How does a windsock glow at night?
A lamp inside the cone lights the fabric from within, so the pilot can read wind direction and strength after dark.
An internally illuminated windsock is a fabric cone on a swivel that points downwind. The wind fills the large end and leaves by the small end, so the cone shows the wind direction, and how far it stands out shows the strength. A lamp inside the cone lights the translucent fabric from within, so the cone can be read at night as it is by day. ICAO Annex 14 recommends that at least one wind direction indicator at an aerodrome used at night is illuminated.
The lamp sits near the frame ring at the large end and is fed by a cable up the mast. Because the cone turns, the lamp is either fixed on the mast head or fed through a slip ring, depending on the make. The glow should be even, so the shape and bands stay readable. At each visit check the lamp, the glow, the fabric and the swivel, because a cone that sticks or hangs limp gives a false reading. An FAA Style I-B internally lighted cone must also carry a backup light source, so one lamp failure does not leave the cone dark. The externally illuminated windsock, lit by lights outside the cone, is a separate entry.
Frequently Asked Questions
Q1What is an internally illuminated windsock?
A windsock with a lamp inside the cone. The lamp lights the fabric from within, so the cone glows at night and the pilot can still read the wind direction and strength, as by day.
Q2How does a windsock show the wind?
The wind fills the large end and leaves by the small end, which makes the cone point downwind. In a light wind it droops; in a strong wind it stands out nearly straight, so how far it stands out shows how strong the wind is.
Q3Why is the lamp inside the cone?
It lights the whole fabric evenly from within, so the full cone shape and its colour bands show against the dark sky, with no separate floodlights needed on or near the mast.
Q4How does power reach a lamp in a cone that turns?
By a cable up the mast. Either the lamp is fixed on the mast head with the cone turning around it, or the feed passes through a slip ring that lets the cone turn without twisting the cable. The arrangement depends on the make.
Q5What should be checked on an internally illuminated windsock?
That the lamp, and any backup lamp, lights at night and the glow is even; that the fabric is clean, not faded or torn; that the cone turns freely on its swivel and fills in a light wind; and that the cable, connections and slip ring are sound. Isolate the supply and use safe access before working at the mast head.
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