoring acoustic emissions emitted by the rotor blade under operating stress. The output of the transducers is connected to a computer associated with the particular aircraft. The transducer output signals are processed by the computer and filtered to allow real time stress return level readings so as to accumulate a count of critical acoustic emissions which are indicative of progressive irreversible structural fatigue or damage to the interchangeable rotor blade.
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