das Uber Soldat, what you propose, having an elctronic backup is what I read in a FAA paper I found on the net. They are considering this option, not legal yet but if the yanks do it first ? ?
HOWEVER, one thing that I did read was that in considering allowing the use of EFB (Electronic Flight Bag) was that the device was then considered a piece of air navigation equipment and ONLY to be used as such. The paper was referring to off the shelf laptops so one would assume that has to encompass the iPad.