Guidance for Aerodrome Operators
It is the responsibility of the aerodrome operator to ensure that when the aerodrome is available for use the movement area remains safe for the operation of aircraft at all times. Additionally, CAP 168, Licensing of Aerodromes, Chapter 10, Aeronautical Information, requires ‘that all information relating to the aerodrome and its facilities, which is significant for the conduct of flights to and from the aerodrome, is available to users of the aerodrome.’
Major UK licensed aerodromes make every effort, within the limits of manpower and equipment available, to keep runways clear of snow, slush and its associated water, but circumstances arise when complete clearance cannot be sustained. In such circumstances, continued operation involves a significant element of risk and the wisest course of action is to delay the departure until conditions improve or, if airborne, divert to another aerodrome.
Feedback from operators has shown that information on the type, depth and extent of contamination of the runway (and/or taxiways and aprons) is often incomplete or out of date. Consequently, and especially during adverse weather, any significant change in the runway state should be made available to crews through the following means:
The depth of contamination is reported in millimetres for each third of the runway length. Reports will be given sequentially for each third of the runway to be used, for example, 'Runway surface is wet, water patches, wet'.
Where an aircraft will not make use of the entire runway, the third most likely to be used at high speed is the most critical. Depths greater than 3 mm of water, slush or wet snow, or 10 mm of dry snow, are likely to have a significant effect on the performance of aeroplanes.
A subjective assessment is also made of the nature of the surface condition, on the following scale:
(a) Dry Snow
(b) Wet Snow
(c) Compacted Snow
(e) Standing Water. None of these can be measured in situ
Note: Standing water is considered to exist when water on the runway surface is deeper than 3 mm. Patches of standing water covering more than 25% of the assessed area will be reported as water patches and should be considered as contaminated and will be reported as flooded when more than 50% of the assessed area is covered by water more than 3 mm deep.
It is difficult to measure, or to predict, the actual level of grip or value of displacement and impingement drag associated with a contaminated runway. Therefore, it follows that aeroplane performance relative to a particular contaminated runway cannot be calculated with a high degree of accuracy. Aircraft type design organisations (manufacturers) normally publish de-icing procedures in the relevant aircraft Maintenance Manuals. Any 'contaminated runway' data contained in the Flight Manual should be regarded as the best data available.