THE DARK SIDE OF NIGHT

We talk about “day VFR” and make other references to daytime flight, but curiously the FAA does not illuminate us as to what “day” means. But to talk about “day VFR” or whatever implies that there is something other than day. We could call it “night”, but there is a dark side to doing that, it becomes confusing because there are different flavors of night in the regulations. It’s almost better to invent a new term, “non-day”.

The FAA does provide an official definition of “night”. From FAR Part 1.1 "General Definitions":

"Night" means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac, converted to local time.

Further definitions are found in the Pilot/Controller Glossary:

NIGHT

The time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac, converted to local time. (See ICAO term Night)

NIGHT [ICAO]

The hours between the end of evening civil twilight and the beginning of morning civil twilight or such other period between sunset and sunrise as may be specified by the appropriate authority.

Note: Civil twilight ends in the evening when the center of the sun's disk is 6 degrees below the horizon and begins in the morning when the center of the sun's disk is 6 degrees below the horizon.

These definitions need some examination. First, there is the term “civil twilight”. There is probably more than you want to know on this subject at

http://aa.usno.navy.mil/faq/docs/RST_defs.html#top ,

including definitions of civil, nautical, and astronomical twilight. There one finds the following on civil twilight:

Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities. Complete darkness, however, ends sometime prior to the beginning of morning civil twilight and begins sometime after the end of evening civil twilight.

Civil twilight begins/ends about 25-35 minutes on the dark side of sunrise/sunset, depending on time of year and latitude. For practical purposes we say a half hour.

Times of sunrise/sunset, civil twilight, and other events can be found for any date and place by going to http://aa.usno.navy.mil/data/docs/RS_OneDay.html .

The next element of the FAA definition is the reference to the American Air Almanac. No such publication exists today and for some reason the FAA refuses to change the definition. As described in http://aa.usno.navy.mil/about/staff/docs/history.html , “The American Air Almanac” was renamed in 1953 as the “The Air Almanac”, which continues to be published and is available from the Government Printing Office. See http://aa.usno.navy.mil/publications/docs/almanacs.html .

Going beyond definitions, we now examine other FAR references to “non-day”. We will look at those things that are different from official night, and will not include numerous references to night such as things like “so many hours of night flight” required for a certificate or rating. In the absence of any language to the contrary, any reference to night is assumed to be referring to FAR Part 1 definition of night.

§61.57 Recent flight experience: Pilot in command.

(b) Night takeoff and landing experience. (1) Except as provided in paragraph (e) of this section, no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and --

§91.157 Special VFR weather minimums.

(b) Special VFR operations may only be conducted –

(4) Except for helicopters, between sunrise and sunset (or in Alaska, when the sun is 6 degrees or more below the horizon) unless --

(i) The person being granted the ATC clearance meets the applicable requirements for instrument flight under part 61 of this chapter; and

(ii) The aircraft is equipped as required in §91.205(d).

§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

The following are other FAR references to night that impose requirements that are different from day. These refer to official night as defined in FAR part 1.

§91.151 Fuel requirements for flight in VFR conditions.

(a) No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed --

(1) During the day, to fly after that for at least 30 minutes; or

(2) At night, to fly after that for at least 45 minutes.

§91.155 Basic VFR weather minimums.

Day and night Class G airspace rules for visibility and cloud clearance.

§91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.

Day VFR, Night VFR, Day IFR, Night IFR instrument and equipment requirements.