If you have pilot incapacitation high speed rejects should not pose a problem because you're not going high speed. 80kts is a first check. If there is no response, you are in your mind already stop minded. If he doesn't answer your second inquiry (100kts ie), you stop. In most aircraft you are even below Vmc at this point. 1...2 seconds reaction time gives an extra 7-8kts acceleration. Let's say 110kts max at the point of reject. On the 737 Vmc is around 110kts. This means you're at the edge of its "controlled flight" envelope, and since you were stop-minded from the very first 80kts call, in most cases you will not even be at 110 upon initiation of the reject. Stopping at this point should not pose any problem at all. You are FAR FAR away from a high speed reject which, I agree, isn't the most fun thing to do with an airliner.
At high speeds it's designed to fly, you are go minded, at low speeds it cannot even control it on the runway if you were to continue and have an engine failure. There is indeed the "grey" area in between low and high speeds, but that's why the 80kts check IS a pilot incapacitation check as well, to PREVENT you go into the grey zone. So simply be ready for it.
SSG, V-speeds are not all based on runway numbers. Vr and V2 are weight based and because V1 cannot be greater than Vr, it is in a lot of cases weight based as well. It's not because you have a balanced takeoff performance, you're using all the runway available. It fits "into" the runway, yes, but you'll have extra room. If the runway in it's current state doesn't fit, you need to change something (bleeds off, higher flap setting, another runway for better wind conditions or longer length,...). V1 is something you can play around with, and runway length can be a factor.
There are some exceptions, ie improved takeoff where you use as much runway as possible (keeping in mind tire limits etc) to have a better climb performance when you are ie obstacle limited. It's the only case where I don't like the V1 numbers (sometimes very high on long runways), but I trust a very high speed reject can be done. With all the consequences: hot melting tires, probably a fire, maybe you block the runway, maybe you end up in the grass because life is not perfect (or the water). I've talked to people who have rejected takeoffs, and they all say: "the braking is hell, nothing you've ever experienced before". And RTO tests were performed with degraded brakes during testing, so in the end I presume it will work although some V1 values don't really give me a comfortable feeling.
Wet or contaminated runways? Well, V1 is reduced as well, and on contaminated runways pretty much based on Vmc. Things can be tricky because controllability is an issue for every speed. But 100kts is still a reject because it's below Vmc. You really need to be prepared for it in these cases.
Cheerz...
Ps: the 60/40 rule is a guideline for small single engine props where you simply have no decisions speeds. If you encounter a problem before using 60% of the runway, stop. Don't try to stop a little prop on less than 40% of the runway available. Funny someone claims a "PPL-we-have-no-rule-for-it-so-use-this-guideline" to be used on commercial jets as a governing rule...
ps2: heavies are usually runway or even "braking" limited, but the story remains the same: pilot incapacitation and high speed rejects should not come together. Either you reject low speed, or next calls are V1 and Vr, and it's a go anyway if he doesn't respond.
Last edited by BraceBrace; 16th May 2008 at 10:29.