As previously discussed, it is possible that the cracks in each of the three HPT stage 1 disks discussed in this letter were the result of surface damage. However, the Safety Board recognizes that there is no clear evidence of surface damage on the area of the US Airways disk from which the crack originated and, therefore, it is also possible that the crack in that disk initiated from an undamaged blade slot bottom. Further, metallurgical examination revealed that in the area immediately adjacent to the fracture origination point, the radius between the slot bottom and the forward and aft faces of the disk conformed to the engineering drawing requirements for that radius, suggesting that the area from which the crack initiated also conformed. This possibility raises concerns that the design of the slot bottom of the GE CF6- 80C2 HPT stage 1 disk may not provide an adequate margin of safety even when the disk is manufactured to specifications. Further, during the Safety Board’s examination of the separated disk from the US Airways airplane, it was found that many of the radii between the slot bottoms and the forward and aft faces of the disk either exceeded or were less than the engineering drawing requirements for this radius.
Appearently, the problem is still under investigation!
This is the NTSB recommendation. I haven't found anything definitive regarding what the FAA did in response.