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Guest Jeroen November

General V1 question

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Guest Jeroen November

Hi all,Is V1 in all cases the speed at or above which a TO has to be continued? I'm just imagining a nearly empty 747 on a long long runway. Because of the low payload V1 will be lower & reached pretty quick & thus there could be still a lot of usable runway available to stop(correct?). Or is runway length allways incorporated in the calculation and for the same payload V1 would be greater on a longer runway?Greets,Jeroen

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Guest tmetzinger

>Hi all,>>Is V1 in all cases the speed at or above which a TO has to be>continued? I'm just imagining a nearly empty 747 on a long>long runway. Because of the low payload V1 will be lower &>reached pretty quick & thus there could be still a lot of>usable runway available to stop(correct?). Or is runway length>allways incorporated in the calculation and for the same>payload V1 would be greater on a longer runway?>>Greets,>>JeroenHere's a reply on an aviation forum to a question similar to yours:----------------quote begin----------------------Firstly, let us refresh what is V1 for the benefit of non-aviators. To a pilot, V1 is also known as the decision speed - meaning, a speed reached during the take off when he must make a decision to either abort or continue the take off safely in the event of an engine failure. So, if an engine should fail at the decision speed (V1) during the take off, the pilot is offered two safe courses of action: He can choose to continue the takeoff on the remaining engines or elect to stop the plane by applying full braking. Either way is safe. For calculation and performance sake, the take off distance starts from the point the take off run is initiated to a point when the aircraft has reached 35 feet. This is also known as the balanced field length. Hence, the decision speed (V1) is used in such a way that the sum of the distance required to accelerate to V1 and then decelerate to a stop is the same as the total distance when the takeoff is continued following engine failure.Thus, it is a normal practice that, should an engine fail before V1 is reached, the plane is usually brought to a stop on the runway, whereas, if an engine fails at a speed greater than V1, the takeoff is continued. Why can't one stop after V1 if the runway is long? Well, overwhelming number of accident statistics have shown against such a decision. Yes, a long runway may physically give the pilot that comfort, but legally he should follow the rules regardless of the runway length. Even before departure, a pilot knows how much runway he requires for the take off. There are no markings on the runway where he must look out in relation to the V1 as the performance is precisely calculated. If the calculations indicate that the balanced field length is insufficient for the particular aircraft weight and surface temperature, then the payload must be reduced in order to take off safely. There is of course a relationship between V1 and runway length. The higher the V1 (so would the VR and V2), the longer the runway is required. I know you are trying to find out why one shouldn't abort after V1 even if the runway is longer than the balanced field length. Well, this is against conventional wisdom. The chances of a disaster are greater than continuing with the take off after the decision speed. Continuing will enable the pilot to climb to a safe altitude, sort out the emergencies and return for a safe landing. ----------------------quote end--------------------It is generally accepted that trying to abort a takeoff past the V1 speed is more dangerous than taking the problem into the air. Remember that kinetic energy (that must be lost through braking or, god forbid, impact) increases as the SQUARE of velocity, so every extra knot of speed is a lot more energy to lose.

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Guest Jeroen November

Thanks for the reply Thimothy....but let's theorise. You're in you're TO roll at ot just above V1 in your 737 & there's (god forbid) a dual engine failure. You're nog going to tell me that you're going to continue the TO assuming that a safe climb can be initiated without thrust from either engine? Or is the V1-rule only applicable if there are functioning engines available? Reading your quote there are apparantly a lot of pilots that (unfortunately) neglected this rule in the past... strange in these days of rules & regulations.Greets,Jeroen

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Guest tmetzinger

>Thanks for the reply Thimothy....but let's theorise. You're>in you're TO roll at ot just above V1 in your 737 & there's>(god forbid) a dual engine failure. You're nog going to tell>me that you're going to continue the TO assuming that a safe>climb can be initiated without thrust from either engine? Or>is the V1-rule only applicable if there are functioning>engines available? Reading your quote there are apparantly a>lot of pilots that (unfortunately) neglected this rule in the>past... strange in these days of rules & regulations.>>Greets,>>Jeroena DUAL engine failure? of course continuing a takeoff at that point isn't an option, as you don't have an airplane anymore, you have a big hunk of aluminum and you may be along for the ride depending on if your hydraulics survive the failure.That said, the odds of a simultaneous dual engine failure in a properly maintained transport jet are astonomically low.

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>Thanks for the reply Thimothy....but let's theorise. You're>in you're TO roll at ot just above V1 in your 737 & there's>(god forbid) a dual engine failure. You're nog going to tell>me that you're going to continue the TO assuming that a safe>climb can be initiated without thrust from either engine? Or>is the V1-rule only applicable if there are functioning>engines available? Reading your quote there are apparantly a>lot of pilots that (unfortunately) neglected this rule in the>past... strange in these days of rules & regulations.>>Greets,>>JeroenI don't remember where I read it, bou I hope never to forget it. U don't reject a takeoff because an airplane can stop in the available runway, takeoffs are only a rejected because the plane CANNOT fly.In any case, dual engine failure in a twin is really bad, because u don't have any means of stopping...no reversers, no spoilers, no brakes, not even any flaps.

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Guest joediamond

>In any case, dual engine failure in a twin is really bad,>because u don't have any means of stopping...no reversers, no>spoilers, no brakes, not even any flaps.Every transport category aircraft has an emergency braking system to enable one to stop the aircraft without normal braking systems being available.The aircraft I currently fly uses a hydraulic accumulator which provides up to six braking applications without hydraulic pressure. The stopping distance will be greater as there is no anti-skid protection for the emergency system but you will still have a means to stop the aircraft.Additionally, if the APU is running for the takeoff, which is normal for us, then it would continue to provide electrical power even if both engines were to fail. The electric auxiliary hydraulic pumps would provide hydraulic pressure so you would still have steering and normal brakes.So while there is no way you could fly after a dual engine failure you certainly have the ability to stop.C McCarthy

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