Originally Posted by
Intruder
So, your assertion that landing speed is the only variable is incorrect in reality.
Now just hold on a minute guys. At no time did I ever make an “assertion” that there is
ONLY one variable in determining landing distance!!
Go back and read my posts and you’ll see that I used the words “typically dependent” and “typically similar”. Landing speed is certainly not the “only variable” that affects landing distance. Oh, if it was only true.
Further, if you were to go back and read 4 of my posts (numbers 5,6,8, and 14) I even listed some of the other factors that would affect the results of landing distance determination, just to ensure (I thought) that no one would assume this could be an exact number. And even another thought, can different certification requirements have played in here too?
I’ve seen this happen before when only the last few posts are considered without seeing what’s already been stated.
The choices of different autobrake settings and the corresponding different landing distances obtained are not decelerating the aircraft at the mu value for the tire/surface. And it is at this mu value that the original posters minimum LDA runway would be attained.
Intruder, to be "pulled off the simple mu relationship”, as worded, can happen anytime braking is not attainable to the point of reaching the tire friction limit. Not your everyday occurrence. The original poster’s question seemed to be referring to normal ops, and it was with this in mind that I made my statements.
MFS’s data, normal ops, seems to fit even closer than I’d expected. For Intruder’s with the 747 not so at very high speeds. Why the 400, with winglets, has a higher approach speed than the 200 for the same weight? Don’t know. Does the “stuck stab scenario” or possible “brake torque limits” or brake energy limit introduce other factors? Outside of normal ops? A question for a 747 performance guru.