Some new speculation has hit the Norwegian press. Some of the information can be relevant if true. What seems to be the original article, by Bergens Tidende, is unavailable to me because it's behind a paywall, but the link is here for those with access:
Warned about loose bolts in 2006.
An open article referencing this has been published by a Norwegian tabloid named Verdens Gang:
Issues with helicopter bolts known for ten years. English Google translate version
here.
I'm not going to translate the whole article, but I'll try to sum it up:
- EASA warned about problems with the attachement bolts back in 2006.
- They reference EASA AD 2006-0163R1 : Fuselage - Main Gearbox (MGB) Suspension Bar Attachment Fittings - Checks which applies to 225 and L2. The AD require regular checks for the suspension bar attaching fitting bolts torque. If over-torque is found, both the bolts and the fitting is also to be inspected for cracks.
- Kåre Halvorsen from AIBN are said to have confirmed to Bergens Tidene that parts of some of the bolts were found in the airframe while others were absent (although no description of the state of the threads in the airframe is given).
- CHC claim to have performed the required regular checks.
If I interpret this correctly and the threads in the airframe are intact it's hard to se how these can have unscrewed during the accident. I would think that the bolts would either snap leaving the threaded part behind or rip the threads out of the airframe. In the case of snapping I would think that enough damage would be done to the threads that they would be stuck there on the way down instead of being able to be unscrewed by vibrations.
If this is correct and has been known this whole time I can certainly see how AH can be this convinced of what the cause is. What I have trouble understanding is how such an apparant design flaw can be left there for 10 years without any changes to the fittings or the bolts being designed, and simply relying on that the AD with the extra checks will make up for the design flaw.