BIMs
In my old and bold days I flew Sikorsky designed Wessex and Seakings with similar blade designs to the S76. These blades had hollow spars pressurised with nitrogen and a BIM indicator at the root which was white if the spar was pressurised but turned to white with black stripes if the spar lost pressure due to a crack etc. A BIM may have given warning of the crack before the catastrophic failure occurred.
I believe that the S76 blade spar is a cold formed welded titanium tube which is then hot formed into the required aerofoil shape.
HM