NTSB reporting requirements are spelled out in Part 830.15, and they’re also pretty simple. The operator shall file a report within 10 days of an accident. An accident is defined as “an occurrence… in which any person suffers death or serious injury, or in which the aircraft receives substantial damage.” Any of the other events listed in 830.5 are reported “only if requested by an NTSB representative”.
shall immediately … notify the NTSB … when (a) An aircraft accident or any of the following incidents occurs: 1) Flight control malfunction, 2) A flight crewmember can’t complete his duties, 3) Failure of certain parts of turbine engines (note: this part says nothing about failure or partial failure of a reciprocating engine), 4) In flight fire, 5) Midair collision, 6) Damage to property over $25,000, and 7) several other events in a large multiengine airplane.