The crew interphone system shall-
(a) provide a means of two-way communication between the flight deck and the other crew members;
(b) be readily accessible for use from each of the required crew stations on the flight deck;
(c) be readily accessible for use at the other crew stations;
(d) have an alerting system incorporating aural or visual signals for use by flight crew members to alert the other crew and for use by the other crew to alert the flight crew;
(e) have a means of the recipient of a call to determine whether it is a normal call or an emergency call; and
(f) provide on the ground a means of two-way communication between ground personnel and at least one flight crew member, if the design of the helicopter requires such interphone system.