During the recent snow/sleet we were operating from a runway with a 35 metre cleared width, within which there was 15-20% of slush to a depth of 4mm. My understanding is that a contaminated runway is one where there is more than 3mm water or equivalent... in this case that would be 2mm of slush. Am I doing OK so far?
As we couldn't use wet performance, the only relevant data we had was for 6.3mm (1/4inch)slush and using these figures lead to a reduction of 11 tonnes RTOM. Another company, operating same type of aircraft (A321)said that their ops manual allowed the runway to have up to 25% contaminant before they had to apply these decrements, and I don't question their veracity for one moment.
Neither of us could recall seeing anything like this in our company manuals or in Jarops manual (and we trawled through them down route). Have we missed something blindingly obvious, in which case please help, or is it simply a case of different companies using different criteria as is often the case with performance.
Oh by the way, we departed after I had carried out a visual inspection of the runway. The crews had done an excellent job. What are your views?