He chuckled
In answer to the question (and apologies to Charlie if I misquote):
Three scenarios could be possible.
1. The problem could be due to a mechanical linkage jam within the HMU/FMU. This is a known problem that can occur with rapid movement of the FFCL, with a certain mod state HMU, most of which should have beeen replaced. However this could only happen in manual mode. The jam could be overcome, but it would be a sudden release followed by a floppy FFCL.
2. More likely, and possible in mixed mode, would be the FFCL cable having some sort of crimp or bunching. It is a long cable and it is not normally exercised, so a latent problem may go un-noticed for some time. It would give the symptons described and would be a more progressive release.
3. A further possibility is a problem in the FFCL quadrant itself. There are two microswitches at the top end of the gate to allow entry from the outer track to the inner track. If the inner track switch was damaged it could leave the FFCL midway between the tracks, and again this would only manifest itself on the occasion the FFCL was attempted to be retarded with the pilot thinking it was in the inner track. Again, normally the problem would not manifest itself as the FADEC would behave normally in FLY mode at all other times.
Hope this helps; it certainly led to an interesting discussion with Charlie.