Odins,
The brightest of our readership can't seem to fathom that such letters are in fact being sent out. Calling any such action incomprehendable or something to such an effect is just indicative of the ostrich effect so many of the weak succumb to here. The truth is that they are being sent out and perhaps its just a question of time before you or others receive one.
While its entirely true that engine out taxi is not SOP... (DUH...) these warning are being generated by muppets with enough undeserved and uncontrolled power to eventually end your career should your record of non compliance get large enough. Perhaps they are looking for heads to hunt but I respect those individuals who won't bend over..however some do, and that just helps the muppets along in their game.
Just keep a resignation letter with you at all times and fill out the date when you've finally had enough...but NEVER sell out your self respect or dignity to these people.
It's not the company of 10 years ago.....