Section 831.50 - Applicability of this subpart(a) The regulations in this subpart apply when the NTSB is leading a marine or major marine casualty investigation.(b) In a marine or major marine casualty investigation led by the United States Coast Guard (USCG), this subpart applies if: (1) Upon USCG's request for assistance, the NTSB is leading an associated investigative activity; or(2) Upon coordination with the USCG, the NTSB elects to collect, test or analyze additional evidence beyond the scope of the USCG's investigation.