Balance the go and stop cases
Move V1 and see why stopway and clearway pull the solution in opposite directions.
What does balanced field length actually balance?
At fixed mass and conditions, increasing V1 usually increases accelerate-stop distance and decreases the engine-out accelerate-go distance. Their intersection is the balanced field length and corresponding balanced V1 when the governing definitions and available distances permit that construction. The all-engine distance and independent speed limits can still govern.
Find the intersection
At fixed mass and conditions, increasing V1 usually increases accelerate-stop distance and decreases the engine-out accelerate-go distance. Their intersection is the balanced field length and corresponding balanced V1 when the governing definitions and available distances permit that construction. The all-engine distance and independent speed limits can still govern.
A runway is not automatically balanced because TORA equals TODA equals ASDA. Balance describes the selected performance case. Where declared go and stop distances differ, or independent constraints bind, the optimum can be unbalanced. A feasible V1 range lies between the lowest speed satisfying go and the highest speed satisfying stop, intersected with control, rotation and energy limits.
Extensions change the optimum
Additional stopway can permit a higher V1, shifting more demand to stopping and reducing the engine-out continuation requirement; this may allow more mass. Additional clearway can permit a lower V1, shifting more demand to the airborne go distance and reducing stopping demand. These are normal trends, not guaranteed results when another limit binds.
Field-length-limited take-off mass is the highest mass that simultaneously fits the required run, go and stop cases with a permitted speed schedule. Wind, density altitude, slope, surface, thrust and flap change it. Selecting a V1 toward one end of an allowed range involves the approved procedure and its priorities, not personal preference to ignore a constraint. If the feasible interval closes, reduce mass or change a valid input and recalculate.
Can you make the performance decision?
Four original questions. Work from the stated conditions and review the reasoning.