V1
I was about to answer a question on a different forum about aborting a take-off due to a passenger event. I realise I can't remember what the V speeds are for.
Looking on the Internet gives a mixture answers relating to two separate constraints. The first is the speed that allows you to take-off with a single engine failure. Below this you must stop. The second constraint is the speed which is highest you can stop within the length of the runway. When these are the same, you have the maximum weight for the runway in question, but in general they won't be unless you de-rate. So what are the two names for the two different speeds? When you call V1 what are you saying - you can continue or you must?