Final answer:
The aircraft operator or the local authorities are responsible for preserving the wreckage, mail, or cargo until the NTSB takes custody to maintain evidence integrity for the investigation.
Step-by-step explanation:
The entity responsible for preserving the wreckage, mail, or cargo until the National Transportation Safety Board (NTSB) takes custody is the aircraft operator or the authority in charge of the crash site.
This could be local law enforcement or a federal agency, depending on the location and nature of the incident. Once the NTSB is notified of an aviation accident, investigators typically take charge of the scene to ensure that evidence is protected and to begin their analysis.
However, before their arrival, it's crucial to maintain the integrity of the site and any associated materials to aid in the investigative process.