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66-402: Dusk occurs at the darkest stage of twilight , or at the very end of astronomical twilight after sunset and just before nightfall. At predusk , during early to intermediate stages of twilight, enough light in the sky under clear conditions may occur to read outdoors without artificial illumination ; however, at the end of civil twilight (when Earth rotates to a point at which the center of

132-575: A Part 91 Operator . These are the regulations that define the operation of small non-commercial aircraft within the United States , however, many other countries defer to these rules. These rules set conditions, such as weather, under which the aircraft may operate. This regulation states that the pilot-in-command is the party directly responsible for, and is the final authority as to, an aircraft being operated. Additionally, this regulation states that in an emergency requiring immediate action,

198-620: A Part 135 certificated airline (owned by the same parent company). This essentially allowed them to function as a scheduled air carrier (typically under Part 121 rules) while adhering to the less stringent Part 135 regulations. This enabled JSX to operate from fixed-based operator terminals, offering a more exclusive, private jet -like experience for their customers. Other air carriers, including Advanced Air , Contour Airlines and Southern Airways Express , have also adopted similar strategies using Part 380. This approach allows them to offer more economical service to smaller cities participating in

264-543: A boon from Brahma that he could not be killed during day or night, neither by human nor animal, neither inside his house nor outside. Vishnu appeared in a half-man half-lion form (neither human nor animal), and ended Hiranyakashipu's life at twilight (neither day nor night) while he was placed in the threshold of his house (neither inside nor outside). Twilight is important in Islam as it determines when certain universally obligatory prayers are to be recited. Morning twilight

330-569: A defensive position. Astronomical twilight is defined as when the geometric center of the Sun is between 18° and 12° below the horizon. During astronomical twilight, the sky is dark enough to permit astronomical observation of point sources of light such as stars , except in regions with more intense skyglow due to light pollution , moonlight , auroras , and other sources of light. Some critical observations, such as of faint diffuse items such as nebulae and galaxies , may require observation beyond

396-409: A large number of regulations to ensure airworthiness in areas such as structural loads, airframe, performance, stability, controllability, and safety mechanisms, how the seats must be constructed, oxygen and air pressurization systems, fire prevention, escape hatches, flight management procedures, flight control communications, emergency landing procedures, and other limitations, as well as testing of all

462-404: A lower angle. The observer's earthly location will pass through the various twilight zones less directly, taking more time. Within the polar circles , twenty-four-hour daylight is encountered in summer, and in regions very close to the poles, twilight can last for weeks on the winter side of the equinoxes . Outside the polar circles, where the angular distance from the polar circle is less than

528-476: A pilot to serve as first officer on a Part 135 flight and pilots are not subject to a mandatory retirement age. Additionally, Part 135 operators have lower TSA screening requirements for passengers. Part 135 operators may not sell individual seats on charter flights. Applicants for a Part 135 certificate must have exclusive use of at least one aircraft. Part 141 is a more structured method for pilot training, based on FAA syllabus and other standards. Part 21

594-415: A polar night: between about 72°34' and 78°34' north or south. Solar noon at astronomical twilight during a polar night: between about 78°34' and 84°34' north or south. Solar noon at night during a polar night: between approximately 84°34' and exactly 90° north or south. At latitudes greater than 81°25' North or South, as the Sun's angular elevation difference is less than 18 degrees, twilight can last for

660-459: A revised Part 23 ruling went into effect, changing the aircraft classifications. The new passenger classifications are: Level 1, seating for 0 to 1 passenger; Level 2, 2 to 6; Level 3, 7 to 9; Level 4, 10 to 19. Speed classifications are: low speed, Vc or Vmo equal to or less than 250 knots CAS and equal to or less than Mmo 0.6 Mach; high speed, Vc or Vmo greater than 250 knots CAS and Mmo greater than 0.6 Mach. Prior to August 30, 2017, Part 23 had

726-433: Is a night with only civil twilight which lasts from sunset to sunrise. At the winter solstice within the polar circle, twilight can extend through solar noon at latitudes below 72.561° (72°33′43″) for civil twilight, 78.561° (78°33′43″) for nautical twilight, and 84.561° (84°33′43″) for astronomical twilight. Twilight on Mars is longer than on Earth, lasting for up to two hours before sunrise or after sunset. Dust high in

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792-554: Is certification for flight crewmembers other than pilots; such as flight engineers and flight navigators. Part 65 is certification for airmen other than flight crewmembers; such as Air Traffic Control Tower Operators, Aircraft Dispatchers, Mechanics, Repairmen and Parachute Riggers. Part 91 is general operating rules for all aircraft. General aviation flights are conducted under this part. Part 91, Subpart (K) prescribes operating rules for fractional ownership programs. Part 107 (FAA sUAS Part 107) specifies regulations to fly under

858-536: Is certification procedures for products and parts. Part 39 are airworthiness directives. Part 43 is maintenance, preventive maintenance, rebuilding, and alteration. Part 145 contains the rules a certificated repair station must follow as well as any person who holds, or is required to hold, a repair station certificate issued under this part. Part 380 governs public charter operators. These companies arrange flights on certified airlines (Part 121 or 135) but then sell individual seats on those flights directly to

924-534: Is on June 21st , while the summer solstice in the Southern Hemisphere is on December 21st . In Arctic and Antarctic latitudes in wintertime, the polar night only rarely produces complete darkness for 24 hours each day. This can occur only at locations within about 5.5 degrees of latitude of the Pole, and there only on dates close to the winter solstice . At all other latitudes and dates,

990-684: Is organized into six subparts, to specify design criteria for each of For example, Part 25, Subpart D has section headings for Most of the Federal Aviation Regulations, including Part 25, commenced on February 1, 1965. Prior to that date, airworthiness standards for airplanes in the transport category were promulgated in Part 4b of the US Civil Air Regulations which was in effect by November 1945. Effective August 27, 1957, Special Civil Air Regulation (SR) 422

1056-451: Is required. Hence, flights are often referred to as Part XX operations , to specify which one of the different sets of rules applies in a particular case. Also, flight schools will often designate themselves as Part 61 or Part 141 to distinguish between different levels of training and different study programs they could offer to the students. Part 61 is certification for all pilots, flight instructors, and ground instructors. Part 63

1122-526: Is treated as a safeguard against encroachment upon either. It can be considered a liminal time. For example, the twilight of Friday is reckoned as Sabbath eve, and that of Saturday as Sabbath day; and the same rule applies to festival days. Federal Aviation Regulations The Federal Aviation Regulations ( FARs ) are rules prescribed by the Federal Aviation Administration (FAA) governing all aviation activities in

1188-488: Is when morning prayers ( Fajr ) are done, while evening twilight is the time for evening prayers ( Maghrib prayer ). Also during Ramadhan, the time for suhoor (morning meal before fasting) ends at morning twilight, while fasting ends after sunset. There is also an important discussion in Islamic jurisprudence between "true dawn" and " false dawn ". In Judaism, twilight is considered neither day nor night; consequently it

1254-534: The 2004 election ). TFRs are deeply unpopular with pilots in the general aviation sector. Presidential TFRs are nearly 70 miles in diameter, and frequently close off not only the airport Air Force One is using but nearby airports as well. Others, including the Transportation Security Administration , argue that they are necessary for national security. TFRs can also be instituted for special military operations, such as with

1320-488: The 2023 Chinese balloon incident , where the FAA put into place one of the largest airspace restrictions in U.S. history, with an area approximately twice the size of Massachusetts and more than five times the restricted airspace surrounding Washington, D.C. The responsibility for screening requests for TFR and for subsequent granting or denying them, lies with the FAA's Office of System Operations Security. Section 91.185 of

1386-554: The Electronic Code of Federal Regulations (e-CFR). The table of contents, as reflected in the e-CFR updated December 20, 2018: Each title of the CFR is organized into sections, called parts . Each part deals with a specific type of activity. For example, 14 CFR Part 141 contains rules for pilot training schools. The sections most relevant to aircraft pilots and AMTs (Aviation Maintenance Technicians) are listed below. Many of

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1452-654: The September 11, 2001 attacks , most TFRs were in the interest of safety to flying aircraft with occasional small restrictions for Presidential movements. Since 9/11, TFRs have been routinely used to restrict airspace for 30 nautical miles around the President, with a 10-nautical-mile (18.5 km) radius no-fly zone for non-scheduled flights. They are also available to other high-profile figures such as presidential and vice-presidential candidates (though not all do so, as Senator John Kerry , who did not ask for any TFR during

1518-473: The Sun 's disk is 6° below the local horizon ), such lighting is required to read outside. The term dusk usually refers to astronomical dusk , or the darkest part of twilight before night begins. The time of dusk is the moment at the very end of astronomical twilight, just before the minimum brightness of the night sky sets in, or may be thought of as the darkest part of evening twilight . However, technically,

1584-638: The United States . The FARs comprise Title 14 of the Code of Federal Regulations ( 14 CFR ). A wide variety of activities are regulated, such as aircraft design and maintenance, typical airline flights, pilot training activities, hot-air ballooning , lighter-than-air aircraft , human-made structure heights, obstruction lighting and marking, model rocket launches, commercial space operations, model aircraft operations, Unmanned Aircraft Systems (UAS) and kite flying. The rules are designed to promote safe aviation , protecting pilots, flight attendants, passengers and

1650-469: The DC-8, DC-9, and B-727, were originally certified under SR 422B. SR 422B was recodified with minor changes to 14 CFR part 25, which became effective February 1965. This part contains airworthiness standards for rotorcraft in the normal category. Rotorcraft up to 7,000 lb Maximum takeoff weight and 9 or fewer passengers are type certified in this part. Examples of rotorcraft certified in this part are

1716-529: The Earth, including the entire United Kingdom and other countries in northern Europe and even parts of central Europe . This also occurs in the Southern Hemisphere, but occurs on December 21. This type of twilight also occurs between one day and the next at latitudes within the polar circles shortly before and shortly after the period of midnight sun. The summer solstice in the Northern Hemisphere

1782-583: The FARs are designed to regulate certification of pilots, schools, or aircraft rather than the operation of airplanes. Once an airplane design is certified using some parts of these regulations, it is certified regardless of whether the regulations change in the future. For that reason, newer planes are certified using newer versions of the FARs, and in many aspects may be thus considered safer designs. The FARs have tens of thousands of separate sections, many used by large numbers of researchers on any given day. A few of

1848-563: The Federal Aviation Restrictions deals with loss of radio communications while in flight . If a loss of radio communications were to be encountered during VFR conditions, or if VFR conditions are encountered after loss of communication with the ground and other aircraft, the pilot of the aircraft shall continue the flight under VFR and land as soon as practicable. If, however, the failure occurs in IFR conditions and/or

1914-568: The Robinson R44, Schweizer 300 and the Bell 429 . This part contains airworthiness standards for rotorcraft in the transport category . Rotorcraft with more than 7,000 lb (3,200 kg) maximum takeoff weight and 10 or more passengers are type certified in this part. Rotorcraft with more than 20,000 lb (9,100 kg) maximum takeoff weight must be certified to additional Category A standards defined in this part. Part 91 defines

1980-585: The Small UAS Rule, or small unmanned aircraft systems in the National Airspace System (NAS). Small unmanned aircraft systems (sUAS) are those that weigh less than 55 pounds. Part 117 specifies flight and duty-time limitations and rest requirements for flightcrew members. Part 121 defines regularly scheduled air carriers. These are airlines who operate scheduled flights carrying either cargo or more than nine passengers. Among

2046-464: The Sun is below the horizon. Examples include when drivers of automobiles must turn on their headlights (called lighting-up time in the UK), when hunting is restricted, or when the crime of burglary is to be treated as nighttime burglary, which carries stiffer penalties in some jurisdictions. The period may affect when extra equipment, such as anti-collision lights, is required for aircraft to operate. In

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2112-611: The US Civil Air Regulations. Many well-known types of light airplane, like the Cessna 150 and Piper Cherokee are certified to these older standards, even though they remained in production after 1965. This part contains airworthiness standards for airplanes in the transport category . The Boeing 737 and later types, and Airbus A300 series, are well-known airplane types that were certified according to standards set out in FAR Part 25. Transport category airplanes are either: This Part

2178-635: The US, civil twilight for aviation is defined in Part 1.1 of the Federal Aviation Regulations (FARs) as the time listed in the American Air Almanac. Nautical twilight occurs when the geometric center of the Sun is between 12° and 6° below the horizon. After nautical dusk and before nautical dawn, sailors cannot navigate via the horizon at sea as they cannot clearly see the horizon. At nautical dawn and nautical dusk,

2244-592: The United States Code of Federal Regulations (CFR). Title 14 is the principal set of rules and regulations (sometimes called administrative law ) issued by the Department of Transportation and Federal Aviation Administration , federal agencies of the United States which oversee Aeronautics and Space . This title is available in digital and printed form, and can be referenced online using

2310-471: The VFR conditions are not forthcoming, the pilot should continue under the following conditions: For all pilots, there is an important distinction in the parts that address classes of flight. These parts do not distinguish type of aircraft, but rather type of activity done with the aircraft. Regulations for commuter and commercial aviation are far more intensive than those for general aviation, and specific training

2376-553: The absence of other illumination, during nautical twilight, the human eye may distinguish general outlines of ground objects but cannot participate in detailed outdoor operations. Nautical twilight has military considerations as well. The initialisms BMNT (begin morning nautical twilight, i.e. nautical dawn) and EENT (end evening nautical twilight, i.e. nautical dusk) are used and considered when planning military operations. A military unit may treat BMNT and EENT with heightened security, e.g. by "standing to", for which everyone assumes

2442-496: The absence of shadows and the appearance of objects silhouetted against the lit sky, twilight has long been popular with photographers and painters, who often refer to it as the blue hour , after the French expression l'heure bleue . By analogy with evening twilight, sometimes twilight is used metaphorically to imply that something is losing strength and approaching its end. For example, very old people may be said to be "in

2508-416: The acrobatic and utility categories). The Cessna 177 , Cirrus SR20 and Piper PA-34 Seneca are well-known airplanes types that were certified to standards set out in FAR Part 23. Most of the Federal Aviation Regulations, including Part 23, commenced on February 1, 1965. Prior to that date, airworthiness standards for airplanes in the normal, utility and acrobatic categories were promulgated in Part 3 of

2574-543: The angle which defines twilight (see above), twilight can continue through local midnight near the summer solstice . The precise position of the polar circles, and the regions where twilight can continue through local midnight, varies slightly from year to year with Earth's axial tilt . The lowest latitudes at which the various twilights can continue through local midnight are approximately 60.561° (60°33′43″) for civil twilight, 54.561° (54°33′43″) for nautical twilight and 48.561° (48°33′43″) for astronomical twilight. These are

2640-473: The atmosphere scatters light to the night side of the planet. Similar twilights are seen on Earth following major volcanic eruptions . In Christian practice, " vigil " observances often occur during twilight on the evening before major feast days or holidays. For example, the Easter Vigil is held in the hours of darkness between sunset on Holy Saturday and sunrise on Easter Day – most commonly in

2706-526: The entire 24 hours. This occurs for one day at latitudes near 8°35’ from the Pole and extends up to several weeks the further toward the Pole one goes. This happens both near the North Pole and near the South Pole. The only permanent settlement to experience this condition is Alert, Nunavut , Canada, where it occurs from February 22–26, and again from October 15–19. The duration of twilight depends on

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2772-496: The evening of Holy Saturday or midnight – and is the first celebration of Easter, days traditionally being considered to begin at sunset. Hinduism prescribes the observance of certain practices during twilight, a period generally called sandhya . The period is also called by the poetic form of gōdhūḷi in Sanskrit , literally 'cow dust', referring to the time cows returned from the fields after grazing, kicking up dust in

2838-479: The general public from unnecessary risk. Since 1958, these rules have typically been referred to as "FARs", short for Federal Aviation Regulations. However, another set of regulations (Title 48) is titled "Federal Acquisitions Regulations", and this has led to confusion with the use of the acronym "FAR". Therefore, the FAA began to refer to specific regulations by the term "14 CFR part XX". FAA Order 1320.46C (Advisory Circular System) section 10 (Using references in

2904-400: The horizon while the brightest stars and planets can appear. As observed from the Earth (see apparent magnitude ), sky-gazers know Venus , the brightest planet, as the "morning star" or "evening star" because they can see it during civil twilight. Civil twilight statutes typically denote a fixed period after sunset or before sunrise (most commonly 20–30 minutes) rather than how many degrees

2970-517: The horizon), nautical twilight, and astronomical twilight (farthest from the horizon). Civil twilight is the time when the geometric center of the Sun is between the horizon and 6° below the horizon. Civil twilight is the period when enough natural light remains so that artificial light in towns and cities is not needed. In the United States' military, the initialisms BMCT ( begin morning civil twilight , i.e., civil dawn) and EECT ( end evening civil twilight , i.e., civil dusk) are used to refer to

3036-512: The human eye finds it difficult, if not impossible, to discern traces of illumination near the sunset or sunrise point of the horizon ( first light after nautical dawn but before civil dawn and nightfall after civil dusk but before nautical dusk). Sailors can take reliable star sightings of well-known stars, during the stage of nautical twilight when they can distinguish a visible horizon for reference (i.e. after astronomic dawn or before astronomic dusk). Under good atmospheric conditions with

3102-431: The largest cities of their respective countries where the various twilights can continue through local solar midnight: Although Helsinki, Oslo, Stockholm, Tallinn, and Saint Petersburg also enter into nautical twilight after sunset, they do have noticeably lighter skies at night during the summer solstice than other locations mentioned in their category above, because they do not go far into nautical twilight. A white night

3168-413: The latitude and the time of the year. The apparent travel of the Sun occurs at the rate of 15 degrees per hour (360° per day), but sunrise and sunset happen typically at oblique angles to the horizon and the actual duration of any twilight period will be a function of that angle, being longer for more oblique angles. This angle of the Sun's motion with respect to the horizon changes with latitude as well as

3234-641: The limit of astronomical twilight. Theoretically, the faintest stars detectable by the naked eye (those of approximately the sixth magnitude) will become visible in the evening at astronomical dusk, and become invisible at astronomical dawn . Observers within about 48°34' of the Equator can view twilight twice each day on every date of the year between astronomical dawn , nautical dawn, or civil dawn, and sunrise as well as between sunset and civil dusk, nautical dusk, or astronomical dusk. This also occurs for most observers at higher latitudes on many dates throughout

3300-547: The many Part 121 rules, pilots must have 1,500 of flight time and must retire by age 65. Part 133 is external load (helicopter) operations. Part 135 defines commuter and charter-type air carriers. These airlines can fly scheduled operations with aircraft with up to nine passengers (commuter flights), or they can fly on-demand, unscheduled air service for freight or with up to 30 passengers (charter flights). The Part 135 rules for pilots are less onerous, compared to Part 121: only 250 hours of flight time are required for

3366-601: The month of the autumnal equinox and the month of vernal equinox between astronomical dawn, nautical dawn, or civil dawn, and sunrise as well as between sunset and civil dusk, nautical dusk, or astronomical dusk, i.e., from September 1 to March 31 of the following year in the Northern Hemisphere and from March 1 to September 30 in the Southern Hemisphere . The nighttime/twilight boundary solar midnight's latitude varies depending on

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3432-485: The month: At latitudes greater than about 48°34' North or South, on dates near the summer solstice ( June 21 in the Northern Hemisphere or December 21 in the Southern Hemisphere), twilight can last from sunset to sunrise, since the Sun does not sink more than 18 degrees below the horizon, so complete darkness does not occur even at solar midnight. These latitudes include many densely populated regions of

3498-593: The pilot-in-command may deviate from any regulation contained within Part 91 to the extent required to handle the emergency. The pertinent sections of the FAR (14 CFR Sections 91.137, 91.138, 91.139, 91.141, 91.143, 91.145, 99.7) describe temporary flight restrictions ( TFR ). A TFR is a geographically-limited, short-term, airspace restriction, typically in the United States . Temporary flight restrictions often encompass major sporting events, natural disaster areas, air shows, space launches, and Presidential movements. Before

3564-504: The polar night includes a daily period of twilight, when the Sun is not far below the horizon. Around winter solstice, when the solar declination changes slowly, complete darkness lasts several weeks at the Pole itself, e.g., from May 11 to July 31 at Amundsen–Scott South Pole Station . North Pole has the experience of this from November 13 to January 29. Solar noon at civil twilight during a polar night: between about 67°24' and 72°34' north or south . Solar noon at nautical twilight during

3630-573: The poles, civil twilight can be as long as 2–3 weeks. In the Arctic and Antarctic regions, twilight (if there is any) can last for several hours. There is no astronomical twilight at the poles near the winter solstice (for about 74 days at the North Pole and about 80 days at the South Pole). As one gets closer to the Arctic and Antarctic circles, the Sun's disk moves toward the observer's horizon at

3696-425: The process. Many rituals, such as Sandhyavandanam and puja , are performed at the twilight hour. Consuming food is not advised during this time. According to some adherents, asuras are regarded to be active during these hours. One of the avatars of Vishnu , Narasimha , is closely associated with the twilight period. According to Hindu scriptures , an asura king, Hiranyakashipu , performed penance and obtained

3762-448: The public. Unlike the airlines they partner with, Part 380 operators don't operate the aircraft themselves. Historically, this business model has been used by tour operators and casinos to offer occasional flights between smaller cities and popular leisure destinations. However, more recently, the Part 380 rules have also seen some creative applications. In 2016, JSX began scheduling flights and selling tickets on flights operated by

3828-721: The regulations particularly relevant to laypersons, to political issues, or of historical interest are listed here. Many other FARs depend on definitions, which are found in Part 1.1 This part prescribes: Part 23 contains airworthiness standards required for issuance and change of type certificates for airplanes in these categories : In 2016 the FAA proposed a new system of performance-based airworthiness standards instead of prescriptive design requirements. The familiar weight and propulsion classifications of small airplane regulations would be replaced by performance and risk-based standards for aircraft weighing less than 19,000 pounds and seating 19 or fewer passengers. On August 30, 2017,

3894-514: The start of morning civil twilight and the end of evening civil twilight, respectively. Civil dawn is preceded by morning nautical twilight and civil dusk is followed by evening nautical twilight. Under clear weather conditions, civil twilight approximates the limit at which solar illumination suffices for the human eye to clearly distinguish terrestrial objects. Enough illumination renders artificial sources unnecessary for most outdoor activities. At civil dawn and at civil dusk, sunlight clearly defines

3960-404: The systems of the aircraft. It also determined special aspects of aircraft performance such as stall speed (e.g., for single engine airplanes – not more than 61 knots), rate of climb (not less than 300 ft/min), take-off speed (not less than 1.2 x V S1 ), and weight of each pilot and passenger (170 lb for airplanes in the normal and commuter categories, and 190 lb for airplanes in

4026-583: The text of an AC) para. h explains " Do not use the acronym "FAR" to refer to FAA's regulations. Neither the Department of Transportation nor the Office of the Federal Register allow us to use "FAR" for our regulations. The Federal Acquisition Regulations apply government-wide and are allowed to use the acronym "FAR." " Title 14 CFR – Aeronautics and Space is one of the fifty titles that make up

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4092-476: The three stages of dusk are as follows: Twilight The lower the Sun is beneath the horizon, the dimmer the sky (other factors such as atmospheric conditions being equal). When the Sun reaches 18° below the horizon, the illumination emanating from the sky is nearly zero, and evening twilight becomes nighttime . When the Sun approaches re-emergence, reaching 18° below the horizon, nighttime becomes morning twilight. Owing to its distinctive quality, primarily

4158-459: The time of year (affecting the angle of the Earth's axis with respect to the Sun). At Greenwich, England (51.5°N), the duration of civil twilight will vary from 33 minutes to 48 minutes, depending on the time of year. At the equator , civil twilight can last as little as 24 minutes. This is true because at low latitudes the Sun's apparent movement is perpendicular to the observer's horizon. But at

4224-440: The twilight of their lives". The collateral adjective for twilight is crepuscular , which may be used to describe the behavior of animals that are most active during this period. Twilight occurs according to the solar elevation angle θ s , which is the position of the geometric center of the Sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (nearest

4290-457: The year, except those around the summer solstice. However, at latitudes closer than 8°35' (between 81°25’ and 90°) to either Pole, the Sun cannot rise above the horizon nor sink more than 18° below it on the same day on any date, so this example of twilight cannot occur because the angular difference between solar noon and solar midnight is less than 17°10’. Observers within 63°26' of the Equator can view twilight twice each day on every date between

4356-695: Was the basis for certification of the first turbine-powered transport airplanes, such as the Boeing 707, the Lockheed Electra, and the Fairchild 27. SR 422A became effective July 2, 1958, and was superseded by SR 422B, effective August 29, 1959. Only a few airplanes were certified under SR 422A, such as the Gulfstream I and the CL-44. First generation turbine-powered transport category airplanes such as

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