Originally Posted by Norwegian
I am still struggeling here, but trying to understand.
An balanced field Lenght it a term that an airport designer is using? for designing a good RWY for operators.
An unbalanced T.O is used by pilots in determing best use of A/C perfomance to have a larger TOM using a redused V1 (above 1.05 Vmcg) to comply with ASDR , in cases where TODA is not equal to ASDA.
What then with the distance in speed difference between V1 and Vr, if you get an OEI here you willnot be able to fly, or stop.
No. You have to choose V1 to meet all the requirements, and/or reduce TOM.
Still requirements for an airplane regarding Takeoff requirement is to accelerate to V1 and then either stop or go and then reach screenheight of 35feet.
Balanced field takeoff is where you have no problems with either stopping or going and be within T.O req. regarding regulations.
Think of it like this.
Any given runway has an ASDA and a TODA. Because of the difference in rules for calculating ASDA and TODA, they need not be equal. If the airport either by design or accident ended up with TORA=ASDA one could say that the RUNWAY was 'balanced' in that case. That's the runway design side, and much less common usage.
Any given aircraft (including consideration of weight and all other relevant factors) has a TODR and a ASDR. Again, these need not be equal.
However, because both ASDR and TORA are dependent upon the choice of V1, and have opposite dependency on it, one can typically choose a single V1 where TODR=ASDR. In that case one can speak of the aircraft performance being 'balanced' and its typical to describe TODR=ASDA=BFL and quote that distance as the 'balanced field length'.
If ASDA=TORA, then the balanced performance is the best optimisation of V1 possible. If ASDA isn't equal to TORA, then logically the optimum performance is obtained when one makes use of as much of both the ASDA and TORA as possible. This is achieved by 'unbalancing' the calculation and selecting a different V1 to the 'balanced' case.
Note, however, that at all times you must have TODR consistent with TORA and ASDR consistent with ASDA; you will still be able to stop or go as required. You're just taking credit for clearway or stopway that the balanced calculations were forced to ignore.