100 years ago today, the first fatal accident involving a powered, heavier than air aircraft occurred at Ft. Myer, Virginia. The pilot, Mr. Orville Wright, was seriously injured and the passenger, US Army Lt. Thomas Selfridge, was killed.
Thomas Etholen Selfridge, First Lieutenant, United States Army
Accident Report
The Aeronautical Board of the US Army Signal Corps conducted a formal investigation into the accident and published a comprehensive report. Many of the issues discussed in the report (analysis of the wreckage, survival factors, witness interviewing) are still essential elements of modern aircraft accident investigation.
http://www.flightsafety.org/ap/ap_dec03.pdf
Since then, dedicated professionals all over the world have investigated thousands of accidents and serious incidents so that "from tragedy we draw knowledge to improve the safety of us all".