Thomas were the failures attributable to FOD and if not was the cause known after tear down? And are you sure it was the power turbine and not the compressor turbine? The only failure I have had in managing over 25,000 hours on 90 series King Airs has been the compressor turbine disk, and both times technically due to FOD. Not saying we have not worked on power sections, but we caught those due to strange noises in the reduction gear box or power section prior to catastrophic failure.