PM, ‘me thinks you assume too much.’
“… while approaching UK airport…” How can we visually differentiate between a dry tarmac runway and a damp ‘grey’ concrete runway, or even a tarmac runway with a slight change in colour = damp?
Jw, re engine failure, which might be better; a reduced screen height with a ‘go’ on a dry runway using wet performance, or a stop on a misjudged wet runway using dry performance.
Cosmo, ‘what legally matters’ is the judgement of the investigation after an event; there is no ‘legality’ beforehand, as the process depends on an adverse outcome.
Using WET cautiously should not be considered as ‘foot shooting’ or ‘covering backsides, but that it could be the better judgement for a safe operation based on the information available.
ICAO circular 329
“damp runways effectively reduce aircraft braking action below that of a clean and dry runway.”
Draft ICAO Industry best practices manual for timely and accurate reporting of runway surface conditions by ats/ais to flight crew.
“Because the aviation community is heading towards a three-point scale for runway state (i.e., dry, wet, or contaminated), the need for a definition of damp can be questioned, as a damp runway would be considered to be wet. However, there are a number of performance standards and advisory circulars presently in force that would require a definition for damp. Consequently, a definition for damp is still believed to be required until consistency is achieved with respect to the associated performance standards.”
For performance standards; Damp=Wet.