IMHO, there are far too many CFII's teaching students to transition
from an ILS approach to a LOC approach midstream, if the glideslope
fails.

Human beings are very habit oriented. Things are much more consistent
if we do things the same way every time. (Watch a professional golfer
getting ready for a drive a few times, and you'll see that they do it
the same way every time.)

The prudent (in my opinion) action, when the glideslope fails inside
the FAF, is to go missed and then get your head around the LOC
approach, regardless of where you are on the Final Approach segment.

If you have yet to reach the FAF, brief the LOC approach if you have
time. Otherwise, ask to hold at the FAF (if available) or take another
action that will give you the time.

Just my two cents.

-Rob

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Rob Montgomery
www.scarylittleairplanes.org