Division (a) Each flight crew member required to be on duty in the flight crew compartment shall wear a headset with boom microphone or equivalent. The headset shall be used as the primary device for voice communications with ATS:F1

when on the ground:

1. (i)

   when receiving the ATC departure clearance via voice communication; and

2. (ii)

   when engines are running;

when in flight:

1. (i)

   below transition altitude; or

2. (ii)

   10 000 ft, whichever is higher;

and

whenever deemed necessary by the pilot in command.