The Signal Square & Other Visual Signals to Aircraft
by Roger Meyer
The Signal Square was neither fish nor fowl. It was installed and maintained at aerodromes by Airports staff, and operated by the resident groundsman or airport fireman on the instruction of the air traffic controller or flight service officer.
The Signal Square, or signal area, contained symbols to indicate visually to over-flying aircraft conditions on the aerodrome. It had pre-War origins, supplementing an earlier set of ground signals, and was intended for aircraft that carried no radio communications equipment (which included most light aircraft well into the 1960s). As soon as ICAO was created in 1947, Annexe 14 contained (and still does) instructions on the size and construction of the Signal Square. Annex 2 describes its use by aircraft. Ground signals are still used at aerodromes to this day the landing T and the gliding-in-operation symbol being the most common ones, but the general use of the signal square had fallen into disuse by the late 1950s when VHF air-ground communications had been largely introduced.
square was marked out on the ground in the vicinity of the control tower and the
wind- sock. It had sides 40 feet long, with a white-painted border. The surface
inside the square was smooth and level, surfaced in bitumen, ashes, sealed gravel,
turf or even bare earth. It was usually blackened with sump oil or black ashes
to provide a contrasting background to the symbols that conveyed the information.
The were four basic signals; the red square signal, the dumb bell signals, the
landing T, and the right hand circuit indicator. All of these objects were made
of timber and painted black on the reverse side. They were made of a series of
hinged sections so that they could be folded up when not in use, and would not
be visible from the air as the reverse side was showing, and appeared black.
Left: This aerial photo of the hangar area at Melbourne/Essendon c.1947 shows the signal square at the bottom right of the image, with the wind T signal clearly visible.
The dumbell signal indicating that the unsurfaced areas of the aerodrome are unserviceable is also displayed, as is the red square with yellow diagonal indicating a bad state of the aerodrome surface requiring caution.
Roll your cursor over the image to identify some other features shown in the photo.
(Photo: CAHS collection)
Hand Circuit Arrow:
Left: The Signal Square at Hobart/Cambridge in 1942, showing the unsurfaced movement areas are unserviceable and that pilots should use caution when landing.
Click here to see the full photo.
(Photo: CAHS/Rod Torrington collection)
While not directly related to the signal square, it is worth recording here several other aerodrome conditions that could be conveyed to aircraft via symbols mounted on the control tower. These were the Airport Altitude Sign in 8" high letters, and above it was the duty Runway or landing Strip Number Sign (e.g., runway 09).
Cane balls could also be raised and lowered on a gantry above the tower cabin. A raised yellow ball indicated that the Aerodrome Control Officer was not in attendance. The black ball was called the no wind signal, and indicated that the take-off direction was to be verified with the Aerodrome Control Officer. These symbols had generally fallen into disuse soon after the war.
Click here to see a photo of a Controller using the Aldis signalling lamp & Very flare pistol
The writer has observed differing interpretations of the meaning of some of these symbols, and invites comments from older readers who had first-hand experience with any of these aerodrome tower or signal square symbols.
the more modern Signal Area