And you want them to shoot planes now? Or why post it in the skins forum?
Tracers are meant to be visible though.
- To see where you're shooting
- To see that the ammo is almost empty (different tracer color)
etc.
Today we even have so called dim tracers that are meant to be visible only by night vision equipment.
You can read about them here:
http://en.wikipedia.org/wiki/Tracer_ammunition