I spend a week each year at Boeing. I see the performance courses at both grades and know many graduates of them. Without exception skilled and dedicated people but they believe in the numbers and would offer up their first born such is their faith.
However, they are not at the pointy end.
I'm glad Dehavillanddriver offered up the example of Edwards and, as you're all using the internet, I'd like you to take a look at another runway - Moses Lake. It's significant because, as yet, Airbus don't have much penetration into the Oz market.
Use the free satelite imagery viewing sites to look at the runway - all 15,000 feet of it. That's where your performance figures were derived. Note the witness marks for the tests and the parallel nature of them as the TP's sidestep to get clear pavement - it is a competiitve business and they want the best figures possible.
Once you've viewed the images here's the sum up:
They are not performing RTO's on the caked contaminated crap we face but the figures are based on those conditions you see there. We do not have the luxury of sidestepping the touchdown zone on our real life runways.
For many intersection take offs it doesn't matter if you are tonnes underweight - the touchdown zone is where we are all applying maximum braking, the tyres (remember them?) are now very hot and we are digging them into the contamination while still a more than a thousand feet from the stop lights and the antiskid has ensured we're now carrying an even coating of crap with us.
Nobody is denying these takes off's have their place in operations but a wide eyed acceptance of performance data is very dangerous. The figures are as much the domain of the marketeers as the flight test department. There is no other reason for them to spend the last generation fighting all efforts to make them reflect the real lives of folks on the line.
Finally, for those of you into the extreme sport of competitive derating - have you ever researched - or your company passed on - the reductions in N1 or EPR that actually extend engine hot end life versus the thrust settings that are mere willy waving? Some interesting work on the subject that never reaches those on the line. Again, you're viewing this on the internet and you can google your way into knowledge if you care rather than just here to enjoy taking a poke at each other.
Here's the real performance calculation:
Intersection + willy waving derate + contaminated upwind touchdown zone + long taxi with multiple turns = baffled performance engineeer telling us it was the pilots' fault coz the figures said you could stop.
Regards to all,
Rob
Last edited by PPRuNe Towers; 15th Nov 2003 at 21:22.