Which of the following must a Cockpit Voice Recorder record?

 1. Audio or voice signals identifying navigation or approach aids introduced into a headset or speaker.

 2. The aural environment of the flight deck.

 3. Flight-crew members on the flight deck using the aeroplane's interphone system.

 4. Flight-crew members using the aeroplane's interphone system between cabin crew stations (if installed).

 5. Voice communications transmitted from or received in the aeroplane by radio.

 6. Flight-crew members on the flight deck using the public address system (if installed).