[jcrawfordor]

The details are nuanced by the definitions in the CFR, the details of the reporting requirements (NTSB must do something with everything reported to it but that may be minimal), and the NTSB's authority to delegate more minor investigations to FAA flight standards. Lots of people in the thread are hashing these out. But it suffices to say that when an airplane is seriously damaged or people are seriously injured, the NTSB is obligated to investigate. This dates way back to before the NTSB existed. In straightforward situations that sometimes consists only of the regional office making some phone calls and then preparing a two-page summary (you see a LOT of these two-page summaries for GA incidents, it's basically a form letter), but that's under the assumption that their cursory review doesn't turn up anything interesting. You can already find this incident in the NTSB's investigation database, WPR22LA049.