49 CFR §171.21

1. (a)A shipper, carrier, package owner, package manufacturer or certifier, repair facility, or person reporting an incident under the provisions of § 171.16 must:
   1. (1)Make all records and information pertaining to the incident available to an authorized representative or special agent of the Department of Transportation upon request; and
   2. (2)Give an authorized representative or special agent of the Department of Transportation reasonable assistance in the investigation of the incident.
2. (b)If an authorized representative or special agent of the Department of Transportation makes an inquiry of a person required to complete an incident report in connection with a study of incidents, the person shall:
   1. (1)Respond to the inquiry within 30 days after its receipt or within such other time as the inquiry may specify; and
   2. (2)Provide true and complete answers to any questions included in the inquiry.