Ace Combat 4

I am trying to find the special planes, and so far i have most of them, i just cant find the f117!

i know it is in level 16, but i dont know where. Do you have to do something to trigger it? i've killed the f-2 above the crater, i've killed the formation of f117's and their f22 escort, and the SR71.

where and when am i supposed to find it?

thanks