Definition
A white light displayed on a seaplane or airship at night while it is moored or at anchor on the water, used to make the aircraft visible to other vessels and aircraft. The light must be visible from all directions and is required by regulation whenever the aircraft is anchored or moored in a location where other traffic may pass.
Plain English
A white light shown on a seaplane or airship at night when it is parked on the water, so other boats and aircraft can see it and avoid hitting it.
Context Anchor
Seen in seaplane operations, especially when an aircraft is left on the water overnight or during hours of darkness.
Derivation
The term is borrowed directly from maritime use. Boats at anchor have long been required to show a white 'anchor light' at night so passing vessels can see them. Seaplanes adopted the same term and the same idea because they share the water with boats.
Why Pilots Care
Prevents collisions by making the stationary aircraft visible to other vessels and aircraft on the water after dark.
Intuition Check
An anchor light is not a light used while flying. It marks a stationary aircraft on the water, much like a boat showing that it is anchored.
Example Sentence 1
Before leaving the seaplane on its mooring for the night, the pilot switched on the anchor light.
Example Sentence 2
Regulations require the anchor light to remain illuminated whenever the aircraft is moored on the water after sunset.