Definition
A wind direction indicator at non-towered airports, shaped like a four-sided pyramid mounted on a pivot, that swings to point into the wind so arriving pilots can identify the favored landing direction.
Plain English
A large, pyramid-shaped pointer near the runway that turns with the wind. The pointed end shows the direction you should land — you land toward the point, into the wind.
Context Anchor
Seen on the airport surface at some smaller airports, often near other wind and landing-direction indicators.
Derivation
From the Greek 'tetra' (four) and 'hedra' (seat or face), meaning a shape with four faces. The landing aid is named for its four-sided pyramid form.
Why Pilots Care
It gives immediate visual wind information when no tower or ATIS is available, helping pilots select the correct runway and manage crosswind landings safely.
Analogy
Think of it like a big fixed arrow on the airport surface. It does not point to a place; it points the direction aircraft should be traveling when they land.
Intuition Check
Do not read this as only a geometry term. In airport use, “tetrahedron” means a landing-direction marker, and its small end points in the direction of landing.
Example Sentence 1
On downwind, the pilot glanced at the tetrahedron and confirmed it still favored Runway 27.
Example Sentence 2
Before taxiing out, the pilot checked the tetrahedron to confirm the current wind direction.