The Cockpit Voice Recorder
The CVR would be better named the cockpit audio recorder as it provides a record of the total audio environment in the cockpit area. This includes crew conversation, radio transmissions, aural alarms, control movements, switch activations, engine noise and airflow noise.
The CVR retains the last 30 minutes of information on tape operating on the endless-loop principle.
Approximately 80% of aircraft accidents involve human factors which, in most cases, means crew performance was a factor. Consequently, the CVR often assists accident investigators to determine why an accident occurred.
The Flight Data Recorder
The FDR records flight parameters. The range and quantity of data recorded varies widely, depending upon the age and size of the aircraft.
The minimum requirement is to record a basic group of five parameters:
- Pressure altitude
- Indicated airspeed
- Magnetic heading
- Normal acceleration
- Microphone keying.
Microphone keying (i.e. the time radio transmissions were made by the crew) is recorded to correlate FDR data with CVR information.
This basic requirement has existed since the 1960s, and today, modern jet aircraft far exceed this basic requirement, being fitted with FDRs that can record up to 400 parameters covering all aspects of the aircraft operation.
The FDR retains the last 25 hours of aircraft operation on tape and, like the CVR, operates on the endless-loop principle. As FDRs have a longer recording duration than CVRs, they are very useful for investigating both incidents and accidents.
The FDR often tells accident investigators what happened during an accident sequence.
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