I tried posting this in the AVSIM Flight School forum...I have a question about the V1 speed. I understand that V1 is the "go/no-go" decision point of the takeoff roll, and I am familiar with how V1 is calculated (Weight, wind, surface condition, etc).Years ago one of my flight instructors told me that V1 is "the maximum speed at which there is still enough runway to reject the takeoff". But I am hearing otherwise. Some tell me that runway length does not affect the V1 speed, and that rejecting a takeoff above V1 is not safe for reasons of "directional control", not runway length remaining.IF a B737 attempts a departure from a 12,000 foot runway but suffers and engine failure after V1 and before Vr, they may still have 5 or 6 thousand feet of runway remaining...Kenny Rogers

The V1 speed in commercial (Class A) aircraft operation is the highest speed at which a take-off can be safely aborted in the runway length remaining, and also the lowest speed at which the take-off can be safely continued with one engine inoperative.The V1 speed must allow for sufficient runway to be remaining to bring the aircraft to a halt using the brakes only (no reverse thrust).Part of the calculation is that the ASDR (Accelerate-Stop Distance Required) must not exceed the ASDA (Accelerate-Stop Distance Available), assuming that the ASDR is the sum of:(a) The runway required to accelerate from a standing start to the V1 speed(:( Continued acceleration from the end of (a) for 2 seconds with all engines operating© Maximum braking to a stop using the brakes only, assuming that this retardation does not commence until the end of the period in (:( above.V1 cannot exceed Vr, but it is often equal to it. Like you say with a 12,000ft runway, a loaded 737 will have no trouble stopping even up to Vr, so V1 = Vr. When runway length is limiting, V1 may reduce. Aircraft Weight, Thrust Usage, Surface Conditions, Wind, Slope, etc... will all have an effect on this.The above is all JAR-OPS stuff... the feds might (and probably will) do it a bit differently.

Thank you very much!Kenny Rogers

Most commercial operators also have airport analysis charts that allow the aircrew to determine their allowable MTOW for a given runway. This is so they remain within the V1 runway remaining criteria.Cheers,JohnBoeing 727/737 Mechanic

>the takeoff". But I am hearing otherwise. Some tell me that>runway length does not affect the V1 speed,Kenny,You are right. I am not sure why people do not state it explicitly but in fact V1 does NOT depend on runway length - or does not depend to the degree one would expect. The runway length is always assumed to be enough to execute legal takeoff. But whether the runway is 8,000 ft or 20,000 ft you will end up with same (or almost the same) V1.V1 calculation assumes so called "balanced field". What does it mean ?It means that runway required to stop the airplane equals the runway required to get airplane airborne assuming one engine just failed. So when you reach V1 you are at the "equilibrium" point - both stopping the airplane and continuing takeoff (even when egine failed) entail the same 'price'. Michael J.

Kenny,Basically you are talking about

Quote "Some tell me that runway length does not affect the V1 speed, and that rejecting a takeoff above V1 is not safe for reasons of "directional control", not runway length remaining."That sounds like they were discussing "Vmcg" or the velocity minimum for controllability on the ground. A factor affecting multi-engine aircraft with the loss of the most critical engine. If you are below this speed, asymetric thrust set at takeoff power can cause the aircraft to loose directional control until you retard the power, ie reject the takeoff. This speed cannot be above refusal(V1) or you will enter into a deadmans zone, beyond V1 and unable to keep the a/c straight on the runway.

>>The above is all JAR-OPS stuff... the feds might (and probably>will) do it a bit differently.The feds (i.e., U.S. FAA) "do it" the same as the JAA (at least for dry and wet runways), but the requirements you've quoted are actually from the transport aircraft certification requirements prior to Amendment 25-92 (FAA) and JAR-25 Change 15 (JAA). The new requirements replace the 2 seconds of continued acceleration after V1 with a distance equal to 2 seconds at a constant V1 speed, add wet runway requirements, and require that the stopping distances be based on wheel brakes that are worn to their replacement or overhaul limits.Note that for a non-limiting runway length, their may be a range of V1 speeds that would meet these requirements. The operator may choose from within this range, keeping in mind that a lower V1 speed provides additional safety margin for a rejected takeoff, while a higher V1 speed provides a shorter takeoff distance.Don S.

Actually, the V1 calculation does not assume a "balanced field." The balanced field V1 usually provides the highest takeoff weight capability for a given field length, but there may be good reasons to choose an unbalanced V1 -- V1 limited by either the rotation speed or the minimum control speed, a close-in obstacle that necessitates minimizing the takeoff distance, use of clearway or stopway, or simply a decision to provide additional margin for either the stop or go distance.Don S.>>V1 calculation assumes so called "balanced field". What does>it mean ?>It means that runway required to stop the airplane equals the>runway required to get airplane airborne assuming one engine>just failed. So when you reach V1 you are at the "equilibrium">point - both stopping the airplane and continuing takeoff>(even when egine failed) entail the same 'price'. >>Michael J.>

Thanks all!Kenny Rogers