F flat dorian is, in theory, a playable mode, but it is not very practical. We looked at the F flat major scale (for the sake of thoroughness) so it is worth mentioning in this post what F flat dorian technically is, but it is probably not worth writing it out in every position.
The reason why it is not practical, is because it is theoretically a mode of Ebb (E double flat). Since we have not covered the key of Ebb in the major scales posts, it is probably not worth going into the modes of that scale.
The main thing to remember, is that F flat dorian is enharmonically equivalent to E dorian.
So, from a practical sense, in the unlikely event that you ever need to use the F flat dorian mode, just think of E dorian!
Let’s look at the notes in Fb dorian, but not illustrate the positions:
Fb – Gb – Ab – Bbb – Cb -Db -Ebb