You need to put your code in the chopper's initialization field instead, or else specify the chopper's name, not this, in the waypoint's code.
For example, if your chopper was named chopper, your code in the waypoint would instead be the following:
chopper flyInHeight 3000
As CrashnBurn pointed out, 3000 might be beyond the accepted value range. But, try it and see if it works. Just to let you know, I think 1,000 meters is a realistic HALO altitude, in terms of from what altitude real operatives jump. At least, that's what my brief research revealed.