I'm so glad you guys have posted this thread, you have inadvertently stumbled upon something I have known about for years, despite my best efforts nothing has changed. I will over simplify what I mean. So some performance software which was developed decades ago and properly certificated at the time has since been modified by programmers who may or may not know anything about aircraft performance, The training in its use becomes less thorough, simply because the person teaching you how to use it doesn't really understand it themselves. Then one day runway performance data is presented to a captain who knows his **** and knows exactly how his aircraft will perform both on one and two engines. he asks himself the question how is it this runway has no takeoff weight limit and no special procedure when I can see the obstacles and terrain sitting right there in front of me, off the end of this very runway. Be aware people, not everything is what is seems, despite the fact that the data was generated by an approved person using authorised software. This issue is in every australian airline today.. Beware.