The Safety Investigation Board is separate, and privileged.
FNAEB investigates the crew, and usually follows a Class A mishap ($2m damage or hull loss, or death/permanent disabling injury) but can be triggered by near-miss or pilot flathatting etc.
A friend is a retired Naval aviator, said the #1 reason aviators get permanently grounded from the fleet, is refusal to accept responsibility for mistakes that they were clearly responsible for. Things like forgetting to set the altimeter correctly before takeoff, causing a serious near-miss or pilot deviation. Honestly and fully admitting their mistakes, is more likely to result in a FNAEB returning them to the fleet. Asoh Defense comes to mind.[0]
[0] https://en.wikipedia.org/wiki/Japan_Airlines_Flight_2#The_%2...