Originally Posted by
cardiomd
So if you have estimated 50' clearance 6000 ft after running the numbers, planned on 28L which is 8500', and switch to 28R which is 7500, would you re-punch into the FMS or just take off?
Request new data. The new runway may have a different "T" or special procedure. As well as an obstacle that may affect EVERYTHING from 2nd segment all the way to 4th segment profile requirements as well as the need for a full blast versus a reduced/flex.
Of course, much of this is predicated on WHO provides the TOLD info, and how much the company pays for it. At one of my employers, almost every runway had a 500' accel height, assuming no terrain/obstacles. But we ALSO had A LOT of "T"'s/specials. It ALSO gave the planes higher payload capability, especially hot and high that other operators DIDN'T have.
Then, they got another data vendor, accel heights went to 1000', FEWER "T"'s/specials. However, it seemed that SOME airports took a payload capability hit.
Originally Posted by
cardiomd
about cleared B1 instead of B which shortens runway by 400 feet, re-compute, or just verify and take off? That is the scenario I was envisioning.
See above, recompute. However, in the reverse, when you get a LONGER length available, at 4 employers I've never had to recompute, although it can get a little "complex", see below....
Originally Posted by
cardiomd
, if taking off at a longer runway do you recompute / flex to save a few dollars or just go?
Well, it can depend. AGAIN, who's providing the performance data? Let me give an example from a former employer;
IAH, 15L. Full length, we had a HIGHER accel height. Intersection departure, a LOWER accel height. Seems backwards, doesn't it?
The reason was, full length, and you started a left turn (pretty standard) and lost an engine AFTER V1, there's all the hangars in the way, hence the higher accel height, when a turn can be initiated. The data (at that time) computed that had you taken the intersection, you would be FARTHER down the runway, past the obstacles, and therefore STILL inside the TERPS trapezoid and safe to start a turn at a LOWER accel height if experiencing an engine failure after V1.
And if I'm not mistaken, that Kalitta airplane in Belgium had in issue relating to TODA, versus where they started the take off roll due to the taxi way-runway layout. I'd have to go back and read through the info again, but I believe that little amount would have ACTUALLY prevented that thing from going off road and having a hull loss.
Originally Posted by
cardiomd
Regarding recomputation, perhaps wind component could change and wouldn't want to use old data too if slight changes in runway length, or obstructions factored in despite identical heading?
Again, it "depends". Does the specific operator as well data provider allow for a "credit" when it comes to winds?