You pretty much need to chunk out three lines at a time, and drop them into the arrays in position 'i' for whatever iteration you are in.
A better option would be to use a collection though; arrays require manual resizing, and then you are splitting the data up between three separate arrays. Since the data has to represent something, you simply pull in three lines at a time, construct an object that represents it, and then provide that object to a list collection. Mucho easier than three arrays.
header('HTTP/1.1 420 Enhance Your Calm');