I've been following this thread fairly closely, and I really don't think my points have been answered 100%. And I *did* re-read from post #1738.
If I understand the "degraded" mode correctly the engine controller falls back to a fail-safe mode because some sensor data is not available. I can understand how #1 engine degraded, because the wiring in the left wing was damaged. But #4 engine is on the other wing - so what went wrong to cause that to "degrade" ? If that's explained somewhere please let me know, 'cos I can't see it
.
Apologies if I'm just illiterate/stupid !