Table 1, Annex 1, of AC91-19 is not particularly useful; the industry’s current focus is on crew assessment based on the reported type of contamination and depth, as with the Airbus matrix. The matrix originated from TALPA which FAA has trialled, but is struggling with regulatory approval.
The braking action based on the AC table is of little value unless you know what ‘normal’ or ‘reduced’ deceleration means for your aircraft, - and in the same conditions as expected, and with a particular level of braking and/or reverse; i.e. was the deceleration from the brakes (relevant to BA/runway condition) or reverse (meaningless).
If the BA report is from a PIREP (TALPA only allows a down grade) then without knowledge of the reporter’s aircraft type, braking/reverser level, etc, the report is of limited value, unless you wish to bet your butt on the feeling in someone else’s (deceleration) – nor will the fact that they didn’t go off the end will not guarantee you stopping safely.
The measured accuracy of MU varies considerably with machine and contamination type; IIRC European ATC do not report MU, only contamination type, depth, extent, …
With heavy rain, WXR may help. A reasonably well-drained runway having experienced an area of ‘red’ WXR may take up to 15 mins to drain below a flooded category (NASA ref somewhere). This is subject to surface type, crowning/slope and crosswind. There can also be problems with ‘bitumen dams’ between concrete blocks or 'dishing' of old blocks where the center is lower than the edge.
Crews are expected to assess potentially inaccurate information and judge a safe course of action based on the expected landing distance. The recommendation is to add a minimum of 15% to the ‘actual distance’ for variable performance, but perhaps a bit more is well justified by the unknowns.
Edit - NASA tech memo 72650 ‘Wet runways’ W. B. Horn (
http://ntrs.nasa.gov/archive/nasa/ca...1975012279.pdf)
Runway drainage: “In general, runway water depths increase with increasing rainfall intensity and drainage path lengths, and decrease with increasing runway transverse slope and surface macro-texture.”
“surface winds tend to increase drainage path lengths and can greatly increase water depths on the runway, depending upon the wind magnitude and direction.”
Braking is affected by surface micro texture and tires:
“… tire tread designs can improve tire/pavement drainage and reduce braking traction losses to some extent, but are not as effective in this regard as improving the pavement surface micro/macro texture by pavement grooving. Research indicates that tread designs tend to lose their drainage capability when the tread is approximately 80% worn.”
Know your tire condition; beware smooth concrete runways.