FAA, to establish an experimental permit regime for developmental reusable suborbital rockets. Under the CSLAA, FAA can issue experimental permits rather than licenses for the launch of and reentry of reusable suborbital rockets. Previously, FAA could only issue a license for these operations. Congress directed that experimental permits could be issued for: Research and development to test new design concepts, new equipment, or new operating techniques; Showing compliance with requirements as part of the process for obtaining a license; or Crew training prior to obtaining a license for a launch or reentry using the design of the rocket for which the permit would be issued.
https://www.faa.gov/about/office_org/headquarters_offices/ast/licenses_permits/sub_orbital_rockets/
Final Rule - Experimental Permits for Reusable Suborbital Rockets (PDF), April 6, 2007. 14 CFR Chapter III Part 440 (PDF) - Commercial Space Transportation Financial Responsibility Requirements for Licensed Launch Activities