Night: The aviation definition of the term Night has a significant Regulatory impact on aviation and worldwide aircraft operations . Many international regulations and standards apply specifically to aviation operations conducted at night or differentiate between operations permitted by day and those permitted at night. In certain circumstances both pilots and the operation of specific aircraft may be restricted to day only operations.
The term Night has different definitions depending where and in what context the term is being used:
FAA (14 CFR 1) 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.
Below is an example of data retrieved from the U.S. Naval Observatory
Astronomical Applications Department (Air Almanac Publisher)
Sun and Moon Data for One Day
The following information is provided for Barrow, North Slope Borough, Alaska (longitude W156.8, latitude N71.3):
Monday 26 January 2009 Alaska Standard Time
Begin civil twilight 10:21 a.m.
Sunrise 12:20 p.m.
Sun transit \ 1:40 p.m.
Sunset 3:00 p.m.
End civil twilight 5:00 p.m.
Tuesday 27 January 2009 Alaska Standard Time
Begin civil twilight 10:17 a.m.
Sunrise 12:11 p.m.
Sun transit 1:40 p.m.
Sunset 3:10 p.m.
End civil twilight 5:05 p.m.
In the above example, Night would start at 5:00 p.m.on Monday and would end at 10:17 a.m on Tuesday
FAA (14 CFR 61.57) Night means in regards to 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”
FAA (14 CFR 91.209) Night means in regards to using navigation lights: (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)—
ICAO – Night means 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 prescribed by the appropriate authority. Note.— Civil twilight ends in the evening when the centre of the sun’s disc is 6 degrees below the horizon and begins in the morning when the centre of the sun’s disc is 6 degrees below the horizon.
UK Air Navigation Order – Night means the time between half an hour after sunset and half an hour before sunrise (both times inclusive), sunset and sunrise being determined at surface level.
Transport Canada provides some guidance on the history and the changes they implemented in 2003 of their definition of Night & Day:
The definitions “day” and “night” in subsection 101.01(1) of the Canadian Aviation Regulations are replaced by the following:
“day” or “daylight” means the time between the beginning of morning civil twilight and the end of evening civil twilight;(jour)
“night” means the time between the end of evening civil twilight and the beginning of morning civil twilight; (nuit)
The Regulations Amending the Canadian Aviation Regulations (Part I) revise the existing definitions of “day” and “night” in section 101.01 Interpretation of Part I General Provisions of the Canadian Aviation Regulations (CARs). Many regulations and standards apply specifically to aviation operations at night or differentiate between operations permitted by day and those permitted at night. Often air operators or pilots holding Canadian aviation documents are restricted to day only operations. Thus, the existence in the CARs of definitions of “day” and of “night” is an important regulatory tool as well as having significant economic implications for the aviation industry.
Prior to these amendments, both definitions relied on a period of one-half hour before sunrise (day) and one-half hour after sunset (night). The intent of the definitions was to include the lighting and visibility conditions of twilight with those of day for aviation operational purposes. They took into account the latitudes and seasons during which the sun neither rises nor sets daily by defining day and night in these places in relation to the centre of the sun’s disc with respect to the horizon. Many of the northern regions of Canada lie in latitudes where, in the spring and fall, the sun rises and sets daily but does so after a lengthy period of twilight. This period, in these locations, can be up to two hours, i.e., much longer than the half-hour allowed for in the aviation-specific definitions of “day” and “night” prior to these amendments. At times and places where the sun does rise and set daily but with a period of twilight at certain seasons which is longer than the half-hour, the previous definition of “night” was unnecessarily restrictive. In these latitudes, at these times, “night” began, with its additional operational restrictions, one half-hour after sunset although the light conditions might have been sufficient for day operations for much longer.
To avoid ambiguity, in English, between the use of “day” to mean daylight conditions and “day” to mean a period of twenty-four hours, the English definition of “day”, when the context refers to daylight conditions, is revised to refer to “day or daylight”. This ambiguity does not exist in French. Therefore, the French definition refers only to “day”. “day or daylight” is defined as “the time between the beginning of morning civil twilight and the end of evening civil twilight”. Since the use of “night” involves no such ambiguity, “night” is defined as “the time between the end of evening civil twilight and the beginning of morning civil twilight”. These changes acknowledge geographical variations in light conditions at different times of year and reduce the daily period during which restrictions related to night operating conditions apply in northern districts.