"North Sea lelicopter crash causes revealed"
- is the title of a short article in the 14 August issue of Professional Engineering magazine. I've extracted a few bits, which may interest people here...
On 16 July, a Sikorsky S-76, owned by Bristow was ferrying oil workers between installations in the Shell field when it crashed 28 miles NE of Cromer. The wreckage was recovered and has been under investigation.
Upon inspection, it was noticed that one of the four rotor blades had a fracture, not consistent with the crash. Additionally, the casing of the main rotor gearbox had fractured and the gearbox and rotor head had broken away from the fuselage mountings in flight.
Analysis by research company Qinetiq on the blade indicated that it fractured due to fatigue before the outer portion separated. From this, it was clear that the blade fracture had initiated the event; the gearbox had separated from the fuselage mountings due to the severe imbalance created by the loss of the separated blade section.
Microscopic investigation of the fatigue point hinted that it had suffered intense thermal damage in the past..... It was ascertained that the rotor blade was struck by lightning in 1999 while fitted to another helicopter, thereby causing the damage.
Sikorsky has agreed with the AAIB findings and has removed from service any main rotor blade identified as having been damaged by lightning. Appropriate action has been taken by both the FAA and CAA.
G