Elements for Life

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] 103

ETEOROLOGICAL INFORMATION PLAYS

an essential

role in air navigation and is required to ensure the

safety and efficiency of civil aviation operations. Most

people working in the aviation industry or meteorology are

familiar with the effects of hazardous weather phenomena on

flights. Pilots, dispatchers and air traffic controllers need obser-

vations, reports and forecasts as well as warnings of such

phenomena. What is often less clear is the important effect that

seemingly ‘innocent’ meteorological elements (such as surface

and upper winds, visibility and runway visual range, temper-

atures and surface pressure) can have on the safety and

efficiency of flight operations.

Information on wind direction and speed is vital for take-off

and landing, and is the basis for the choice of runway. If the head

or tailwind component and the crosswind components are made

available separately, the length of runway needed can be deter-

mined. One can also ascertain whether the crosswind

component falls within the design limits of individual aircraft.

For the en route phase of flight, information is required on winds

along the route at cruising levels. Strong headwinds mean that

more fuel must be carried at the expense of passengers or freight.

Pilots need to know what the temperature will be at their

flight level because temperature affects jet engine efficiency.

The same applies during take-off: a higher temperature results

in a longer take-off run because temperature affects air density.

Temperature affects the lift at a given speed and hence also the

take-off run. Similarly, atmospheric pressure affects the take-

off run due to its relationship with air density.

The surface wind, temperature and pressure referred to above

have to be accounted for in pre-flight calculations for the take-

off run. The provision of accurate and timely information on

these meteorological elements helps ensure the safety of flight

and also improves the efficiency of airline operations.

Information on visibility and runway visual range is of crit-

ical importance as landing and take-off minima are

determined on the basis of these elements, and precision

approach operations cannot take place without them.

Furthermore, the height of the cloud base is highly useful

WMO and ICAO: working together

for international air navigation

OM Turpeinen, International Civil Aviation Organization Secretariat

A higher temperature results in a longer take-off run because temperature affects air density