Singapore legislation
Regulation 55
of Air Navigation (135 — Commercial Air Transport by Helicopters and Small Aeroplanes) Regulations 2018
Regulation 55
Flight crew communication
An AOC holder must ensure that every person assigned duty as a flight crew member on a relevant aircraft, and who is required to be on flight deck duty for the aircraft, communicates through a boom or throat microphone —
(a)
if the aircraft is a small aeroplane, whenever the aeroplane is flying at an altitude that is below the higher of —
(i)
15,000 ft; or
(ii)
the transition level or altitude; or
(b)
if the aircraft is a helicopter, at all times.