Being a L-188 co-pilot I wasn't concerned with all the operational details. It was a cushy job. The FE was as busy as a one arm paper hangar shifting engine RPM's and electrical buses just before and after take-off and landing. I don't remember any APU info other than the screen over the hole at the back tip of the tail cone. The L-188 was the biggest source of hearing loss on the airline. On the ramp at ground RPM they were a screaming banshee. At TO power they were the quietest. In cruise flight, there was an RPM and Phase sync for all 4 engines to reduce mid-cabin noise. When the Phase sync was on, each propeller kept the same angle relationship with the ones adjacent that was pre-calculated to produce the least noise; a very temper-mental fancy gadget.