The irony is, there's pilots here arguing with an 18,000 hour captain...

Too true, I'm taking your word for this Rónán.

I guess the FAA is wrong then as well as every airline is doing it incorrectly according to you then. You are swimming against the current here. V1 is decision speed and the pilots decision to abort or continue will always happen before Vr, even 1 knot is ok. Ultimately anyone can abort any time they wish but they will be outside the bounds of their performance charts and against Airline SOP if they do so after V1. Unless the airplane is unflyable, and that is the only reason. BTW V1 does not apply in a Cessna 172. V1 only applies to part 25 aircraft with "guaranteed performance". V1 is based on ballance field length which is a performance chart and Vr is based on the stall speed of the aircraft more or less, this has everything to do with flying and flying here can not be overlooked because this is what is going to happen when you rotate and aircraft. The performance charts allow you to loose an engine after V1, even 1 knot after and still make 35 feet over the end of the runway. So flying has EVERYTHING to do with it.

As I see it, Joel, you have failed to take into account a few days back, that V1 can not be physically higher thatn Vr for the reason that you can not (think of it as physically can not) reject take-off as soon as you rotate.Your argument with Cessna (lets say a light 737) on a long (lets say longer) runway would be valid, V1 could be higher than Vr is NOW, but you WILL have to rise the Vr for that.This is sometimes done, to provide better climb performance, but only when you are climb limited, not field limited, as in both ASDA is higher than ASDR (accelerate-stop distance, for when you reject at V1 speed and then stop) and TODA is higher than TODR (take-off distance; for when you fail an engine at Vef and continue to take-off to be at certain height over the end of clearway - that 15ft or 35ft of 15m, I honestly am not sure now).This is primarily about higher Vr and V2, and V1 just follows the Vr though. Come to think of it now, you could do it if your original ASDR=ASDA, and TODR<TODA, then you would keep the V1 same though. As I understand it, you can trade runway for climb performance by making Vr and V2 higher either to the point of beind TODR=TODA or being otherwise limited (it was mentioned that Vlof must be lower than tyre max)

if you would read my last post you would Understand that I do know that V1 can not be grater then Vr.I know exactly why (unlike many that don't)based on claims here at the Forum , V1 was the question of RW length only (not enough RW to stop behind that point - 2 seconds after passing V1)then I raised the question what happen if the RW is longer then your Vr with still lot's of RW to stop if one wishes.every one failed to answer that question with a logical explanation apart from saying "this is the rule"unfortunately Robin was the only one to hit the spot with an Answer that I believed was the answer.he was the only one that explained that RW could be the factor but if it is not, then it is a pure decision point/phase of the take off run regardless to the RW.everyone else was stuck either that it is a RW issue or it was a pure decision phase, no one said it was combined apart from Robin.I was trying to prove to you guys that V1 is not solo depended on RW length as was claimed here at the beginning of that thread.no one even payed attention to my question(s)"Define V1"

Joel, I see that you understand it now, I was just elaborating on the premise."define V1" is not the best question. Definition, calculation and relations to other numbers are three different parts of "it" that is V1 in context of take-off performance. You see often in mathematics and similar sciences that definition and calculation are different animals.

ohh, definition of rule/subject , is the 1st thing before everything.1st you need to know what it is and the definition of the subject.only then you could determine the rules.if I would tell you that the definition V1, is a boy buying a chary pop stick. we would never ever talk about aviation (that is an extreme example to sink the point in) .we would talk about maybe the size of the pop stick, or the temperature it should be kept, etc.Definition is the base thing before everything.the basic question I asked guys here, "define V1", no really could.that is why it was so dragged here in this thread.Only Robin got the point and understood where I am aiming with those questions and he hit the jackpot.

Hi Joel,Sorry to be banging on, but what is wrong with the official definition?JAR/FAR 25.107(e) VR, in terms of calibrated air speed, […] may not be less than:• V1,• 105% of VMCA• The speed that allows reaching V2 before reaching a height of 35 ft abovethe take-off surface, or• A speed that, if the aeroplane is rotated at its maximum practicable rate,will result in a [satisfactory] VLOF”

those are the rules already, but not the definition.can you tell me the definition of V1 based on what you just posted?

Sorry, but that was for VR.“JAR/FAR 25.107V1, in terms of calibrated airspeed, is selected by the applicant; however, V1may not be less than VEF plus the speed gained with the critical engine inoperativeduring the time interval between the instant at which the critical engine is failed, andthe instant at which the pilot recognises and reacts to the engine failure, as indicatedby the pilot's initiation of the first action (e.g. applying brakes, reducing thrust,deploying speed brakes) to stop the aeroplane during accelerate-stop tests.”so basically before V1 you can safely stop on the runway in case of an engine failure. It also takes reaction time into account

V1 is defined as the takeoff decision speed/safety decision speed. There is no other definition for it.An example:You are below V1. You have an engine failure. You have an option: stop or go? Statistics show a GO is safer under this condition.You are below V1. You have an engine failure/fire. You would STOP in this condition - a fire in flight could be deadly.You are AT V1. You have an engine failure. You have an option: stop or go? Statistics show a GO is safer under this condition.You are AT V1. You have an engine failure/fire. You would STOP in this condition - a fire in flight could be deadly.You are 2kts above V1. You have an engine failure/fire. You would GO in this condition - stopping now could result in an overshoot.There was an accident with a Boeing 707 years ago. They suffered an engine failure at V1. The decision was taken to reject the takeoff. By the time they set idle thrust and started braking, they were 30 kts over V1. The aircraft required 7000 ft for the takeoff. They had 12000 ft ahead at the start of the takeoff run. They ran off the end, collapsing the gear. The crash investigators discovered the aircraft was 4 tons over MTOW. They did a computation - at 4 tons over MTOW at the actual reject speed, they calculated they needed 15000 ft to stop from the rejection point.Best regards,Robin.

The legal defintion of V₁ is provided in the applicable airworthiness regulations. In the U.S., that is Title 14 of the U.S. Code of Federal Regulations. The definition for V1 can be found in part 1, section 1.2 (http://ecfr.gpoacces...1.0.1.2&idno=14):V₁ means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V₁ also means the minimum speed in the takeoff, following a failure of the critical engine at V_EF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.Note that it is explictly and deliberately no longer associated with the term decision speed, critical engine failure speed, or any such descriptive term. That is to remove the question (and confusion) of whether it is the beginning or ending of a decision process. Action to stop the airplane must be taken no later than V₁ in order to have a high likelihood of achieving the certified accelerate-stop distance provided in the airplane flight manual. Some of the posters in this thread have stated or implied that the pilot does not need to take any action until up to 2 seconds beyond V₁. Although there are distance margins in the accelerate-stop distance, they were never intended to allow the pilot to delay taking action until after V₁.Robin, I hope you have a typo in your first example above. Depending on how far below V₁ you are when you have an engine failure (and on the type of engine failure you had), you may not be able to attain a height of 35 feet by the end of the available takeoff distance. For your examples of an engine failure or engine failure/fire at V₁, you are very likely going to exceed the certified accelerate-stop distance. Unless the pilot believes the airplane is unfit to fly, the takeoff should be continued for an engine failure at V₁. (If the failure occurs at V₁, you would have exceeded V₁ by the time you can take the first action to stop the airplane.)Joel, for your benefit, yes one could conceivably stop an airplane within the runway length (if the runway is long enough) if the reject is initiated above V_R. However, to stay within the confiines of the performance data calculated for any particular takeoff, one must operate the airplane according to the assumption contained within that data. At V_R, the piilot is to initiate rotation. SInce the acclerate-stop distance data are based on initiating a reject with all wheels on the ground, there is no longer any stopping distance data by which the pilot can definitively say they complied with the accelerate-stop distance requirements. Showing that an airplane can begin rotating to the takeoff attitude, and then at some point (before liftoff? after liftoff?) safely stop on the runway is not something that is tested during airplane certification. Once the rotation is started, it is assumded that the takeoff will be continued. Therefore, V₁, which is the last point at which a rejected takeoff should normally be initiated, cannot be higher than V_R, irrespective of runway length.Don Stimson

Donstim, that 2 seconds seem to be either the difference between JAA and FAA, or indeed an older application of the rule.Either way, while it does not explicitely include rules about Vr in the definition itself:

V 1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

but as stated by Don, you can not put V1 after Vr, for practical reasons. Again, if you do have ample runway, you can make Vr higher, and, by extension, V1, too.That is not against definition, even if you argued you could stop within ASDA, even if you rejected at V1+10, because you should have been rotating and/or flying at that time. You cant take the first action after you lift the nose gear up, that would most likely end badly.I do have a feeling we are talking the same around and around, Ronan, Robin, then me and Don and several others. But let it be, for the benefit of readers. I have learnt much from similar discussions in past.

Akila !!The Boeing FCOMS come free with the NGX.It's time you started reading them I think.Fred.

Donstim, that 2 seconds seem to be either the difference between JAA and FAA, or indeed an older application of the rule.

JAA (EASA) and the FAA rules are now the same. Between 1978 and 1998, the U.S. certification regulations included 2 seconds of continued acceleration after V₁, but that was not intended to be used procedurally such that pilots would conciously delay action until after V₁. It was just to add distance margin for safety reasons.Although the definition of V₁ itself does not refer to V_R, the requirements quoted above by Martin (which includes the requirement that V_R may not be less than V₁) apply.Don