Originally Posted by Underfire
That extra 12 feet puts you quite a ways down the runway.....
Isn't it actually 22' compared to the 50'AGL crossing height assumed for the landing performance? I make that approx 22x 20* = 480' or about 135m reduction in runway available. That takes the effective landing distance down to slightly under 1700m, assuming that you are exactly on the visual slope. Not a lot of runway in the wet on that machine.
A recent report on a over-run near miss in Christchurch shows what effect just a little bit of ponding can do to the braking action:
Reduced braking effectiveness during landing involving Boeing 737-800, VH-VOP at Christchurch Airport, New Zealand on 11 May 2015
*3 degrees is 5% = 20 x factor