Complete the following sentences using the words from the box.

Weather and Air Traffic Control

A ccurate weather forecasts are essential to aviation. A pilot before taking off obtains a weather forecast giving him the weather conditions which are expected along the route of the flight and at the destination. As weather conditions affect aircraft in flight, meteorologists provide pilots and air traffic controllers with special aviation forecasts.

The basic weather report follows a standard format. First comes the wind speed and direction, usually in knots or meters per second, then the visibility in meters when less than 5 000m and in kilometers when 5000m or greater.

T he next item is the weather, for example, rain, fog, mist, haze, snow, etc. Cloud base is measured by means of a cloud base recorder which scans the sky overhead with a laser. Pilots’ reports can be requested to confirm the base. Cloud amount is measured in oktas but it is passed to a pilot like this: sky clear, 1-2 oktas as few, 3-4 oktas as scattered, 5-7 oktas as broken, and 8 oktas as overcast.

A major weather problem is thunderstorm, which presents a variety of hazards to aircraft. Aircraft will avoid thunderstorms that can cause delays as routes are closed due to thunderstorms. This information is passed as a forth group.

Air temperature is given in degrees Celsius. The dew point is also important because if the two figures are close together fog may soon form. As for QFE and QNH, they are passed in hectopascals.

Where the weather conditions meet particular criteria – visibility of 10 km or more, no precipitation, no thunderstorm or shallow fog, no cloud below a level of 1 500 m and no CB at any level – the word “CAVOK” is passed.

I n foggy conditions Runway Visual Range, or RVR is passed. It means how far the pilot is likely to be able to see along the RW. Measurement only begins when the meteorological report gives a general visibility of 1 500 m or less, and the pilot decides whether or not it is within the limits known as “company minima”(a pilot’s minima of a certain airline company) for landing or take-off. RVR is measured at touchdown, mid-point and stop end by the human observer method or by means of electronic equipment.

W indshear presents a serious danger as it is invisible and it might cause the aircraft to stall or undershoot the RW. The information about wind shear is included in the ATIS broadcast.

Another major hazard to aircraft is easier to measure. This is poor braking action. When the RW is icy, or if there is snow or slush on the RW.

P ilots usually report any unexpected weather phenomena which they encounter, severe turbulence or icing, any condition they think may affect the safety of flight.

A t many busy airports the current weather is transmitted on the terminal VOR frequency. This service is known as ATIS. As well as the weather report it may include useful information such as a type of approach, any holding delays, etc. Each ATIS broadcast has an identifying letter which a pilot must report to an air traffic controller on first contact.