That's a new one on me. The Board is not inclined to analyze work by FAA investigators unless they were assisting the NTSB investigators in the field. Further, the FAA has neither the facilities nor expertise to assess CVRs and FDR data. Finally, the Board does not issue probable causes when the FAA does an accident investigation.
Nope. On delegated investigations, the FAA will conduct all fieldwork up to and including the preparation of the "Factual Report". This report is then passed on to the NTSB Investigator-in-Charge. The NTSB may then conduct analysis and determine the "Probable Cause."
49 CFR § 831.2 Responsibility of Board.
"(a) Aviation.
(2) Certain aviation investigations may be conducted by the Federal Aviation Administration (FAA), pursuant to a “Request to the Secretary of the Department of Transportation to Investigate Certain Aircraft Accidents,” effective February 10, 1977 ... but the Board determines the probable cause of such accidents or incidents.
Under no circumstances are aviation investigations where the portion of the investigation is so delegated to the FAA by the Board considered to be joint investigations in the sense of sharing responsibility. These investigations remain NTSB investigations."