CAT.IDE.H.180 Public address system
(a) Helicopters with an MOPSC of more than nine shall be equipped with a public address system, with the exception of (b).
(b) Notwithstanding (a) helicopters with an MOPSC of more than nine and less than 20 are exempted from having a public address system, if:
(1) the helicopter is designed without a bulkhead between pilot and passengers; and
(2) the operator is able to demonstrate that when in flight, the pilot’s voice is audible and intelligible at all passengers’ seats.