Norwegian,
If I may add a comment and paraphrase MFS and Bigmosquito ..
An balanced field Lenght it a term that an airport designer is using? for designing a good RWY for operators.
The term "BFL" can be used by the
(a) runway designer (and OverRun certainly has a lot of runs on the board in that discipline ..) talking about lengths at a particular airport, or by the
(b) ops engineer (performance engineer .. whatever term you prefer) and flight crew looking at how we can get the aircraft out of a particular runway on a particular day.
For your purposes, I think that you are concerned with (b) ?
There are two main goals, either of which is valid and reasonable in different circumstances ..
(a) simplicity of calculation (BFL is always going to give you the simplest calculation .. now wait for someone to cite an example where that might not apply ..) or standardisation (for example to make it easier to use FMC/FMS calculations) .. generally we will go with a BFL approach every time
(b) achieving maximum RTOW (RTOM, whatever term etc..) or some similar criterion. Generally, this will NOT be achieved for BFL and we usually have to do a few more calculations (associated with not using BFL) to get to the desired goal.
Now, if we are doing the non-BFL calculation, there will be a whole lot of calculations to do to ensure that ALL the various requirements are met .. the requirement which gives the LOWEST TOW then becomes limiting and defines the permissible maximum TOW for the conditions.
These can be presented in different ways according to the preference of the engineers (generally from the aerodynamics group at the OEM) and whatever standard approach a particular OEM might have. Some OEM, for some aircraft, don't even give you a choice .. they only present the AFM data for BFL conditions.
The OEM will set out to keep his AFM reasonably thin and not have it extend to numerous volumes so there are various tricks to the trade in developing the different typical styles of presentation .. and the previous post highlights some of these.
Main thing to keep in mind is that, doing it by hand (which would apply to any calculation done in the field by the pilot without a fancy computer in his nav bag), the BFL calculation (simplified for obstacle assessment) might take 10 minutes or so while the non-BFL optimisation for a runway with a few obstacles can take an hour or two to finish ... I used to figure on a half day to a full day for a typical manually derived runway RTOW chart.
Thank heavens we now have computers .. either one uses the OEM provided program or develops one oneself to emulate manual techniques and the PC can figure the answer in a matter of seconds/minutes according to the complexity and how far one wants to push the calculation "accuracy" ...
Balanced field takeoff is where you have no problems with either stopping or going and be within T.O req. regarding regulations.
Not quite.
You can have plenty of problems stopping or going whether the takeoff is BFL or not BFL. With the unbalanced T/O, either ASDR and/or TODR/TORR (generally for one of the TOD or TOR cases) will be limiting .. The only time that there is a reduced anxiety load for the pilot is when the required distances are very much less than the available distances and there are no obstacles of any significance for the calculation .. otherwise, every takeoff should still involve a bit of mental sweatiness for the pilot .. both seats, not just the PIC.