According to the Commission Regulation (EU) No 965/2012 of October 2012, Annex IV related to Commercial Air Transport Operations [PART-CAT] Subpart D – Instruments, Data, Equipment (IDE), Section 2 for Helicopters (H), “CAT.IDE.H.345 - Communication and navigation equipment for operations under IFR or under VFR over routes not navigated by reference to visual landmarks”, is prescribed that:

(a) Helicopters operated under IFR or under VFR over routes that cannot be navigated by reference to visual landmarks shall be equipped with radio communication and navigation equipment in accordance with the applicable airspace requirements.

(b) Radio communication equipment shall include at least two independent radio communication systems necessary under normal operating conditions to communicate with an appropriate ground station from any point on the route, including diversions.

(c) Helicopters shall have sufficient navigation equipment to ensure that, in the event of the failure of one item of equipment at any stage of the flight, the remaining equipment shall allow safe navigation in accordance with the flight plan.

(d) Helicopters operated on flights in which it is intended to land in IMC shall be equipped with suitable equipment capable of providing guidance to a point from which a visual landing can be performed for each aerodrome at which it is intended to land in IMC and for any designated alternate aerodromes.

Therefore, at least 2 radios are necessary for conducting instrument flight rules (IFR) or visual flight rules (VFR) navigation without relying on visual landmarks.