CAT.IDE.H.145 Radio altimeters
(a) Helicopters on flights over water shall be equipped with a radio altimeter capable of emitting an audio warning below a pre-set height and a visual warning at a height selectable by the pilot, when operating:
(1) out of sight of the land;
(2) in a visibility of less than 1500 m;
(3) at night; or
(4) at a distance from land corresponding to more than three minutes at normal cruising speed.