This happened to me today. At about 10 nm to the airport in the cruise, the ENG light illuminated, NR Fadec comes on in VMS and NR went to 103.8%. At the same time the AMC 1 failure occurs. On checking with the status page it says AMC 1 fail and FADEC 2 fail.
AMC 1 failed ..no problem, just reconfigure and use AMC 2.
FADEC 2 failure..a bit tricky here as the FADEC LIGHT was not on. I raised and lowered the collective slowly and and found that the NR remained at 103.8% so it is not a FADEC failure and no securing of the engines.
After landing when No 2 eng was retarded to IDLE the GOV light comes Flashing on.
Anyone has experienced this not in the book malfunction before?
This is an AMC failure, not a FADEC failure.
Important point: The pilot should never act on anything they see on the STATUS page, it is really only for advice to the technicians.
FADEC failure is only indicated by the FADEC caption on the VMS engine page and the red repeater light near the engine switch
When the AMC fails the Nr datum stops being received by the FADEC so it reverts to its own datum. Since the FADEC does not have access to the airspeed data, it cannot reduce Nr down to 100% at higher speeds, hence the 103.8% in the cruise. The only device that has ARINC data connection with the FADEC is the AMC, so with AMC failure the FADEC has to work in isolation, including using its own pressure and temperature sensors which are less accurate than the airframe sensors. Probably because of this the flashing Gov is triggered and stored, to be displayed on shutdown even if the triggering problem has been dealt with.
We find that, compared to the other boxes on the aircraft, the AMC is fairly unreliable. Whilst it may recover in your case following a reboot, it is likely to fail again soon and so the best course of action is to replace it.
HC