Collisions, why won't they work?

I am making a game in which you may fire guided missiles. The missiles are added to the scene via an empty. They track to the enemy plane. I am trying to use the collision sensor to end the missiles when they hit the plane, take a life away from the plane, and add explosion objects. None of the collisions seem to be registering.

Is the missile dynamic?

Er, does it have to be?

At least “Actor”!
Bye