Allied Telesis AT-9448Ts/XP (Basic Layer 3) - Manual (Page 97)

AT-9400Ts Stack Installation Guide
97
System Fault LED is Blinking
If the system FAULT LED is blinking, no action is required. A blinking
FAULT LED indicates that the switch is downloading a new version of the
management software or is updating the active boot configuration file. The
LED stops blinking after the switch has downloaded the new management
software or updated the boot configuration file.