Flight Redemptions

What is ECET in Aviation? (End Of Civil Evening Twilight)

Updated: February 22, 2024

The Importance of Understanding the End of Civil Evening Twilight (ECET) in Aviation

Aviation is a complex and highly regulated industry that relies on precise calculations and strict adherence to guidelines and procedures. One important aspect of aviation is knowing the different phases of twilight, including the end of civil evening twilight (ECET). Understanding ECET is crucial for pilots, air traffic controllers, and aviation enthusiasts alike, as it plays a significant role in determining visibility, flight operations, and safety during the transition from daylight to darkness.

What is the End of Civil Evening Twilight (ECET)?

The end of civil evening twilight (ECET) is defined as the moment when the sun is 6 degrees below the horizon in the evening. At this point, the sky is still illuminated, but it becomes progressively darker. The exact time of ECET depends on various factors, such as the observer's location, the time of year, and the weather conditions.

ECET is an essential concept in aviation because it marks the beginning of night operations and affects flight planning, airport operations, and the visibility of navigational aids. It is also a crucial factor in determining when pilots need to turn on their aircraft's navigation and anti-collision lights.

The Significance of ECET in Aviation

1. Flight Planning and Visibility:
When planning a flight, pilots need to consider the visibility conditions during the entire journey. ECET serves as a reference point for pilots to determine when daylight is no longer sufficient for visual flight, and they need to rely solely on instrument flight rules (IFR). This is particularly important for longer flights or when flying in areas with limited ground lighting.
During ECET and beyond, the visibility begins to decrease, making it more challenging for pilots to see and identify landmarks, other aircraft, and potential hazards. Understanding the timing of ECET helps pilots make informed decisions regarding flight routes, altitudes, and the need for additional equipment like night vision goggles.

2. Airport Operations and Lighting:
ECET also has implications for airport operations, especially in terms of lighting requirements. As twilight fades into darkness, airports need to ensure that their lighting systems are activated to maintain safe operating conditions. This includes turning on runway lights, taxiway lights, and other visual aids to guide pilots during takeoff, landing, and taxiing.
By knowing the timing of ECET, airport authorities can effectively schedule the activation of their lighting systems, ensuring a smooth transition from daylight to nighttime operations. This helps pilots navigate the airport environment with confidence, even when visibility is reduced.

3. Aviation Regulations and Safety:
The Federal Aviation Administration (FAA) and other aviation regulatory bodies have established specific guidelines and regulations related to ECET. These regulations are in place to ensure the safety of flight operations during the transition from daylight to darkness.
For example, the FAA requires that pilots turn on their aircraft's navigation lights and anti-collision lights from sunset to sunrise, or during the period from ECET to the beginning of morning civil twilight. This helps enhance aircraft visibility and allows other pilots and air traffic controllers to easily spot and identify aircraft.
By adhering to these regulations and understanding the significance of ECET, pilots contribute to the overall safety of the aviation system.


The end of civil evening twilight (ECET) is a critical concept in aviation that affects flight planning, airport operations, and overall safety. Pilots must consider ECET when determining visibility conditions, activating lighting systems, and complying with aviation regulations. By understanding and respecting the importance of ECET, pilots can ensure safer and more efficient flight operations.


FAA Advisory Circular AC 150/5345-46G: Specification for Runway and Taxiway Light Fixtures
Federal Aviation Administration (FAA)

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