10 U.S.C. § 2635

(a) The Secretary of Defense is authorized to assist the Department of Health and Human Services and the Department of Homeland Security in providing medical emergency helicopter transportation services to civilians. Any resources provided under this section shall be under such terms and conditions, including reimbursement, as the Secretary of Defense deems appropriate and shall be subject to the following specific limitations: (1) Assistance may be provided only in areas where military units able to provide such assistance are regularly assigned, and military units shall not be transferred from one area to another for the purpose of providing such assistance. (2) Assistance may be provided only to the extent that it does not interfere with the performance of the military mission. (3) The provision of assistance shall not cause any increase in funds required for the operation of the Department of Defense. (b) No individual (or his estate) who is authorized by the Department of Defense to perform services under a program established pursuant to subsection (a), and who is acting within the scope of his duties, shall be liable for injury to, or loss of property or personal injury or death which may be caused incident to providing such services.