Do any manufacturers quote damp performance? How has this been justified?
Here is a recent AIRBUS answer to the request of my company
The European Operational regulation still states in CAT.POL.A.105 that “For performance purposes, a damp runway, other than a grass runway, may be considered to be dry.” However, the FAA Takeoff and Landing Performance Assessment Aviation Rulemaking Committee (TALPA ARC) considered that a damp runway should be considered as wet for performance assessment, both at takeoff and landing.
Airbus has changed its policy in line with the TALPA recommendation and considers that when a runway is reported as damp, performance should be calculated for wet/good braking action. You will note that in the FCOM PER-TOF-CTA 20 there no longer is a statement on the equivalence of damp with dry, instead all water-contaminated runways with a depth of less than 3mm are considered to be equivalent to wet. Furthermore, in FCOM PER-LDG-DIS-MAT, you can see that the damp runway condition is clearly associated with wet/good in the Runway Condition Assessment Matrix.
The reason for this is flight test and operational experience showing a notable braking performance reduction on runways reported to be damp. While in many cases braking action remains better than the regulatory friction curves for wet runway, there is also an issue of timely reporting by the airport of a change from damp to wet during rain showers, which makes the new policy of considering damp as wet a reasonably conservative approach.