Where an EU operator is approved to operate in contaminated conditions suitable (approved) data must be provided. One means of compliance is given in CS-25, AMC 25.1591. This requires an explanation of the basis of the data, its limits, and the assumptions in use, to be included in the AFM.
The range of contaminants, including depths to be considered, are given in para 5.
The CS 25 information should apply to an older JAA approval as the new CS-25 AMC is based on draft JAA proposals (NPA) for calculating contaminated data.
Note the general assumptions in CS-25 AMC 25.1591 and caveats about data calculation; whether reverse thrust use is assumed or not, the relative risks compared with normal operations, and procedures to be used.
para 8.1.1
Operation on runways contaminated with water, slush, snow, ice or other contaminants implies uncertainties with regard to runway friction and contaminant drag and therefore to the achievable performance and control of the aeroplane during take-off, since the actual conditions may not completely match the assumptions on which the performance information is based. Where possible, every effort should be made to ensure that the runway surface is cleared of any significant contamination.