Originally Posted by
Pugilistic Animus
You Can't use WET figures on DRY RWY
-----Why
You actually can. TOW for wet must never be higher than max allowable TOW dry. But before you do, please consider:
WET figures are calculated with the decceleration force of available reverses. On the other hand, DRY figures are based on brakes only. Hence on a DRY-figure takeoff, at V1 you start to brake and should stop by runway shoulder. If you use the reversers, your stopping distance will be
(much - not true) somewhat less than that (calculated). Using WET figures relies on both brakes and reversers so there are no more aces left up your sleeve.
WET figures assume minimum screen height of 15 ft. On the other hand, DRY figures require minimum of 35 ft. For balanced field, this translates to lower V1 figure to accomodate for longer braking distance on the wet tarmac.
Provided the runway is indeed DRY: should you use WET figures and elect to continue at V1, acceleration from a lower than required V1 will take longer and cover greater distance to lift-off, clearing DERA or CWY end by 15 ft. If you had used DRY V1, ENG failure (birdstrike) at the identical point of tkof roll would be still before V1 - so stopping is now a newly available option (with the extra comfort of using reversers not accredited within your ASD calculation); while an ENG failure at (the higher) dry V1 would give you 35 ft margin over the fence. The NW strut itself is 5 ft high on my aircraft.
FD (the un-real)
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