2015-08-21
567
Additional visual aids to navigation consist of markings on the aerodromes. These markings comprise single lines or rows of lines which, for the pilot, are very important for holding positions, runway thresholds, the runway centre lines, the sides of the runways, etc. etc…
However, at night or during poor visibility by day, lights are required. For lights to be effective they must be of adequate intensity. (1) At certain aerodromes the controller can vary the intensity of some of the lights so that they can be reduced to avoid momentarily blinding the pilot and strong enough so that he can see them in thick weather.
The first light a pilot sees on approach is generally the aerodrome beacon. (2) It may rotate (3) and can be seen at a great distance distinguishable by its coloured flashes (4) alternating with white, or white only. There might be an identification beacon (5) which shows green flashes of light which identify the aerodrome in morse code. (6) Red lights, the usual danger signal, warn pilots of the obstacles such as hangers and other high buildings, telephone poles, etc. Runway edge lights (7) identify the runway and approach lights assist the pilot to align (8) himself with the runway.
Lights may also be used to provide a glide path similar to what an ILS provides electronically. The Visual Approach Slope Indicator System, better known as VASIS (9), is a beam of light having a white colour in its upper part and a red colour in its lower part. A pilot of an aeroplane during an approach will:
a) when above the approach slope, see the lights to be white in colour;
b) when on the approach slope, see the lights to be pink in colour; and
c) when below the approach slope, see the lights to be red in colour.
By reference to VASIS, combined with ILS, the pilot can bring an aircraft down safely almost to touchdown by day or night.
After landing, he follows the blue taxi lights along the taxiway to the apron and the service areas.
At the service area a marshaller (10) with illuminated wands (11,12), directs the aircraft with signals to its proper position for unloading and, finally, signals pilot to cut his engines. (13)
