The period between the end of evening civil twilight and the beginning of morning civil twilight, as defined by the National Weather Service, is crucial for aviation operations. Civil twilight ends when the sun is 6 degrees below the horizon in the evening and begins when the sun is 6 degrees below the horizon in the morning. This specific temporal measurement dictates certain operational requirements and pilot qualifications.
Adherence to this temporal delineation ensures safety by mandating increased visibility requirements and specific training for pilots operating during reduced ambient light conditions. The adoption of this standard reflects a historical evolution in aviation safety practices, born from experiences and technological advancements aiming to mitigate the risks associated with low-light flight. It directly impacts procedures related to aircraft lighting, instrument requirements, and pilot currency.