How do you add data from one element of several arrays into a new arrays?

For example:

You have:

SET DEFAULT TO C:\GRAPHICS
DIMENSION aTIF[1], aFJP[1], aPNG[1], aJPG[1], aIMAGES[1]

ADIR(aTIF, "*.TIF")
ADIR(aFJP, "*.FJP")
ADIR(aPNG, "*.PNG")
ADIR(aJPG, "*.JPG")

ACOPY(aTIF, aImages) ???

* At this point, how do you add the resulting FILENAMES only from each array,
* if there is data, into the last array, aImages?