Text in force at 27-51: from 27-2, effective 25 Feb 1968.
(a) Each riding light required for water operation must be installed so that it can--
[(1) Show a white light for at least two nautical miles at night under clear atmospheric conditions; and]
(2) Show a maximum practicable unbroken light with the rotorcraft on the water.
(b) Externally hung lights may be used.
33 FR 964 · Source