The actual site for the aerodrome, and the alignment of the runway(s), would depend on the land available and the direction of the prevailing wind. For aircraft of 5700 kg MCTOW or less, the maximum crosswind component, ie the component of wind acting at right angles to the centre-line of the runway, should not exceed 9 knots. It is therefore important that the runway is constructed so as to face into the prevailing wind as close as possible. This wind direction may be based on experience, but ideally should be determined following observations taken over as long a period as possible.
Clear take-off and approach airspace 'surfaces' are also required. For daylight operations only, these surfaces continue out from each end of the strip for a minimum distance of 1.2 km. For aerodromes intended for night operations, the distance increases to 3 km. Ideally, these surfaces should not climb up over residential areas or tree plantations.
These approach and take-off surfaces should remain clear of obstructions for the life of the aerodrome so it is preferable that, even if the aerodrome operator does not own the land below the approach and take-off surfaces, some control is obtained through landowner agreements or local town planning. Further details of these surfaces are given in the next chapter.