Originally Posted by 8che
I think you may be confusing over speed with internal failure. The first line of your quote states the same protection for N1/2/3 with EEC adjusting fuel flow. The second part talks about internal failure dealt with by a separate OPU which is a rather different issue. I suspect EEC and OPU are two different things. We are talking only about EEC control on this thread.
Perhaps we have different interpretations of
overspeed protection?
Anyway, the manual does say that the Trent EEC is capable of closing the HP Valve as well as the OPU in response to "overspeed". The Trent EEC has an overspeed system known as
LPTOS. The OPU is only used when the EEC fails to protect the engine with it's normal control and it's LPTOS, and the engine experiences (quote) "severe" overspeed.
Yes, for overspeed protection (mentioned in my manuals) to activate, there has to be a failure of some sort (internal or external to the control system... sensors, EEC, FMU, VSV, shaft, etc).