Rainfall rates are defined by MET definition or WXR return which depends on selections and settings.
How can ATC determine the rainfall rate without met/measured input? ATC reported moderate rain (a subjective assessment?) which agrees with the reported WXR picture. No active Cbs were reported in the immediate vicinity.
The crew described the noise as heavy (who would use ‘moderate’ without being able to distinguish between that and heavy, the assessment ‘heavy’ was also quoted after the evac, again subjective).
“As the aircraft approached Kingston there was light to moderate rain on the weather radar, there were no significant storm cells to fly around, and the radar was indicating a broad area of moderate rain”. P26
“When they intercepted the ILS runway 12, the weather radar painted light to moderate rain”. P27
“ … approach was noisy, because of the heavy rain”. P27 (subjective – noise)
“The first officer reported checking the weather radar returns in the Kingston area, noting that he saw a wide area of green with some yellow, indicating moderate rainfall, but saw no red to indicate convective cloud buildups with heavy rain. P54
The radar was painting light to moderate rain. P65
Runway braking action is based on the measured conditions or assessment according to the Braking Action Chart.
The reported water depth was 0.1in, but it was not established if this was actually measured nor if the next measured increment would be 0.2in.
0.1 equates to wet/good braking, the accident analysis showed medium/fair, yet 0.125 is flooded by definition; (note the possibility of a data gap #64).
How might the crew decide on the braking action based on the information available; according to procedure the WXR and audio cues should have prompted medium. The FO suggested a higher A/B setting which was set; but within this there may have been an underlying belief that the charted performance was sufficient. The crew apparently thought that a wet/good rating was sufficient (supposition from advanced analysis – wet/good may have provided a small safety margin, medium would not). The operator declined to explain ‘Advanced Analysis’; perhaps a gap between operators procedures and practice !!!
This is not to excuse the crew from their professional responsibilities, but an attempt to understand the issues which makes behaving as required very difficult.