Performance on a damp runway vs wet/dry
When working out take off performance on a damp runway do you use dry or wet runway performance figures?
The FAA does not make any reference to damp runways, whereas JAR-OPS 1.475 states that a damp runway can be considered dry in terms of takeoff performance.
But how accurate is this?
On one hand using wet performance reduces margins by reducing screen height to 15ft and including the use of reversers in the calculation.
On the other hand using dry performance assumes a braking action/friction coefficient that you are unlikely to fully achieve particularly as you approach the rubber coated touchdown zone of the reciprocal runway.
What do you personally use and why? And what guidance, if any, does your company provide?