From pass bureau website:

Checking Availability
September 1st-October 16th - All listings must be completed through the Mesa Pass Bureau by completing the American Airlines Travel Request Form, located on the Pass Bureau website. This must be completed 3 business days in advance. US Airways flights still operating under the US Airways banner will still list through Wings and apply to the old program until October 16th.

October 16th- Once US Airways flights are retired, Wings will be utilized to list for American/American Eagle flights. More information to come on this.

What’s Next?
We are working with American on a new employee travel tool that we expect to launch in 2016. The new tool will allow for a more efficient booking process. We will send out updates as they are available regarding the new process.