Calvert Cross Bar Approach Lighting System
The photo above shows the Calvert High Intensity Approach Lights on Essendon's Runway 26 shortly after they were commissioned. Being a time exposure, the lights of aircraft landing are shown as long streaks terminating at the runway threshold. This photo also gives a good impression of the positioning of the lights among the houses of the suburb of Strathmore. The photo was taken from Gaffney Street looking across the Moonee Ponds Creek valley.
The following information about the Calvert cross bar lighting system is based on an article High Intensity Approach Lighting by S.W. Hart (DCA Sectional Airways Engineer) which appeared in the Civil Aviation Jounal, the DCA's house publication, Vol 1, No 3, March 1951.
In 1946 Mr E.S. Calvert of the Royal Aircraft Establishment, Farnborough, UK, was requested by a UK Ministry of Civil Aviation Airfield Lighting Committee to investigate the problem of approach lighting and establish the general principles involved. Calvert tackled the problem by attempting to ascertain the visual and mental processes by which a pilot lands an aircraft. He then developed a theoretical model by which different lighting systems could be compared, and tested his theoretical results using simulation.
Calvert's line of reasoning led him to the conclusion that to provide smooth transition from instrument to visual flying without optical illusions, and to provide sensitive and natural indications which could easily be interpreted by the average pilot, the approach lighting pattern should consist of a centre line of light with horizontal bars of light running transversely across it at even intervals. This pattern consists of two basic elements - a line of lights leading to the runway threshold, and horizontal lights to define the attitude of the aircraft. Calvert placed much stress on roll guidance compared with the Americans who, up to that time, had completely neglected it. He was the first to realise that it was easy to confuse lateral displacement with angle of bank.
The Calvert system does not indicate a defined glide path, but the widths of the horizon bars are such that, if a pilot maintains a glide that will take him to the correct touch down point, each bar will appear to be the same width as the previous one as it disappears under the nose of the aircraft. Distance is indicated by using single lights in the centre line to indicate 1000 ft or less from the threshold, double lights for 1000-2000 ft and triple lights for 2000-3000 ft.
It is interesting to note that the basic form of the Calvert cross bar lighting system still forms the basis for high-intensity approach lighting systems today.
Below: A modified form of the basic High Intensity Approach Lighting system is used on some capital city precision approach (ILS) runways, in this case on Melbourne/Tullamarine's Runway 27. The main difference is the larger array of lights just prior to the threshold.