Temporary restriction on public access followed concern that spectrum analysis could reconstruct UPS crash crew’s voices.
US investigators have largely restored access to a docket system which had been suspended over concerns that sound spectrum images could be used to recreate cockpit audio.
Forty-one dockets remain under review.
The docket for the UPS Boeing MD-11F accident at Louisville last November is among those re-opened — although certain data has been redacted, and some files remain offline.
Reconstructed spectrum data from the MD-11F crash, enabling simulation of cockpit audio that was circulated on social media, had alarmed the National Transportation Safety Board.
Cockpit-voice recorder audio is protected by US federal law and the safety board does not release recordings, only a transcript or a description of relevant information obtained.
In response to the audio reconstructions it restricted access to accident dockets and initiated a review to determine the extent of the issue.
While the safety board has yet to detail the results of its review, and any changes to its procedures, it stresses that its long-standing processes have served to protect sensitive audio and video material.
“All on-board recordings are protected materials, and access to them is tightly controlled,” it says.
“Recordings are secured by investigators, processed and reviewed by specialised recorder experts in the NTSB Recorder Laboratory, and only made available internally to authorised personnel who have a need to access them for investigative purposes.”
It adds that any limited release of recorder-related information to the public is only undertaken after “multiple levels of review and approval”.
The safety board says detailed procedures also govern the handling and sharing of recordings — as well as transcripts, screenshots and other recorder-derived information.
“Any imagery approved for public release is carefully reviewed and, when necessary, redacted to remove identifying or sensitive information,” it adds.
After evaluating “additional safeguards” for investigative material, the safety board has reinstated public access to the docket system and most of the docket information. It has not elaborated on the evaluation or its risk assessment.
“[We continue] to examine the issue to ensure sensitive information is protected while maintaining transparency in [our] investigations,” it says.
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