Sorry, John-Alan, but I don't agree with your interpretation. I think you are looking at the technical definitions and missing the underlying purpose. Let me try to explain it this way - V1 is also called 'descision speed' because it is the point at which the decision to take off or abort is taken out of the pilots hands. One of the many factors that influences the selection of this speed is the runway - if the pilot suspects that the length, or the condition, or the aircraft load might be a factor, then they do the balanced field calculations and either limit that take off weight or lower V1 as required. If, as with the OP, you are letting the FMC calculate the V1 for you, it will take account of the runway length and condition. You can prove this for your self by selecting a shorter runway to start with and then looking at the effects on V1 of changing the condition from Dry to Wet, or by reducing the runway remaining.The accelerate-stop distance used in the definition is not defined directly, but it is used in a context which gives a definition. The full sentence is "to stop the airplane within the accelerate-stop distance". In this sense, that could include taxi-ways and runoff areas that are in line with, but not part of, the runway. The FMC will not include these areas in its calculations which is why the aircraft manufacturers give the pilot the option of overriding the FMC calculated V1 speeds with their one of their own.

Edited January 19, 201214 yr by Paul_Smith

Sorry Fabo, I don't quite follow you. When talking about a situation where we might not have an excess of runway (as here), you take the fugures you get from the PI section of the FCOM, and you cross check them with the tables in the PD section of the FCOM to confirm the actual (or effective) field length available.

GS depends on the wind and you should be taking off with a headwind, which will give you a lower GS. For jets you need to check the graphs to see if you have enough runway depending on a lot of factors, weight, density altitude, etc., In FSX it's not a problem, just fly the thing off

Maybe someone mentioned this already, but in a no-wind situation, at a high altitude your GS would be higher than you IAS, no?

Paul, first of all as an aerospace engineering student* I am indeed probably approaching this issue from a different angle than you are, since you are coming from a pilot angle, but I think you are also missing an underlying purpose:If you reject at V1 you should be able to stop the plane on the runway, this is true. However if you suffer an engine failure 1 second before V1 you should also be able to reach 35 feet AGL within the takeoff distance available on only 1 engine (past the point of failure). If you are limited by the length of the runway (as you appear to be at La Paz), you can only achieve this if the accelerate-stop distance is equal to the accelerate-go distance (and both are equal to the length of the runway). For a given set of conditions this will correspond to 1 and only 1 V1 speed. If you reject at a higher speed, then the accelrate-stop distance will be greater than the accelerate-go distance and you will overrun. If you continue from an engine failure at a lower speed, then the accelerate-go distance will be greater than the accelerate-stop distance and you will also overrun.Once again, I'm talking about the limiting case where your balanced field length is exactly equal to the runway length. If you have more runway available than you can indeed play arond with V1 and the above won't necessarily be true. E.g. if you have 1000' excess runway, it doesn't matter if your accelerate-go distance is 500' longer than the balanced field length and the accelerate-stop distance is 500' shorter.V1 will only guarantee you stay on the runway if the runway is equal to or longer than the balanced field length. If it is shorter you could indeed select a V1 that will guarantee you stay on the runway if you abort, but then you will be in trouble if you suffer an engine failure just before V1, since you will be 'too fast to stop, too slow to fly'. V1 is the maximum speed at which you can stop, but it is also the minimum speed at which you can go (in a field length limited situation).From the OP's post, it seems that the FMC will not protect you against the runway length being less than the balanced field length.*Not trying to imply I'm more knowledgable, just trying to show from what angle I'm approaching the discussion.Spin 737, with no wind your GS = your TAS, which at high altitude is indeed higher than your IAS (unless the atmosphere is seriously not behaving according to ISA and I'm not even sure if that would be physically possible), but as a rw pilot I'm sure you know that :)

To get some realistic numbers for La Paz, I tried running a takeoff performance calculation using TOPCAT, but it won't calculate takeoff performance for airports above 10,000 ft.As a "second best", I did a calculation for Quito (elevation 9,175 ft, but note that it only has 3,120 m of runway compared to La Paz's 4000 m). Conditions are zero wind, 15 degrees C, 1013 hPa, runway 35, 737-800.Interestingly, the optimum flap setting for takeoff is flap 1. The weight limit is 61626 kg (a huge margin under MTOW), and the V speeds under these conditions are 143/144/145. The takeoff is field limited, and the margin is 114 m.Flaps 5 and above lead to lower V speeds, but they are climb limited (due to the surrounding terrain, no doubt) and have lower limit weights.It would be interesting to see the numbers for La Paz -- despite the longer runway, the weight limit will probably come out still lower than for Quito.-----Martin Boehme

Flaps 5 and above lead to lower V speeds, but they are climb limited (due to the surrounding terrain, no doubt) and have lower limit weights.It would be interesting to see the numbers for La Paz -- despite the longer runway, the weight limit will probably come out still lower than for Quito.-----Martin Boehme

Also at airports like La Paz, climb out and engine out performance has to be calculated. I would hazard that if one was at max auw for a La Paz T/O, performance would be critical. I don't believe there is a Noise Abatement Procedure there, in which case that would allow for a shallower initial climb out in order to achieve and maintain safe EO speeds.vololiberista