How wet is wet....
Have been reading with interest entrys regarding tarmac friction measurement and aircraft braking perormance.
In a previous life I worked for many years on race tyre development, and reading from the pages of PPRuNe it appears the CAA have fallen into the trap (like some race tyre developers) of not recognising "degrees of wetness". A runway is regarded only as either "dry" or "wet".
For a race car the difference in lap times (ie tyre performance) between a damp circuit and a circuit with standing water, could be around 50%. But by definition both are "wet".
We found "degrees of wetness" very difficult to define for the purposes of tyre testing and invariably we resorted to a finger in the air type guestimation. Add to this that wetness of tarmac is inconsistent - at a given moment it either drying or getting wetter.
Given that aircraft tyres (by neccessity due to abuse) are not heavily treaded for water clearance and the fact that they are lightly loaded for a high proportion of the time they are used in anger (especially on the roller coaster ride like BRS 09/27 !) reduction of performance in "very wet" as apposed to "moderately wet" conditions is a factor the CAA bofins might want to consider.