I am asking this because it is something I have always taken for granted, that is, that both pilots would have to wear them, particularly during the critical parts of a flight.
However on the next image the captain does not wear it, albeit they are close to landing.
Photo © Ismael Jorda
What are the rules about this? In case of a medical emergency - meaning, the PIC suffers a stroke - would not be more practical if the PNF was wearing his headset as well? I now that first you aviate, then you navigate, then you communicate but still..... one less thing to do when you have to fiddle around with the airpline on your own...