What needs to happen is for the current Chairwoman to authoriize funds for additonal investigators, and that isn't likely to happen until a new Chair is in place. There have been no external openings for Air Safety Investigators (other than interns) for quite some time.
I wouldn't get my hopes up for getting on with the NTSB any time soon. I know of several experienced investigators waiting for positions, but they just won't approve any money to hire.
However, if you are a student, you can petition your college or university for an internship. If you are exceptional in that position, then they might put you in line for an opening at one of the field offices, should one arise. From there, you can work your way into one of the specialties in DC if you are so inclined.