This is one of the few places I feel the simple "shouting fire in a crowded theatre" analogy holds true. It's in the greater interest of the overall public good that the parties involved in an NTSB investigation are not given the opportunity to interfere with the process of the investigation.
Also it's not actually a gag order. I can't find any actual legal regulations which leads me to the assumption that this is less an NSL style "comply or you will be silenced" sort of situation. All the evidence I could find makes it seem like more of a "gentleman's agreement" developed over the decades of interacting with an extremely small pool of actors. ( American Railroads + American Truck Makers, and Airlines operating in US airspace ) Infact I grabbed this exemplary ( if a little long ) quote off the NTSB website from a press release regarding the FAA accidentally releasing investigation information when complying with a FOIA request before the investigation was complete. ( The NTSB don't care about the FOIA request, just that you wait until their job is done before answering it.)
>> The NTSB depends upon full participation and technical assistance by the parties in our accident investigations in order to ensure that our investigations are objective, rigorous, and complete. Allowing any party to release investigative information without approval may enable that party to influence the public perception of the investigation and undercut the fairness of the process.
>> Accordingly, we require that any release of information related to an ongoing accident investigation be coordinated and approved by the NTSB prior to its release. When the investigation is complete, these restrictions no longer apply.
Also it's not actually a gag order. I can't find any actual legal regulations which leads me to the assumption that this is less an NSL style "comply or you will be silenced" sort of situation. All the evidence I could find makes it seem like more of a "gentleman's agreement" developed over the decades of interacting with an extremely small pool of actors. ( American Railroads + American Truck Makers, and Airlines operating in US airspace ) Infact I grabbed this exemplary ( if a little long ) quote off the NTSB website from a press release regarding the FAA accidentally releasing investigation information when complying with a FOIA request before the investigation was complete. ( The NTSB don't care about the FOIA request, just that you wait until their job is done before answering it.)
>> The NTSB depends upon full participation and technical assistance by the parties in our accident investigations in order to ensure that our investigations are objective, rigorous, and complete. Allowing any party to release investigative information without approval may enable that party to influence the public perception of the investigation and undercut the fairness of the process.
>> Accordingly, we require that any release of information related to an ongoing accident investigation be coordinated and approved by the NTSB prior to its release. When the investigation is complete, these restrictions no longer apply.