Mutt,
Agreed, on the one hand I was referring to basic Operations Manual BFL Charts where obstacles have to be considered separately.
On the other hand I was referring to those occasions when a published RTOW is invalidated (Usually by the appearance of a new obstacle), and in the interim period (often only a matter of hours) before the computer programme can generate temporary RTOWs, crews are required to use the "General Performance" data from the Operations manuals. This procedure is well spelled out to our crews, as I alluded to in a response to Mad (Flt) Scientist with the words "Whilst well written Operations Manuals are produced, and recurrent performance refresher courses etc. are carried out, there's still a significant number of pilots 'out there' who, having passed Performance 'A', promptly put it into the 'tick in the box' category and hope that they never need to use it. Every effort is made to convey to the pilot group the reasoning required to effect this, and it is gratifying that there is a growing awareness of performance appreciation and appropriate application in my company (This did not exist before, and I take some delight in having turned the tide).
The computer programmes that I've developed (from Manufacturer's AFM and Performance Manual data of course) rarely use the Balanced Field principal, as we regularly use Clearway and Stopway in MOST normal operations which, except in a few cases, are rarely equal. The major de-equalising (is that a word?) factor of course, is the presence of obstacles where the Optimised Continued Takeoff/Obstacle limit does not conflict with the separately computed Accelerate-Stop limit, the lesser of the 2 being the limit. This cannot be the case when forced to use "General Charts" when Balanced Field data is used in the instance of the RTOW being invalidated.
I mentioned elsewhere that I was primarily referring to the B777, but these same general principals, with their own idiosynchrasies, apply to the other aircraft that I do performance work for.
Sometimes I think we say the same things, but use different words.
Regards,
Old Smokey