When an aircraft gets upgraded avionics like a GPS, autopilot, and electronic flight instruments in a mid 1970s aircraft for example; is an aircraft flight manual supplement required and must it be printed and carried along with the aircraft or can it be in digital format? Same with the required manuals like a GPS quick reference guide, can that be digital or print? I’ve been debating this with a number of other pilots and have had conflicting answers, none can site their sources. I’ve also contacted AOPA, Garmin and another manufacturer. All those sources have told me that the AFMS and reference guides are required to be carried onboard in print form and it is not legal to have solely a digital copy. I’m a member of a flying club and the planes don’t have any aircraft flight supplement manuals and have been debating this topic with the club leadership. Do you folks have any guidance in finding the legal reference for this situation?