The term Reduced Aerodrome Visibility Conditions (RAVC) has been established to define those meteorological conditions where all or part of the manoeuvring area cannot be visually monitored from the control tower and consequently the personnel of the control units are unable to exercise visual control over the traffic in the area.
To describe the ability of the personnel of the control units to exercise visual control over all traffic and of the pilots to avoid other traffic, four different visibility conditions are defined from Visibility Condition 1 through to Visibility Condition 4. The following graphic shows the relationship between the various Visibility Conditions.
Reduced Aerodrome Visibility Conditions (RAVC)
- For taxiing, this value is normally taken as visibilities equivalent to an RVR of less than 400m but more than 75m. The value of 400m is provided as an example in Doc 7030. Criteria for determining the transition between visibility conditions are a function of local aerodrome and traffic characteristics.
- This value is normally taken as an RVR of 75m or less.
The transition from Visibility Condition 1 to Visibility Condition 2 occurs when meteorological conditions deteriorate to the point that personnel of control units are unable to exercise control over traffic on the basis of visual surveillance and in practice defines the entry to Reduced Aerodrome Visibility Conditions (RAVC). The transition will be different for each aerodrome, depending on factors such as the location and height of the ATC tower and the size and layout of the manoeuvring area. Reduced ground visibility will normally be the determining factor for this transition. However at some locations, such as those with tall control towers, low cloud may be a prevalent factor requiring consideration. The process of determining the boundary between Visibility Condition 1 and Visibility Condition 2, and hence the entry to RAVC, will be an aerodrome-specific exercise.
The transition from Visibility Condition 2 to Visibility Condition 3 will be determined locally depending on factors such as the layout and complexity of the taxiway system, the types of aircraft operating. For taxiing this is normally taken as visibilities equivalent to an RVR of less than 400m (Doc 9476).
A study was conducted by Eurocontrol to assess the transition from visibility condition 2 to visibility condition 3. The main conclusion of the study is that the visibility threshold below which pilots are unable to comply with ATC instructions based on traffic information requiring him to see and avoid traffic is somewhere between 200m and 300m. Traffic information becomes less effective from visibility 300m and below, reaching its efficiency limit at visibility 100m (Eurocontrol A-SMGCS VIS2 – VIS3 Transition Simulation Report).