49 CFR §831.20

1. (a)Scope. The NTSB is authorized to investigate—
   1. (1)Each accident involving a civil aircraft in the United States, and any civil aircraft registered in the United States when an accident occurs in international waters;
   2. (2)Each accident involving a public aircraft as defined in 49 U.S.C. 40102(a)(41), except for aircraft operated by the U.S. Armed Forces or by an intelligence agency of the United States;
   3. (3)With the participation of appropriate military authorities, each accident involving a military aircraft and—
      1. (i)a civil aircraft; or
      2. (ii)certain public aircraft as described in paragraph (a)(2) of this section.
2. (b)Authority to examine or test. Pursuant to § 831.9 of this part, a credentialed employee of the NTSB is authorized to examine or test any civil or certain public aircraft, aircraft engine, propeller, appliance, or property aboard such aircraft involved in an accident or incident subject to the NTSB's authority.