Flight Recorders - Cockpit Voice Recorders (CVRs)
Cockpit voice recorders record either the last 30 minutes of audio, or the last
120 minutes of audio depending on the part number of the unit. Only solid state
CVR's will record 120 minutes, but there are both tape based and solid state 30
minute recorders.
Tape Units
Tape units use either an endless loop tape, or a stacked reel to reel with reversing
motors. The recorders record continually writing over the oldest information.
Tape is becoming obsolete; most CVR manufacturers have only a limited amount of
tape left in their inventories.
Only the tape mechanism is protected in the crash and fire protected module.
Tape based recorders require annual maintenance to ensure normal TBO times are met,
and typically 4000 to 6000 hour overhauls
Solid State
Solid state recorders employ non-volatile memory to store digitally recorded audio.
Only the memory is protected in the crash and fire protected module.
Solid state recorders are highly integrated and employ multiple microprocessors
and programmable digital array chips.
Intelligibility Evaluation
The CAR's require that an intelligibility evaluation be performed every 3000 hours
or 12 months which ever occurs first.
The Intelligibility Evaluation confirms that the aircraft CVR system meets the minimum
requirements.
First time installation of CVR's must have the intelligibility evaluation performed
by an TCCA approved Initial Intelligibility Evaluation Center. Pacific Avionics
& Instruments is one of 3 approved facilities in Canada.