Regarding vehicle accidents, which form primarily documents the operator's account of an incident?

The SF 91, also known as the "Motor Vehicle Accident Report," is specifically designed to document the details surrounding vehicle accidents. This form is utilized to collect factual information, such as the operator’s account of the incident, circumstances of the accident, road conditions, injuries, and damage to property. Its primary purpose is to provide a comprehensive narrative from the operator's perspective, which is essential for investigations, insurance claims, and determining accountability.

In contrast, the other forms mentioned serve different purposes: the DT Form 517 is typically used for reporting a motor vehicle operator's record of duty status, the DD Form 500 is a report of casualty, and the DA Form 2408 records equipment maintenance and inspections. These forms do not specifically document the operator's account of an accident, making the SF 91 the appropriate choice for this scenario.