46 C.F.R. § 4.04-3
Reports of lack of communication
The owner, charterer, managing operator, or agent that is required to report to the United States Flag Merchant Vessel Location Filing System under the authority of section 212(A) of the Merchant Marine Act, 1936 (46 App. U.S.C. 1122a), must immediately notify the Coast Guard if more than 48 hours have passed since receiving communication. This notification must be given to the Coast Guard district RCC cognizant over the last known operating area.