RSA means the rakes of these two trains will be used in exchange..
For example Hussain Sagar reaches Mumbai at 4:30 AM it will have some maintainence at mumbai and will return as CTSM-HYB express which leaves at 12:45 PM..
Same the HYB-CSTM which reaches at CSTM at 1:00 PM and will have some maintainence at CSTM and will return back as Hussain sagar at 9:50 PM from CSTM..
Same...
more... in case of return direction also..This is being done to reduce the rake idle time at yard...