Takeoff and landing distances - fact vs. fiction

Right moemnt for the topic but adding 30% or 50% to PoH numbers is not new? it is stated in the PoH that one need to compensate +××%, probably less obvious on FF calcs but who does really think C182 does 600ft on takeoff?

On runway state, they should have at flown the opposite runway and mix ground roll numbers to at least cancel any slope or curve effects

The big elephant is turbulence: there are no adjustments for gust factors or turbulence from surrounding terrain in POH numbers for 50ft obstacle distances (these are flight tested on clean terrain while in reality anytime there are obstacles there is turbulence, not necessarily from the same obstacle), the adjustment factor for wind gradient or wind sheer is less understood can go easily from 110% to infinity unlike other effects you hear about when talking performance that are well understood, especially when they are measured on “isolated ideal test runways” (e.g. density altitude, grass/wet surface, smooth wind…)

If you can’t takeoff in grass runways, it is probably the nearby trees and hangars on your crosswind not much what is under the wheels…

@boscomantico
Commercial jet aircraft never use full T/O thrust since it increases the wear on the engine.
There are two methods: Assumed Temperature and/or Derate T/O which is programmed into the FMC.
It is fairly easy to type in the wrong numbers (f.e. wrong (too low) aircraft weight). Then you will get a spectacular youtube video.

Happens quite often, esp. when flight crew suffers from fatigue which is quite common in these days:
https://en.m.wikipedia.org/wiki/Emirates_Flight_407

Without seeing the calculation it’s difficult to say what the numbers said. Without knowing their procedures it’s not easy to judge. They may have had a lowish V1 committing them to go. It could also have been a screw up.

What kind of calculations does this Foreflight do?

And also, scarily enough, the only requirement for a complete sudden failure of one engine at V1 is to make it above the far end at 35ft, with no margins added.

boscomantico wrote:

I wonder, even disregarding the 100 or so metres that were wasted at the beginning of the takeoff-roll: how is it possible, with our 1000+ regs that govern commercial carriers, with their tons of manuals and mandated runway margins… to have such takeoff happen???

Reminds me of several original 747 take off’s in the days when that plane was new. Pan Am out of ZRH with an engine failure, PIA without one, several freight(en)ers, also 707’s and DC8’s out of ZRH’s runway 28… Scaring the crap out of the mice living at the far end and being close to taking a few roofs of at Rümlang or Glattbrugg…. These days are mostly gone because apart from the A340 nobody is working with so few power anymore and with the A340 its intentional.

I can’t remember how the flexing works on the MD, I think there was a separate computer however, not the FMS which does this. Also there were selectable flaps. Both can go wrong if you are not careful. Slats were extended, otherwise he would not have gotten very far, but we don’t know what flap setting he had and what he ought to have had. Or wether he was simply too heavy and went for it anyway as he knew the ground roll would work out. Certainly an unbalanced take off, but that again is nothing special really.

The MD82 if I am not mistaken was a lot less powerful vs weight against the 83 and the short 87, which was a rocket.

boscomantico wrote:

Barry Schiff once did this. Here is a new, interesting little video:

Interesting video. However, it would be nice to know how the values calculated by FF compare to the ones out of the PoH in the first place.