46 CFR §4.04-3

The owner, charterer, managing operator or agent of a vessel 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), shall immediately notify the Coast Guard if more than 48 hours have passed since receiving communication from the vessel. This notification shall be given to the Coast Guard district RCC cognizant over the area the vessel was last operating in.