...all very strange as the braking action was good before they started brushing and it has only rained since they started.
If the rain initially fell onto a sub-zero temperature runway surface, it would create a thin layer of ice which would cause poor braking action.
Since a runway's white runway markings retain less heat than its other surfaces, it's usually these that can be slippery with ice before other surfaces follow suit.
Freezing rain or rain falling onto freezing surfaces is the most likely cause of the poor braking action which can be addressed by the application of chemical de-icing agent.
Brushing on the other hand, is a total waste of time!!
Any LLAO Ops vehicle driver's visual inspection is likely to be only partially effective - a full braking action measurement is the only way to accurately assess the situation. This requires a runway closure for around 10 to 15 minutes.
