AIM 4-3-23. Use of Aircraft Lights a. Aircraft position lights are required to be lighted on aircraft operated on the surface and in flight from sunset to sunrise. In addition, aircraft equipped with an anti-collision light system are required to operate that light system during all types of operations (day and night).
Doesn't this imply that anti-collision lights are required to be on during the day? This is obviously not the practice?
Anti-collision lights are required for day and night as specified in the AIM. There's an exception to turn them off if it interferes with the pilot's visibility (e.g. while in the clouds the strobes can be distracting).
This is obviously not the practice?
This is the practice.
Anti collision lights are beacons and strobes. Normally, strobes are avoided when on the ground, except when taking the active.
Navigation or position lights are normally not run during the day, but on larger aircraft they are, and their intensity is greater. The position lights on most planes are silvered lamps, and are quite pricey (~$40 US each when bought in quantity last I recall).
Generally, on light aircraft, best practice by day is to turn on the beacon prior to engine start, and leave it on until shutdown. Nav lights are run during "dark" periods which includes adverse weather. In bright sunlight, they offer little benefit, and operations I am familiar with don't run them.
On heavier aircraft, including biz jets, the standard practice changes, and the beacon comes on with nav lights at startup, and normally those lights run until shutdown. When on a busy ramp at night, it is common practice to leave nav lights on to help bring attention to the wings and tail, even though the engines are off, and the aircraft may be stationary.
While you may not see it at an FBO (as their ramps are well lit, and they don't always have access to the aircraft interior), many freight ops and corporate flight departments will turn on the nav lights when tugging an aircraft on the ramp at night.
Many companies have lighting policies in their procedures which may go beyond this.
14 CFR 91.209 provides general guidance.
§ 91.209 Aircraft lights.
No person may:
(a) During the period from sunset to sunrise (or, in Alaska, during the period a prominent unlighted object cannot be seen from a distance of 3 statute miles or the sun is more than 6 degrees below the horizon) -
(1) Operate an aircraft unless it has lighted position lights;
(2) Park or move an aircraft in, or in dangerous proximity to, a night flight operations area of an airport unless the aircraft -
(i) Is clearly illuminated;
(ii) Has lighted position lights; or
(iii) is in an area that is marked by obstruction lights;
(3) Anchor an aircraft unless the aircraft -
(i) Has lighted anchor lights; or
(ii) Is in an area where anchor lights are not required on vessels; or
(b) Operate an aircraft that is equipped with an anticollision light system, unless it has lighted anticollision lights. However, the anticollision lights need not be lighted when the pilot-in-command determines that, because of operating conditions, it would be in the interest of safety to turn the lights off.
Simplistic, but common practice...
Nav (aka 'Position') lights (low power red/green/white at the extremities of the aircraft... on when the aircraft is powered, to show it's liable to do something.
Anti-Collision (flashing/rotating red light, definitely on top of the aircraft, optionally also below the aircraft)... on when the engines are running, or just before. Warns people to stay away - ground personnel will not approach the aircraft while the red lights are flashing. (The rotating type are often switched off when flying in clouds to avoid visual disorientation.)
Strobe lights (high power, short burst, flashing white on the wingtips)... on in flight, and shortly before getting onto the runway. NOT used in general on the ground due to their high power (think pro-camera flash-gun, it's the same technology) possibly affecting other pilots' vision.
Taxi lights (low power "headlamps")... used when.... taxiing . (For some people, only when taxiing at night.)
Landing lights (high power "headlamps")... go on when "Cleared Takeoff" is received, or on entering the runway. Go off sometime after takeoff (gear up? 10,000ft? depending on operator). Are switched back on again (descending thru 10,000ft, gear down? cleared to land?) before landing.
