How did we get from "mentorship" to "CFIing from the back seat"?
BTW, there are plenty of CFIs who provide instruction in airplanes that have a back seat but are not dual control. Mostly WWII fighter types, like P-51s, Corsairs, Sea Furys, etc. While there are dual control versions of some of those fighters, the vast majority of them are not. Such a practice is completely legal and loggable.
Taking it even further, as a military instructor I can log IP time if I'm not even in the same aircraft as the student. If he is solo (ergo, not qualified in the aircraft but "signed off" to solo), and I am providing in-flight instruction over the radio, that is completely loggable.
I don't see why it would not work the same way from the back seat of a 172.
The thread went from mentoring to back seat CFI-ing (wow, I just made a word) when JrsyGuy asked if the mentor was a CFI, could they log the time? Also, I kind of combined this and another thread in my response about back seat CFI-ing.(There's been a few more posts about this lately.)
From what I've seen from green-under-the-wing pilots and from things I did as well in my training, I don't
think it's a good idea to have a CFI in the back seat with no control over the aircraft if something did go wrong. I personally wouldn't want to put my certificates on the line to train someone, and then have something go wrong and not be able to do anything to save myself.
You mentioned about people giving instruction from the back seat of "WWII fighter types, like P-51s, Corsairs, Sea Furys, etc." without any dual controls. I really don't think these are student pilots climbing into these high performance machines to get their initial ratings. These are pilots with some time under their belt (I presume).
As I have no military experience myself, I have no clue what is legal and what is not in regards to logging flight time. Adding to that, I think that's really an outstanding
accomplishment for you to be a military instructor. I applaud you for that. At the same time though, the people that make it into military flight training have been previously screened and tested to even make it to training. You have to already have a head on your shoulders to even sit in the cockpit. Because of that, I can understand being comfortable instructing from a back seat with no controls. I would trust those people with a lot more than I would an 18 year old kid right out of high school who hasn't even been in an airplane before. From what I think I understand you can't really compare military training to GA. It's two separate worlds.