ICAO 9837 AMD 2 PDF

INTRODUCTION

Wind has a direct impact on aircraft. The direction of the prevailing wind is taken into account when planning a new runway. Headwind components determine the direction of take-off and landing and crosswinds force the pilot to compensate for the drift.

An important characteristic of wind is its temporal and spatial variability. Pilots need to be aware of local wind conditions at the airport, especially during approach and departure. Temporal variability makes it necessary to define multiple parameters related to wind: mean, minimum and maximum values. Spatial variability is mostly related to temporal variability and can, for example, lead to a relative movement of gusts (like ripples on a body of water). It can also be related to terrain effects of the aerodrome or its surroundings, or to the presence of obstacles. For these reasons, Annex 3 — Meteorological Service for International Air Navigation recommends that wind observations for local reports be representative of the touchdown zone (for arriving aircraft) and of conditions along the runway (for departing aircraft), which sometimes leads to the installation of multiple sensors.