http://www.aaib.dft.gov.uk/bulletin/mar01/gbhbf.htm
Sikorsky S76A (Modified), G-BHBF
The aircraft was in the cruise, en-route from Norwich to the offshore Clipper gas field. Whilst cruising at 2,000 feet in IMC (just above the cloud base) the aircraft was struck by lightning. Approximately 30 seconds later, the crew became aware of a smell of burning. They rapidly descended below cloud and returned visually to Norwich. The landing was uneventful.
http://www.aaib.dft.gov.uk/special/gbjvx/gbjvx.htm 11 souls lost.
This rotor blade was manufactured in March 1981. In 1999 when fitted to Sikorsky S76A G-BHBF it was damaged by a lightning strike (see AAIB Bulletin 3/2001). At that time the blade had accumulated 8,261 hours usage. The blade was returned to the manufacturer for assessment where, following inspection, it was repaired and returned to service. Neither the thermal damage to the spar nor the manufacturing anomaly were detected during this inspection. At the time of the accident, the blade had accumulated 9,661 hours usage. The airworthiness limitation life of the blade is 28,000 hours.
The AAIB and the helicopter's manufacturer are of the opinion that the electrical energy imparted by the lightning strike in 1999 exploited the anomaly that was built into the blade at manufacture and damaged the spar.
There are also some interesting threads on strikes, found via the search function.