CAA CAP 168 Windsock Requirements: A Practical Guide for UK Aerodrome Operators
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What CAA CAP 168 is and why it matters
CAA CAP 168 (Civil Aviation Authority Licensing of Aerodromes) is the document UK aerodrome operators use to demonstrate that their site meets the licensing standards set by the UK Civil Aviation Authority. It covers physical characteristics, visual aids, rescue and firefighting, and operational procedures. Within the visual aids section, it sets out specific requirements for wind direction indicators, the formal term for windsocks.
If you operate a licensed aerodrome in the United Kingdom, CAP 168 is not optional reading. It is the framework your inspector will check against. If you procure equipment for a licensed aerodrome, you need to match your specification to CAP 168 before you raise the purchase order.
This guide breaks down what CAP 168 says about windsocks, how to translate that into a procurement specification, and where the common mistakes happen.
CAP 168 windsock requirements in detail
CAP 168 sets out the requirements for the primary wind direction indicator at a licensed aerodrome. The provisions align closely with ICAO Annex 14 (International Civil Aviation Organization, Aerodromes, Volume 1) because the UK CAA adopts ICAO standards with limited national variation.
Number and placement
Every licensed aerodrome must have at least one wind direction indicator. The indicator must be:
- Visible from aircraft in flight, from aircraft on the movement area, and to personnel on the apron.
- Located so it is free from the effects of airflow disturbances caused by nearby buildings or other structures.
- Sited so the windsock and its supporting mast do not present an obstacle to aircraft operations.
For aerodromes operating at night, the wind direction indicator must be illuminated.
Physical specification
CAP 168 specifies the construction of the wind direction indicator itself. The key requirements are:
- Truncated cone shape, made of fabric.
- Minimum length of 3.6 metres (12 feet).
- Minimum diameter at the larger (throat) end of 0.9 metres.
- Minimum diameter at the smaller (trailing) end of 0.3 metres.
- Constructed so it gives a clear indication of wind direction and a general indication of wind speed.
- Coloured to make it conspicuous against the background, using either a single colour (typically orange) or two contrasting colours (typically orange and white in alternating bands).
The 15 knot calibration is the practical benchmark. A correctly constructed windsock should extend fully horizontal in a wind of 15 knots (28 km/h) and indicate lighter winds by partial extension.
Lighting for night operations
Where an aerodrome operates at night, the primary wind direction indicator must be illuminated. Internal illumination is the preferred method because it lights the sock evenly and avoids dazzle. External flood-lighting from a downward-pointing fitting is also acceptable.
Mounting and frangibility
The supporting structure must be frangible. If an aircraft strikes the mast, the mast should break away cleanly to minimise damage. This is a key safety point that procurement specifications often miss.
Specification table: CAP 168 vs Falcon Premium
The table below maps the CAP 168 requirements directly to the Falcon Premium 12FT specification, which is the size most commonly purchased for licensed aerodromes.
| CAP 168 Requirement | Specification | Falcon Premium 12FT |
|---|---|---|
| Shape | Truncated fabric cone | Truncated fabric cone |
| Minimum length | 3.6 m | 3.66 m (12 ft) |
| Minimum throat diameter | 0.9 m | 0.91 m |
| Minimum trailing diameter | 0.3 m | 0.30 m |
| Calibration | Full extension at 15 knots | Full extension at 15 knots |
| Colour | Conspicuous, single or alternating | Orange and white alternating bands, or solid orange |
| Construction | Durable weather-resistant fabric | Marine-grade polyester, double-stitched seams |
| Mounting | Frangible support | Compatible with frangible masts and Falcon Swivel Arm |
| Night operations | Illumination required | Compatible with internally lit and floodlit assemblies |
For aerodromes where the 12FT is not appropriate, for example general aviation strips with shorter sight lines, the Falcon Premium 7FT meets the requirements of smaller unlicensed sites. The 12FT is the right choice for any aerodrome operating under a CAA licence. See the windsock size guide for a fuller breakdown.
How to write a CAP 168-compliant procurement specification
A buyer-facing specification should leave nothing to interpretation. The following structure works for tender documents and internal purchase orders.
1. Reference the standard
Open the specification with the standard you are buying against. For a UK licensed aerodrome:
"The wind direction indicator shall comply with CAA CAP 168, Chapter 6 (Visual Aids), and shall meet the dimensional and construction requirements set out therein."
2. State the size
Specify the length explicitly. A line such as "12-foot windsock" is unambiguous and matches the CAP 168 minimum.
3. State the colour scheme
Either "alternating orange and white bands, five bands total" or "solid orange". Match what your site uses already so replacements remain consistent.
4. Specify the fitting type
Snap-on (also called harness-fitted) windsocks attach to a metal frame and are quick to replace. Lace-on windsocks tie directly to a swivel arm and have no harness. Both meet CAP 168 if correctly sized. See our windsock installation guide for the practical differences.
5. Specify the mounting hardware
If you are buying a complete assembly, include the mast, the swivel arm, and any lighting. If you are buying a replacement sock only, state the diameter of the harness or the length of the lace points so it fits your existing arm.
6. State the lighting requirement
For night-operational sites, state whether you need an internally lit assembly or external floodlighting. This decision affects the type of swivel arm and the wiring specification.
Common compliance mistakes
The aerodromes we supply most often run into the same handful of issues. Most are avoidable at the specification stage.
Undersized socks on licensed sites. A 7FT windsock at a CAA-licensed aerodrome will fail inspection. The 3.6 m minimum is not a guideline, it is a requirement.
Non-frangible mounting. A heavy steel pole bolted into concrete is not frangible. The mast must break away if struck. Specify a frangible coupler or a purpose-built aviation mast.
Wrong calibration. Cheap windsocks made from heavy fabric do not extend fully at 15 knots. They under-read wind speed in the visual indication. CAP 168 implies the 15-knot calibration through the requirement to indicate wind speed accurately.
Faded colours. Sun-bleached orange fades to pink within 18 to 24 months on a cheap polyester windsock. CAP 168 requires the sock to remain conspicuous. Plan a replacement cycle. Our windsock replacement guide covers inspection intervals.
Obstructed sight lines. A windsock placed behind a hangar or downwind of a tree line will not give an accurate reading. Site survey before installation.
How CAP 168 compares to other standards
CAP 168 aligns closely with ICAO Annex 14 because the UK CAA adopts ICAO provisions. The dimensions are identical. The main differences are administrative, around licensing procedures rather than the windsock itself.
FAA AC 150/5345-27F (Federal Aviation Administration, Specification for Wind Cone Assemblies) takes a different approach. The FAA defines two sizes, the Size 1 (8-foot) and the Size 2 (12-foot), and treats the assembly as a unit including the lighting and frangible mount. CAP 168 leaves more flexibility on the mounting and treats the sock and assembly separately.
For a fuller comparison of frameworks, including EASA EU Regulation 139/2014 and HSE COMAH for non-aviation industrial sites, see our windsock compliance standards pillar guide. If your site is industrial rather than aviation, also read aviation versus industrial windsocks.
Procurement, lead times and delivery
Falcon manufactures the Premium range in the United Kingdom. We hold stock of all standard sizes in both orange-and-white banded and solid orange. Lead times for standard items are short.
We ship free worldwide with duties and import taxes covered (DDP). For UK orders this is a standard next-step delivery. For aerodromes outside the UK that purchase against CAP 168 because their operations licence references it, the DDP service means the price you see is the price you pay, with no customs charges on arrival.
Frequently asked questions
What size windsock does CAA CAP 168 require?
CAA CAP 168 requires a minimum length of 3.6 metres (12 feet), a minimum throat diameter of 0.9 metres, and a minimum trailing diameter of 0.3 metres. The Falcon Premium 12FT meets these dimensions.
Does CAP 168 require windsock lighting?
Yes, for aerodromes that operate at night. The primary wind direction indicator must be illuminated. Internal illumination is preferred, but external floodlighting from a downward fitting is acceptable.
What colours are required for a CAP 168 windsock?
The sock must be conspicuous against its background. Solid orange or alternating bands of orange and white are the standard options. Five bands of alternating colour is the most common configuration in the UK.
Is CAP 168 the same as ICAO Annex 14 for windsocks?
The dimensional and construction requirements are effectively the same because the UK CAA adopts ICAO Annex 14 provisions. CAP 168 sits within the UK licensing framework and includes additional procedural detail specific to UK aerodromes.
Does a small general aviation strip need a CAP 168 windsock?
If the site is licensed by the CAA, yes. Unlicensed strips are not bound by CAP 168, but operators often specify to CAP 168 anyway because it is the recognised standard. A 12-foot sock is the safe choice for any site that might seek licensing.
What does "frangible" mean in the mounting requirement?
Frangible means the mast or its coupler will break cleanly if struck by an aircraft, minimising damage. CAP 168 requires frangible mounting because the windsock is sited within or near the movement area.
How often should a CAP 168 windsock be replaced?
Inspect quarterly. Replace when colour has faded, when fabric is torn or thinning, or when the sock no longer extends fully at 15 knots. Typical replacement intervals run from 18 months to 3 years depending on exposure.
The Falcon Premium range
The Falcon Premium is manufactured in the United Kingdom to meet CAA CAP 168, ICAO Annex 14 and EASA EU Regulation 139/2014 aviation standards. The range is available in 4FT, 7FT and 12FT lengths, in snap-on or lace-on fittings, in solid orange or alternating orange and white. All sizes ship free worldwide with duties and taxes covered.
For a CAA-licensed aerodrome, specify the Falcon Premium 12FT snap-on or 12FT lace-on. Pair with the Falcon Swivel Arm for a complete CAP 168-ready assembly, or browse the full aviation windsocks collection.
Need a written specification document for a tender? Contact the Falcon team and we will provide a CAP 168 compliance statement tailored to your site.