25 C.F.R. § 1000.90
If the effective date of the successor AFA is not on or before the expiration of the current AFA, subject to terms mutually agreed upon by the Tribe/Consortium and the Department at the time the current AFA was negotiated or in a subsequent amendment, the Tribe/Consortium may continue to carry out the program authorized under the AFA to the extent adequate resources are available. During this extension period, the current AFA shall remain in effect, including coverage of the Tribe/Consortium under the Federal Tort Claims Act (FTCA) 28 U.S.C. 2671 - 2680 (1994), and the Tribe/Consortium may use any funds remaining under the AFA, savings from other programs or Tribal funds to carry out the program. Nothing in this section authorizes an AFA to be continued beyond the completion of the program authorized under the AFA or the amended AFA. This section also does not entitle a Tribe/Consortium to receive, nor does it prevent a Tribe from receiving, additional funding under any successor AFA. The successor AFA must provide funding to the Tribe/Consortium at a level necessary for the Tribe/Consortium to perform the programs, functions, services, and activities or portions thereof (PFSAs) for the full period it was or will be performed.
25 C.F.R. §1000.90