Originally Posted by
Gary Lager
There are quite a few mistakes in that book. Have a search for previous threads here on PPRuNe. If what you read contradicts what you previously understood, don't panic straight away!
However, it's my understanding that the reduced screen height is in some part due to the possibility that the aircraft may be committed to takeoff with an engine failure shortly after Wet V1, but still a few knots below the usual dry V1.
Remember that unless you are field length limited, then there will be a range of speeds from which a safe takeoff or a safe stop are both possible.
Much depends on how your company has elected to conduct its performance calculations (balanced vs unbalanced field etc) - best to ask them for the definitive answer.
My company uses optimised runway-specific data, with separate tables for WET conditions, so our 'V1' can account for both a safe RTO or a safe takeoff in the event of an Eng failure, albeit with a reduced screen ht.
But just why is a takeoff from wet runway to 15 feet screen (which is allowed) more safe than takeoff from a dry runway to 15 feet screen (which is forbidden)?