On airfields with a small volume of traffic, a ground information service can be sufficient. This will be supplied by an AFIS agent. In spite of fewer responsibilities, the functional needs of the AFIS are similar to those of airfield control.
Alternative to flight information
An AFIS service can be provided in the event that an airfield is not controlled. The AFIS organisation, set up on an airfield for the benefit of aircraft moving within the airfield circuit, must communicate the following to aircraft:
• The relevant elements for flight information and designated parameters; runway in use, direction and speed of surface wind and significant variations, ground visibility, quantity of low cloud and height of cloud base (if available), air temperature, altimeter setting (QNH), atmospheric pressure and exact time.
• Information available having a bearing on known traffic and especially traffic within the airfield circuit or in the process of effecting an instrument approach and other aeronautical activities which might concern pilots.
• Information available concerning the state of infrastructure, functioning of visual and radio aids, existence of construction or maintenance works, presence of obstacles on or near the platform, reference time, residues of falls such as snow, ice, frost etc.
The AFIS service must also:
• choose the runway or runways in use,
• place or cover ground signals,
• activate visual aids,
• monitor the state of the manoeuvre area,
• take appropriate measures when abnormalities are detected on the infrastructure or the airfield visual and radio aids,
• re-transmit to the air traffic organisation concerned any information or request emanating from an aircraft or an operator, especially requests for clearance from departing flights which will be controlled in the near future,
• operate the alerting system.
The person or persons responsible for the AFIS service therefore need a place which allows them to operate the service in good conditions. To a large extent, this area requires the features of a control tower used for airfield control. The person responsible for the AFIS must be able to see the whole of the airfield circuit and have easy access to the manoeuvre area.
Evaluation of size of airfield
On small or medium-sized airfields, airfield control is provided from a single control position. On the other hand, as soon as the quantity of flights increases in volume, it is no longer possible for a single agent to carry out the whole of airfield control. The result is several controls, or a system where each controller is only responsible for a part of the aircraft’s movement, except for the person in charge of the control tower (officer of the watch). The decision on the number of control positions necessary is the first step in the procedures for the design of a control tower.
It is also necessary to foresee the specific supplementary functions by which the work posts are affected such as the chief watch position, pre-flight position, signal command position, runway office etc. In addition, it is necessary to envisage the provision of control tower training for trainee controllers, where double positions are often required.