What agency investigates aircraft accidents and determines their probable causes?

The National Transportation Safety Board (NTSB) is responsible for investigating aircraft accidents and determining their probable causes. This agency plays a critical role in enhancing aviation safety by examining the circumstances surrounding an accident, including the actions of the flight crew, maintenance history, and environmental factors. The findings from NTSB investigations often lead to recommendations for improved safety protocols and regulations, which can significantly influence aviation policy and operations.

In contrast, the Federal Aviation Administration (FAA) primarily focuses on regulating and overseeing civil aviation to ensure safety and compliance with federal aviation laws but does not conduct accident investigations. The Department of Transportation (DOT) oversees various transportation modes but does not specifically investigate aviation accidents, and the National Aeronautics and Space Administration (NASA) is primarily involved in space exploration and aeronautics research rather than accident investigations. Thus, the NTSB's specialized role in accident investigation underscores its importance in the aviation safety framework.