J_T,
From an operational point of view, we dont have the time nor expertise to do AFM graph calculations prior to takeoff. We therefore use Balance Field Limits on Boeing aircraft with published weights and QRH speeds/FMC speeds, corrections for runway contamination, MEL/CDLs etc are then applied to these speeds.
On the A300 we use optimized v-speeds, while these can offer better weights, however its fun trying to explain why you get a 30 kt V1 increase for a 3,000 kgs weight increase.
Maxalt,
Balanced field length is the ideal situation where the maximum takeoff weight is possible for a given runway length.
This means that the aircraft can accelerate to Vef, suffer an engine failure and continue the takeoff reaching 35 feet by the end of the runway, or the aircraft can transition into a stopping configuration and stop by the end of the runway.
Unbalanced field length may also result from runway slope and wind corrections, and the use of clearways and stopways.
By definition a clearway doesn't have to support the weight of the aircraft, therefore if you are allowing the
accelerate go portion of your takeoff to be over the clearway, you are left with an unbalanced situation. I would therefore say that the statement which you were given is incorrect.
It Allows Maximum Performance Benefit To be Gained From any Clearway Associated With the
Runway
Mutt.
The statements in italics are taken directly from Boeing documentation, which i can send to you if required.