There's a recommendation until a redesigned rudder power control unit, installation of a new yaw damper system and a rudder pressure reducer. For flap setting of Up, 1, 5 and 10, pilots must increase block speeds by at least 10kt. Block speeds are the maneuvering speeds recommended by Boeing. They are approach speeds for a specific flap setting for a correponding range of weights. In case of a full roll control from the ailerons and spoilers to counteract any inadvertent rudder input speed must be above "crossover" speed. Below that speed roll induced by the rudder can exceed the lateral control authority.
After some analysis a new block speeds were recommended:
Weight up to 53,070kgs - Flaps up 220kt, Flaps 1 200kt, Flaps 5 190kt and Flaps 10 170kt.
Above 53,070kgs up to 62,823kgs - Flaps up 230kt, Flaps 1 210kt, Flaps 5 200kt and Flaps 10 180kt.
Above 62,823kgs - Flaps up 240kt, Flaps 1 220kt, Flaps 5 210kt and Flaps 10 190kt.
Note: Increasing block speeds during takeoff is not required. Airspeeds required by non-normal procedures must be followed instead of the revised block speeds. B737NG's are not affected by this new block speeds because they are equipped with a rudder limiter system.