V1 Min ... again!!!!
Ferrydude,
Thanks for the link that further explains the V1 concept. After reading this, I remember another enlightening tidbit that was discussed at this seminar.
V1...the definition thereof...is quite different from what I was taught. Boeing claims the FAA's classic definition is incorrect from the start...and that aircraft certified in the U.S. under FAR Part 25 were never certified under the classic definition (i.e. decision speed).
Instead, Boeing (as described in this seminar that was held for us in the early nineties) maintains that, from an engineering standpoint, the V1 is the maximum speed the aircraft can attain (thus, the maximum kinetic energy) and still be able to stop on the remaining runway.
In other words, the design braking capability of the aircraft is capable of dissipating only so much kinetic energy (for a set of given conditons)...and at V1 (for that set of given conditions), the brakes need "X" amount of runway distance to dissipate that amount of kinetic energy. On a takeoff where you're accelerate/stop limited, the amount of runway you have remaining exactly at the point V1 is reached...is the exact amount the braking system needs to dissipate that much kinetic energy.
To put it simply, if V1 is, say for example 135, and assuming the takeoff is field-length limited for accelerate stop, then rejecting the takeoff at 136 will cause an overrun. The braking capability is insufficient to dissipate that much kinetic energy in the runway distance remaining.
Or, to put it another way...135 is the "brakes on" speed. If the aircraft is allowed to accelerate above 135...and, again, assuming you're accelerate/stop limited...you won't be able to stop the aircraft on the remaining runway. It's physically impossible.
Now, I know the FAA says you have two seconds reaction time...and all that $#%^...but, according to the engineers at Boeing...and they spoke to us directly at this seminar...above V1, (even only one knot above V1) the aircraft has too much energy to get stopped on the remaining runway.
This is why they (Boeing) recommend and profess that the V1 call be made before V1...so that the pilots have sufficient time to react...to begin the RTO (and deceleration) process BEFORE the aircraft is allowed to accelerate above V1. Once the aircraft is allowed to attain a speed above V1 (maybe even only one knot above V1), the braking capability will be insufficient to stop the aircraft in the remaining distance of the runway. (Assuming, again, you're accelerate/stop limited)
Thank you, again, for your input. Again, I know little about the engineering/certification aspect of all of this. But, I do remember my old airline having several accidents related to this. And, this was why Boeing sent a team to 'educate' us. And, what Boeing had to say was (to me) startling. I guess it was an eye-opener to the airline management as well, because our SOPs changed to match Boeing's recommendations within months after this seminar.
Thanks again...
Tom