I have a data set that looks like this:

LA BEL: M_FRONT _HEIGHT
Po ints Taken: 1
Actual Nominal #NAME? #NAME? Dev Out/Tol
Y: 1808.608 1808.8 1.5 -1.5 -0.192 **********


LA BEL: M_REAR_ HEIGHT
Po ints Taken: 1
Actual Nominal #NAME? #NAME? Dev Out/Tol
Y: 1808.3624 1808.8 1.5 -1.5 -0.4376 **********


I want to delete all the rows except those that have Y: in the first column.
How would I do that? Everything I have tried so far has only deleted some
of the rows, but not all.