As of amendment 42(1978)of FAR 25-127/129..the introduction of VEF(formerly used on the flight test card)was made known to the pilots.VEF is generally one second prior to V1,but is called by the Constructor(with the DC10/B727 it could be as high as three seconds prior to V1,due no yaw promt for 'Recognition'..
So it's generally one second prior to V1 for the pilot recognition,to react by V1...
And it's two seconds added to the failure at V1 thence the stopping actions for the Accelerate/Stop DISTANCE
check the reading of the the two seperate FAR's(a)V1 definition,and (b)accelerate stop distance....
Cheers....
Balanced field length(as described above)hardly applies these days due to improved brakes,and the availability of \'Clearway\'..
If,for a given weight,one can stop (after the failure)on the runway one doesn\'t have to cross the end of the runway at 35\'...
With \'clearway\'one need only cross the end of the clearway at 35\'....
The T/O distance stipulates that half of the distance ,from L\'off to 35\'
,need only be over runway.....
