the aircraft was equipped with a fairchild industries model a-100 cockpit voice recorder (cvr). however, 21 minutes of the 30-minute tape were blank. tests of the cvr in the aircraft revealed no discrepancies in the cvr's electrical and recording systems.the cvr tape can be erased by means of the bulk-erase feature on the cvr control panel located in the cockpit. this feature can be activated only after the aircraft is on the ground with its parking brake engaged. in a deposition taken by the safety board, the captain stated that he usually activates the bulk-erase feature on the cvr at the conclusion of each flight to preclude inappropriate use of recorded conversations. however, in this instance, he could not recall having done so. the ntsb made the following statement in the accident report: