UA.I.B.K24: Civil twilight operations.

ACS Area I — Regulations Task B: Operating Rules References: 14 CFRCode of Federal RegulationsCloseThe federal rulebook where Part 107, Part 89, Part 48, and other aviation rules live. parts 47, 48, 89, and 107, subpart B; ACAdvisory CircularCloseFAA guidance that explains acceptable ways to comply with rules or understand FAA procedures. 107-2; FAAFederal Aviation AdministrationCloseThe U.S. aviation regulator responsible for Part 107 rules, airspace, and pilot certification processes.-H-8083-25; FAAFederal Aviation AdministrationCloseThe U.S. aviation regulator responsible for Part 107 rules, airspace, and pilot certification processes.-G-8082-22

Key Concepts

What “Civil Twilight” Means and Why It Matters

For Part 107, “night” is the time between the end of evening civil twilight and the beginning of morning civil twilight, as defined in § 1.1 and published in The Air Almanac, converted to local time. In the continental United States, evening civil twilight runs from sunset until 30 minutes after sunset, and morning civil twilight runs from 30 minutes before sunrise until sunrise. In Alaska, the definition of civil twilight differs and is described in The Air Almanac. The Air Almanac provides tables to determine sunrise/sunset at various latitudes, and these data can also be obtained from the U.S. Naval Observatory; be sure to convert to local time for your operation. Practically, civil twilight is the buffer on both sides of night; staying within it means you are not operating at “night” under § 1.1, but you must meet the civil twilight equipment requirement detailed below. If you continue beyond the end of evening civil twilight, you have entered night; if you begin before the start of morning civil twilight, you are still operating at night. Precision in timing is essential for compliance and for exam questions that probe your understanding of these boundaries. ^[1]

Key takeaways for timing:

• Continental U.S.: civil twilight = sunset to 30 minutes after sunset, and 30 minutes before sunrise to sunrise. ^[1]
• Outside the continental U.S. (e.g., Alaska): consult The Air Almanac for the applicable civil twilight definition and timing. ^[1]
• All times from The Air Almanac must be converted to local time. ^[1]

Required Equipment: Anti-Collision Lighting

When small UASSmall Unmanned Aircraft SystemCloseA small drone plus the control and communication links used to operate it. operations occur during civil twilight, the aircraft must be equipped with anti-collision lighting visible for at least 3 statute miles. This visibility requirement is specific and testable; verify manufacturer specifications and conduct a preflight check to ensure the lights are functional and bright enough to meet the 3 statute mile visibility standard. If your lights do not meet that visibility, you are not compliant for civil twilight operations. ^[1]

Practical implications:

• Install lighting rated for at least 3 statute miles visibility; confirm performance after installation.
• Verify lights are operational before launch and monitor them during flight; low battery power can reduce brightness.
• If your aircraft lacks compliant lighting, delay the operation until full daylight or add compliant lights before flying during civil twilight. ^[1]

Planning and Compliance Tips for Test and Field

• Determine the boundary times. Use The Air Almanac (or Naval Observatory data based on The Air Almanac) to obtain official sunrise/sunset for your exact location and date, then apply the civil twilight offsets and convert to local time. Document these times in your preflight planning. ^[1]
• Build a timing buffer. End flight operations before the close of evening civil twilight if you lack the required lighting, and do not launch before the start of morning civil twilight unless you are prepared to meet night requirements beyond the scope of this section. ^[1]
• Consider latitude and season. At higher latitudes and certain seasons, civil twilight periods vary significantly; in Alaska, the definition itself differs and must be obtained from The Air Almanac. Expect exam questions that check whether you know to consult The Air Almanac for Alaska and to convert to local time. ^[1]
• Treat lighting as a go/no-go item. During preflight, confirm anti-collision lighting visibility and mounting security. If uncertain about meeting the “visible for at least 3 statute miles” requirement, do not conduct civil twilight operations. ^[1]
• Recordkeeping mindset. While not a separate regulatory mandate here, maintaining a log of civil twilight times used, lighting checks, and operational decisions supports sound aeronautical decision-making and can help you defend your planning if questioned. ^[1]

Exam focus points:

• Know the exact civil twilight windows in the continental U.S.: 30 minutes after sunset and 30 minutes before sunrise. ^[1]
• Understand that “night” under § 1.1 begins after evening civil twilight ends and ends before morning civil twilight begins. ^[1]
• Memorize the anti-collision lighting requirement: visible for at least 3 statute miles during civil twilight operations. ^[1]
• Remember that Alaska’s civil twilight definition differs; the authoritative source is The Air Almanac, with conversion to local time. ^[1]

By anchoring your planning to The Air Almanac times and ensuring compliant lighting, you will meet the core civil twilight requirements emphasized on the Part 107 exam and in day-to-day flight operations. ^[1]