The aircraft had a cockpit voice recorder (CVR) and it was undamaged. 21 minutes of the 30 minute tape were blank. The remaining 9 minutes of the tape had good fidelity but pertained only to the flightcrew conversations after the aircraft was on the ground at Detroit. Tests showed no discrepancies in the CVR’s electrical and recording systems. The CVR can be bulk erased from the flightdeck after the aircraft was on the ground with its parking brake engaged, but the Captain stated that he usually activates the Bulk Erase feature at the conclusion of each flight but he could not recall having done so this time. The rest of the flight crew stated that they did not erase the tape nor did they see the captain activate the erase button on the CVR control panel.
