All craft should have steady lit red on the port (left) side, green on the starboard (right) side, usually on the wingtips for planes and sides of the
fuselage on helicopters and a white light on the rear. These red / green / white lights may not necessarily be visible from the ground. Also, there
should be white strobes on the top and bottom of the fuselage and possibly at the tip of the tail and wings, to draw attention particularly in low
visibility, and possibly red or white rotating or slowly pulsating lights, which are typically turned on during taxiing, landing and departure from
Landing lights (steady white) and other lights (to light the tail number for instance) may also be on, depending on elevation and what type of craft
and what it's doing.
Military craft should follow FAA requirements whenever they are operating in civilian airspace, i.e. not over a military installation.
Many helicopters, particularly law enforcement types, use turbines for power and depending on the actual craft you may only hear the turbines at
edit on 2/11/2012 by abecedarian because: (no reason given)