I find the old rubbish of runway behind you, fuel in the bowser, sky beneath you rubbish from yesteryear, just that, rubbish from yesteryear. The modern world still requires airmanship and at times, because of the way modern systems work, maybe more than it did in years gone by. I'll return to that later.
Our Mad (Flt) Scientist has brought an important issue up. Slope affects the position relative of objects when airborne, especially those close in and knowing that these things have been taken into account by the Performance guys would be comforting. It is especially important if you depart from an intersection on a runway that starts with a downslope. Our company have assurances from those who supply our performance data that 1) Declared distances used are matched in the tables and 2) The (revised) slope is taken into account. We have been supplied with (generic) diagrams that show us the point on the runway where the declared distances are measured from. We also have data that gives a (very) conservative distance vs. weight penalty.
Returning to the rubbish. When you work for a reasonable company, you are not asked to fly outside the rules. You are not pressured to fly without sufficient fuel. You are not made to 'flex' every flight. And as a commander, together with your crew, you try to operate safely. That means sticking to the rules, following the performance charts and operating in accordance with SOP's. When these things let you down or you can see problems ahead, that's where the "Airmanship" kicks in. Take for example, intersection takeoffs. Is it always more dangerous to do them? Without more data, how can you know? I can tell you that the speeds will often be different and as such, the possibility of a 'reject' will vary, as will the chance of a tyre failure etc. And we haven't considered the tyre and brake heating up as Captain "Ultra Safe" taxies the extra kilometer to avoid the intersection take-off. And this "fuel in the bowser" rubbish. Knock yourself out if you wish and fill your plane up every flight - after all it's safer, isn't it? Obviously the extra weight won't increase the take-off speeds, reduce the climb rate, increase the landing speeds and distances required, or will it? So you'll just add a ton then? Is that just 5% safer or a full 10% safer?
Then we have de-rating/flexing etc. Safer or not? What is for sure is that you'll run cooler engines, reduce the chance of a failure, reduce VMCA and you'll still have Full Whack available if you need it. You'll also have an artificial weight penalty "to add a bit for mum and the kids."
Like most things, we have to make compromises. We make these compromises based on knowledge. Our job is therefore to trade economy for time and convenience - not safety. And safety is a shared responsibility for the regulator (eg. In Europe he knows we do flex. and intersection departures, he approved the figures and calculation methods), our companies, the manufactures and last of all, US!
Safe flying,
PM
PS: Good question Mad (Flt) Scientist