Failsafe problem when fly arducopter

i have a problem, before fly i check my quadcopter (arducopter v2.8, ESC turnigy 30A, brushless motor sannysky 700kv, remote futaba t8fg) and failsafe for motor 1,2,3,4 work correctly, when i’m trying to fly my drone, it fly for 3 minutes, after that my drone fall and crash, then i check the failsafe and it not work correctly again, why did it happen??

Post dataflash log. …