Originally Posted by
Vessbot
Whoa whoa wait, in your EPR planes is all that's available to synch off of, or did someone actually decide that that's a good idea?
On the 767 and 747-400 - with FADEC EPR engines - the autothrottle will align EPR across the wing (obviously with N1 engines it will align N1 across the wing). It's not possible to automatically align N1 with EPR engines with the autothrottle active (even if you try to manually stagger the throttles to align N1, the 'trimmer' will override the throttle stagger to align EPR).
On the 777/787, it is possible to align N1 with EPR engines and the autothrottle active, although it
may require manually switching the FADECs to Alternate N1 mode (not sure about that last part - it's been a long time since I worked the 777). That's not an option on the 767/747-400 - the autothrottle won't engage with EPR engines in Alternate N1 mode.
That being said, with FADEC EPR engines it's normally not much of an issue - there tends to be minimal N1 variation with EPR with FADEC. That wasn't the case with the old hydromechanical control JT9D-7. On the JT9D powered 767, the N1 'beats' could be super annoying for those sitting near the wing. The JT9D controls needed to manually adjusted ('trimmed') on a regular basis (every month or two) to adjust the stator vane, bleed, and power lever/N2 relationships. The N1 beat issue was bad enough on the JT9D/767 that we developed what became known as 'super trim' - where the stator vane schedule was adjusted (within the allowable tolerance) to align N1 with EPR.