Originally Posted by AerocatS2A
Air Rabbit, you are overcomplicating things. V1 is always different because weight is always different. Using a different V1 speed on different take-offs is normal regardless of whether there is a choice of V1s or not. The only thing that needs to be remembered is the V1 speed chosen for that particular take-off. I find it easy to remember because we bug it on the ASI.
On the topic of choosing a V1 from a range of speeds. This is also simple. We kind of do it in our company in that there is a range of V1 speeds available from our performance data, it is not really a choice though because the company has already decreed that we are to us the lowest V1 available. When we do the performance we have a V1 associated with our actual weight and a V1 associated with the max allowed weight for the conditions. All V1s in between are valid, we use the lowest, very simple.
Originally Posted by de facto
Air rabbit,
By the way these few lines were taken directly form Boeing Engineering on "range of V1".
So Jeez to you from me and the boeing guys.
I am fully aware that V1 is “always different” – and surely weight is big factor – but runway length, temperature, tailwinds, etc., all get thrown into the mix. I don’t have ANY problem with selecting a single V1 that is within that range of legitimate V1 speeds (emphasis on “legitimate”), and then using that valid, singular, V1 speed, the way it was intended to be used. My post was to question whether or not we were launching, yet again, on the theme that pilots should have the ability to select whatever V1 they wanted to use … some were saying that they regularly use a V1 speed that is a significantly less number than the computed V1, simply to ensure that if a problem occurred, they would have sufficient runway to stop. Others said they often selected a V1 speed that was significantly higher than the computed V1, this time however, to ensure that if a problem occurred, they would have sufficient runway to safely continue the takeoff. The fact is, if one of those two values IS, in fact, selected, and the problem that actually occurs mandates the “other” action, the result would likely be less than optimum.
If your company uses an approved method, regardless of that method, to determine a single V1 speed (again, a legitimate number), if a problem were to occur, the proper action taken would allow either the safe rejection of the takeoff OR the safe continuation of the takeoff – regardless of where, during the takeoff, that specific V1 speed is reached, I'll have to eat my fair share of "crow" - its not fun, but I've done it many times before ... actually too many! Almost any pilot will likely confirm that experiencing a problem during takeoff on 15,000-foot runways is not a huge problem regardless of what decision is made. But IF the runway is one of those that gets a bit more performance critical, ANY tendency toward a more cavalier approach to the decision of whether to GO or to STOP is infinitely more important. Hindsight is only valuable to those who are here to recognize it. The very best way to ensure the safest of outcomes is to use the proper decision making on EVERY takeoff on EVERY runway ALL THE TIME. V1 is NOT a decision speed. V1 is the point at which that decision must have been made – note the past tense - and action initiated - whether to Go or Stop. It is intended to be the point from which a continued takeoff can be safely conducted or the point from which a rejected takeoff can be safely conducted – depending on what decision had been made (and already in action) when the airplane reaches that specific airspeed. If your company procedures provide a V1 “range” … fine … I guess. I’ve not seen any such “ranges” being spit out by any computer or offered in any book or manual, but I have been out of the day-to-day grind for about a year now (with my time largely spent on issues involving training or simulation matters) and perhaps V1 speed ranges are becoming more prevalent – although I would still argue that within that range – the flight crew should select ONE speed and treat it as the defined V1 speed. If V1 speed ranges do exist, then it must be true that any number within that range of numbers MUST have been determined to provide the same airplane performance (either continued takeoff or rejected takeoff) and do so within the runway remaining at the point the airplane reaches any specific speed within that range. If that is true and a specific number is selected and used the way V1 is intended to be used … I’ll not argue with that.
While it probably doesn’t make any difference to some here (insults notwithstanding), the fact is that I personally know quite a few folks at Boeing (including some who were at McD previously) – and several other manufacturers as well – some of them for a good majority of my professional career. None of them would disagree with what I’ve said here - as what I've said is the way I was originally trained and the way I have always conducted training or evaluations. If you are interested in additional information on this particular subject, I would recommend the “Pilot Guide to Takeoff Safety,” which is available for a fee from the US National Technical Information Service in either hardcopy or microfiche. Their website is here:
NTIS - National Technical Information Service