ARFOR;
- If one engine (either one) failed, at what shaft (% RPM) would the associated GEN trip out?
A quick review of the AOM does not provide an RPM. However, if I understand your point, you may be thinking that a windmilling engine may supply electrical power and that would not be the case as a windmilling high-pressure compressor section rotation at cruise speed is below the RPM required for electrical generation (The RR Trent would be around 12 to 15% if I recall correctly from the sim but someone with current experience may be able to confirm/correct this. I believe the gearcase is taken off the N3 but, frustratingly, the AOM doesn't tell us - the AOM NTK - need-to-know, description is about the level of, "the engine has 3 rotating sections with turbines attached...).
- Notwithstanding the above, following a single engine (either one) failure, would AC1 remain energized by the other power plant? If yes;
- Following the inevitable ECAM/s, would ACARS output message/s?
Under normal (design) circumstances, all AC and DC busses remain powered; there is some load shedding, (galleys) in loss of generation.
As you say, the ECAM would display the failures and the required actions. FLR/WRN category messages would be generated and recorded by the FIDS, (Fault Isolation and Detection System), collated by the CMS (Central Maintenance System) and sent to the ACARS for maintenance action. In short, they would be a part of any transmitted messages.
- Following an asymmetric failure (whilst in ALTN 2), how promptly would the PF need to get rudder in to avoid yaw induced roll?
It is entirely dependant upon yaw developed in the spectrum from idle thrust to takeoff/go-around power. An engine failure at idle thrust would not require any rudder at all; an engine at takeoff thrust requires an immediate response, and initially requires about 14deg of rudder, from which one backs off (after trimming out the yaw), depending upon the airplane's needs. In cruise, an engine failure would require an immediate but small application of rudder, (gently!). As with all high-altitude flight one must be careful with the use of controls because thin air provides so little damping effect. Providing rudder is used judiciously, roll-due-to-yaw is not a problem.