So whose fault is it? Sikorsky or FAA?
I'm not sure I would use the word
fault, but it is the regulator's
responsibility to write the regulations and then ensure compliance with them.
As such the FAA/EASA know what they wanted (they wrote the regulation) and fully certified the S92 against those regulations.
The reality is that there is not (yet) a heavy helicopter that can loose all of it's MGB lubrication and run for 30 minutes at a cruise power setting without the help of additional backup systems. The only two heavy helicopters certified against the latest FAR29 requirements, the S92 and the EC225, both failed there "run dry" tests. Each manufacturer then took a different route to then obtain compliance and certification. The EC225 MGB was modified with a glycol injection system, giving it 30 minutes until a "Land Immediately". The S92 introduced an oil cooler bypass valve that Sikorsky and the regulators anticipated would stop the only likely cause of oil loss. This scenario does not come with a 30 minutes "Land Immediately" requirement. However we now know that another failure mode is possible with the S92.
So back to the manufacturer and the regulator! Time will tell if any of the parties (FAA/EASA/TC/Sikorsky) are looking to change their position with regard to the S92.
Bottom line is that the buck starts and stops with the regulator IMHO. But Sikorsky does have product image and duty of care/liability to worry about.