CRITICAL ENG ON A JET.
Lets use a 747-400. Engs are numbered 1>4 L to R as you sit in the cockpit. Taking off on a runway heading N with a max crosswind component coming from E will mean that eng 4 is the critical eng for takeoff. Why is this? Because on T/Off you need lots of left rudder imput because the wind is blowing the tail to the L and the nose to the R. To counter the nose to the R on the roll you put in L rudder. Now number 4 eng fails on the roll meaning that numbers 1/2 engs are pushing the nose R and more L rudder is required to keep straight along the runway. If your speed isn't reasonably fast you will not have a very effective rudder and you may be at max L rudder imput and still be going right and off the edge of the runway. The answer would be to reduce power on the other engines to reduce the assy effect as produced by eng no 4 quitting. Of course eng 3 would also be a problem, but not being so outboard it is not such an assy problem and if 1/2 eng failed it would help reduce rudder imput required due to the wind.
Hope you got all that.