Wind direction indicators
Aircraft normally take off and land into wind, so before every departure and every approach you must know where the wind is coming from. At aerodromes without air traffic services — and whenever the radio fails — ground-based wind direction indicators are your primary source of that information. This lesson covers the windsock and the other visual indicators standardised in ICAO Annex 14, all of which appear regularly in the Air Law exam.
The windsock (wind cone)
ICAO Annex 14 Vol I, §5.1.1 requires that every aerodrome be equipped with at least one wind direction indicator. In practice this is almost always the windsock ("wind cone"): a truncated cone of fabric mounted on a pivoting mast. Wind entering the open mouth inflates the cone, so the sock streams away from the direction the wind is blowing from — to land into wind, you land roughly towards the mouth of the sock.
The windsock also gives a rough indication of wind speed: the stronger the wind, the further the sock rises towards the horizontal. It must be constructed so that it flies fully horizontal at 15 kt (28 km/h) or more; at lower speeds it droops progressively.
| Requirement (Annex 14, §5.1.1) | Detail |
|---|---|
| Number | At least one per aerodrome |
| Visibility | Visible from aircraft in flight, while taxiing and on the apron |
| Siting | Clear of obstructions that would disturb the airflow |
| Illumination | Required if the aerodrome is used at night |
| Length | At least 3.6 m |
| Mouth diameter | At least 0.9 m |
| Behaviour | Clearly indicates wind direction; fully extended at ≥ 15 kt (28 km/h) |
| Colour | Orange/white striped or solid orange |
Location and marking
The windsock is often placed on or near the signal area (signal square), but this is not mandatory; larger aerodromes frequently install additional windsocks near the runway ends so that pilots can read the local wind on short final. The position of a windsock is marked by a white circle of 15 m diameter around its base — particularly useful for spotting it on grass aerodromes.
Other direction indicators
Two further ground devices indicate the direction in use rather than the wind itself:
- Landing direction indicator "T" (landing T): a white or orange "T" displayed on the signal area. Its longitudinal axis shows the landing and take-off direction: landings are made along the shaft of the T towards the cross-arm.
- Tetrahedron: a three-sided, pyramid-shaped body that pivots freely; its apex points in the landing direction.
Remember the distinction: the windsock shows the actual wind, while the landing T shows the direction designated for landing and take-off — at aerodromes with a preferred runway these can differ.
Europe and Germany
In the EU, aerodrome design requirements are applied through Regulation (EU) No 139/2014 (Part-ADR) and the certification specifications CS-ADR-DSN (wind direction indicator: Subpart M). The technical minima are identical to ICAO Annex 14. On German aerodromes the windsock is the standard device; the landing T and the tetrahedron are rare. Illumination is required at aerodromes approved for night operations; details for each aerodrome are published in the AIP VFR Germany (DFS).
Exam essentials
- Every aerodrome must have at least one wind direction indicator (ICAO Annex 14 Vol I, §5.1.1).
- The windsock is a fabric truncated cone at least 3.6 m long with a mouth diameter of at least 0.9 m.
- The windsock flies fully horizontal at wind speeds of 15 kt (28 km/h) or more.
- The sock streams away from the direction the wind blows from; landing is made approximately towards the mouth of the sock.
- The windsock's location is marked by a white circle of 15 m diameter.
- The windsock must be illuminated at aerodromes used for night operations.
- The landing T indicates the landing/take-off direction along its shaft towards the cross-arm; the tetrahedron's apex points in the landing direction.