"Awaiting AE decision" has lasted for nearly four months. What should I do? The status of my manuscript is "Awaiting AE decision", and it has lasted for nearly four months.
I have sent two pieces of mail to AE to inquire of the status, but I have not received any reply.
What does this situation mean? What should I do? 
..While, I am still waiting, no reply.
It could mean they're overworked or disorganized. Four months seems substantial.  Maybe you could try a phone call.