25 U.S.C. § 1621l: Patient travel costs

an adult escort (including a parent, guardian, or other family member) who is required because of the physical or mental condition, or age, of the applicable patient; a health professional for the purpose of providing necessary medical care during travel by the applicable patient; or other escorts, as the Secretary or applicable Indian Health Program determines to be appropriate. emergency air transportation and non-emergency air transportation where ground transportation is infeasible; transportation by private vehicle (where no other means of transportation is available), specially equipped vehicle, and ambulance; and transportation by such other means as may be available and required when air or motor vehicle transportation is not available.