Cockpit Voice Recorders

Missing Evidence About the September 11th Flights

Cockpit voice recorders (CVRs) record all of the conversations between the pilots and air traffic controllers. They are contained in black boxes that are designed to survive the worst fiery crashes and, like the flight data recorders, are recovered after crashes to determine what went wrong.

The only plane whose cockpit voice recorder was supposedly recovered and successfully read was Flight 93. The recorders on the other three jets were deemed unrecovered or too damaged to read. The FBI refused to release an audio record or transcript of Flight 93's voice recorder with the excuse: "we do not believe that the horror captured on the cockpit voice recording will console them in any way." ¹   Then, in April of 2006, a transcript of Flight 93's CVR was published in conjunction with the trial of Zacarias Moussaoui.

After the December 21, 2001 announcement by the FBI that it had deciphered Flight 93's CVR but would not release information about it, Accuracy in Media submitted a Freedom of Information Act requesting to have a transcript released but the FBI refused to comply. ²  

According to the NTSB:

The content and timing of release of the written transcript are strictly regulated: under federal law, transcripts of pertinent portions of cockpit voice recordings are released at a Safety Board public hearing on the accident or, if no hearing is held, when a majority of the factual reports are made public.

Thus federal law apparently would have required the release of the contents of the Flight 93 CVR when the 9/11 Commission closed its doors in late 2004.

Cockpit Voice Recorder Time recorded 30 min continuous, 2 hours for solid state digital units Number of channels 4 Impact tolerance 3400Gs / 6.5 ms Fire resistance 1100 degC / 30 min Water pressure resistance submerged 20,000 ft Underwater locator beacon 37.5 KHz; battery has shelf life of 6 years or more, with 30-day operation capability upon activation 3

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References

1. FBI won't release Flight 93 tape, CNN.com, [cached]
2. What Are They Hiding About Flight 93?, Philadelphia Daily News, 12/28/01 [cached]
3. Cockpit Voice Recorders (CVR) and Flight Data Recorders (FDR), NTSB.gov,