Which Records Can Help Show What Happened
If you are wondering what proof exists, it usually falls into a few groups. Flight data recorder (FDR) and cockpit voice recorder (CVR) data can matter, but only where the aircraft carried them; not every business aircraft does. Other evidence includes air traffic control radar and voice recordings, aircraft maintenance logs, records of compliance with airworthiness directives, crew training and qualification records, weather data, and the physical wreckage.
Airworthiness directives (ADs) are mandatory safety instructions the FAA issues for aircraft, engines or components. Whether required directives were complied with can be relevant where maintenance is in question.
During an active investigation, the NTSB controls the wreckage and primary evidence. Cockpit recordings carry their own federal limits: under 49 U.S.C. § 1154(a), a party in a judicial proceeding generally may not use discovery to obtain a cockpit recorder recording, or transcript portions and still images the NTSB has not made public, unless a court allows it after a private (in camera) review finds the public material insufficient for a fair trial; where a court allows it, the court issues a protective order limiting its use to that proceeding, and the material may be admitted only under seal.
Because so much of the primary evidence sits with others, the records on a family's own side can carry real weight. If you were hurt, or lost someone, those usually include medical records, photographs and video from the scene or the aftermath, the aircraft's public FAA registration and ownership records, incident and first-responder reports, and the names and contact details of witnesses. Families often gather these slowly, sometimes long after the first shock, and that is normal.
What is available, from whom, and when it can be obtained differs from case to case. If you would like to talk through what records exist in your situation, you can request a case evaluation.