If engine 1 fails and N1 drops below 5% while N2 remains above 50% for more than 5 secs, the speed trim logic considers this a loss of N1 signal with the engine still running, and the SPEED TRIM FAIL amber light illuminates. SPD LIM appears on the PFD and onside AFDS pitch modes are not available. This is why this occurs only with a seizure or severe damage and not when there´s a flame out.
Placing the Start switch to cont re power the EEC and restores valid ENG FAIL signal. The SPD LIM flag is removed, the speed tape yellow and red bands are recovered and the speed trim fail amber lt extinguishes.